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That stars can eat planets is axiomatic. If a small enough planet gets too close to a large enough star, the planet loses. Its fate is sealed.

New research examines how many stars eat planets. Their conclusion? One in twelve stars has consumed at least one planet.

The evidence comes from co-natal stars, which aren’t necessarily binary stars. Since these stars form from the same molecular cloud, they should have the same ingredients. Their metallicity should be nearly identical.

But for about one in twelve stars, there are clear differences.

The new research is titled “At least one in a dozen stars shows evidence of planetary ingestion,” and it’s published in the journal Nature. The lead author is Fan Liu, an ASTRO 3D Research Fellow in the School of Physics and Astronomy at Monash University, Melbourne, Australia.

“Astronomers used to believe that these kinds of events were not possible.”

Yuan-Sen Ting, co-author, ASTRO 3D researcher from the Australian National University

“Stellar chemical compositions can be altered by ingestion of planetary material and/or planet formation, which removes refractory material from the protostellar disk,” Liu and his colleagues write in their paper. “These ‘planet signatures’ appear as correlations between elemental abundance differences and the dust condensation temperature.”

The authors explain that these signatures are elusive. The key to finding them is to locate co-natal stars, stars that were born together and are still moving together through space.

“We looked at twin stars travelling together. They are born of the same molecular clouds and so should be identical,” said lead author Liu.

The researchers started by using the extreme accuracy of the ESA’s Gaia spacecraft. Gaia’s data allowed the researchers to identify 125 co-moving pairs of stars. Of those, 34 were considered too widely separated but were still used as a control group. The researchers then examined the remaining 91 pairs spectroscopically to determine their chemistry. They used powerful telescopes to gather this data: the Magellan Telescope, the Very Large Telescope, and the Keck Telescope. The large amount of accurate data generated by these ‘scopes allowed the researchers to detect chemical differences and made the findings possible.

“Thanks to this very high precision analysis, we can see chemical differences between the twins,” said Liu. “This provides very strong evidence that one of the stars has swallowed planets or planetary material and changed its composition.”

Liu points out that their findings don’t include stars like red giants that expand when they leave the main sequence and consume nearby planets. “This is different from previous studies where late-stage stars can engulf nearby planets when the star becomes a very giant ball,” Dr. Liu said.

This figure from the study illustrates some of the team’s findings. The top panel shows the different chemical abundances of some chemicals between one pair of co-natal stars. The bottom panel shows the same in percentage differences. Image Credit: Liu et al. 2024.

These results required some detailed analysis. When determining the metallicity of the co-natal stars and how planetary material could explain the different metallicities, the researchers had to account for atomic diffusion. Atomic diffusion can transport different chemicals around in stars, which can change how abundant different chemicals can appear to be. Stars from the same cluster, and co-natal stars, can show different abundances even though they’re the same overall.

However, atomic diffusion leaves a different chemical fingerprint, and the researchers were able to determine how atomic diffusion affects apparent abundance versus how the engulfment of planetary material affects it.

There’s a lot of specific scientific information in this figure from the study. But the primary takeaway is that the abundance of each chemical element in this pair of co-natal stars more closely matches a planet engulfment model (blue dashed line) than atomic diffusion (pink dashed line.) Image Credit: Liu et al. 2024

The results show that some co-natal stars have different metallicity, so some of them have absorbed planetary material. But the researchers point out that some of the results may not come from planetary engulfment. It’s possible that in some of these pairs, one star absorbed material from its protoplanetary disk, which would also change its metallicity.

“It’s complicated. The ingestion of the whole planet is our favoured scenario, but of course, we can also not rule out that these stars have ingested a lot of material from a protoplanetary disk,” he says.

Showing that stars can absorb planets puts another wrinkle into our understanding of stars and their planetary systems. Engulfment doesn’t happen a lot, according to these results, but the fact that it does is intriguing. It leads to questions. How and why does it happen? What situations lead to this engulfment? How does it affect the exoplanet population, and could it affect potential habitability somehow? Engulfment leaves its mark on the star; how does it affect the planetary system?

“Astronomers used to believe that these kinds of events were not possible, said study co-author Yuan-Sen Ting, ASTRO 3D researcher from the Australian National University. “But from the observations in our study, we can see that, while the occurrence is not high, it is actually possible. This opens a new window for planet evolution theorists to study.”

The post One in Twelve Stars Ate a Planet appeared first on Universe Today.

Communication between spacecraft relies upon line of site technology, if anything is in the way, communication isn’t possible. Exploration of the far side of the Moon is a great example where future explorers would be unable to communicate directly with Earth.  The only way around this is to use relay satellites and the Chinese Space Agency is on the case. The first Queqiao-1 was able to co-ordinate communications with Chang’e-4 landers and now they are sending Queqiao-2 to support the Change’e-6 mission. 

If you have ever gazed upon the Moon you might have noticed that it always has the same hemisphere facing the Earth. This phenomenon is known as captured or synchronous rotation. It may look like the Moon isn’t rotating but in reality the time it takes to spin once on its axis is the same as the time it takes to complete one orbit around the Earth, keeping one hemisphere constantly facing us. Explorers on the near side of the Moon have no trouble communicating with transmissions taking just over one second to reach home. Explore the far side of the Moon and you have a problem. 

The Chang’e 5 test vehicle captured this beautiful view of Earth over the far side of the Moon on October 28, 2014. Credit: Chinese national space agency (CNSA) and Chinese Academy of Sciences (CAS)

To overcome the problem China have launched a 1.2 ton communication satellite known as Queqiao-2. It’s name originates from the mythological bridge made from magpies. In the Chinese tale, the magpies formed a bridge across the Milky Way to allow the lovers Vega and Altair to be together for one night once a year. Two miniature satellites were also launched Tiandu-1 and Tiandu-2 from the island of Hainan.

On arrival it will orbit the Moon and provide a relay for the Chang’e-6 lander which is slated to launch in May.  It will join satellites from United States, India and Japan to support the exploration of the far side of the Moon. Chang’e-6 will collected samples from an ancient basin. Not only will it serve the communications for Change-6, it will transfer communications for Chang’e-7 and ‘8. Both craft are to be launched in the years ahead 2026 and 2028 respectively. 

The orbit of Queqiao-2 will take it almost over the south pole in an elliptical orbit. It will reach an altitude of 8,600 km so that communication can be achieved for a little over eight hours. At its closest, it will sweep over the lunar surface at an altitude of 300 km.

The ultimate goal of the Chinese Space Agency is to create a network of satellites, not too dissimilar (but not quite on the same scale) to the growing Space X constellation which is building a global internet presence. The purpose of Tiandu-1 and Tiandu-2 is to test the concept of such a constellation. 

China’s longer term aspirations include a research station at the lunar south pole and for this to be viable, communication relays are essential to establish communication, navigation and remote sensing. 

Source : China launches signal relay satellite for mission to moon’s hidden side

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Totality and the April 8th total solar eclipse offers a rare chance to study the Sun.

We’re less than three weeks out now, until the April 8th total solar eclipse crosses North America. And while over 31 million residents live in the path of totality, many more will make the journey to briefly stand in the shadow of the Moon. Several scientific projects are also underway to take advantage of the event.

The eclipse traverses Mexico, the United States from Texas to Maine, and the Canadian Maritime provinces before heading out over the Atlantic. Maximum totality for this eclipse in 4 minutes and 27 seconds, longer than the 2017 total solar eclipse. This is the only total solar eclipse worldwide for 2024, and the final total solar eclipse for a generation for the contiguous United States until 2044.

A Brief History of Total Solar Eclipse Science

Eclipses have always offered astronomers a chance to carry out rare observations. The element helium (named after ‘Helios’ the Greek god of the Sun) was discovered in the solar chromosphere during the August 18th, 1868 total solar eclipse. Astronomers swept the sky near the eclipsed Sun in July 29th, 1878, looking for the hypothetical planet Vulcan. World War I thwarted astronomer’s plans to test Einstein’s Theory of General Relativity during the August 21st, 1914 eclipse. This had to wait until Arthur Eddington led an expedition to Principe in 1919. Eddington vindicated Einstein with measurements of the deflection of stars observed near the Sun during totality.

Stranger experiments continued right up into the 20th century. One of the more bizarre eclipse experiments was hunting for the elusive ‘Allais Effect,’ looking for the deflection of a pendulum during totality. Alas, Maurice Allais’ findings alluding to this fringe idea have never been replicated. Maybe LIGO Livingston just outside the path of totality on 2024 could take up the challenge?

Four Eclipse Science Projects

In 2023, NASA selected four major experiments to chase totality:

1. The Solar Patrol sunspot campaign: This effort is led by Thangasamy Velusamy out of NASA’s Jet Propulsion Laboratory. This initiative seeks to monitor subtle changes in the magnetic fields of active sunspot regions as the Moon passes over them. The team will use the 34-meter Goldstone Apple Valley Radio Telescope based in California (outside of the path of totality) to carry out this experiment. We’re headed towards the peak of Solar Cycle 25 over the coming year, so the odds are pretty good that the Sun will be dappled with multiple sunspots, come eclipse day.

2. SuperDARN to probe the ionosphere: Led by Bharat Kunduri out of Virginia Polytechnic Institute and State University, this experiment seeks to measure how the upper ionosphere reacts to the eclipse. Crucially, totality passes over three SuperDARN (Super Dual Auroral Radar Network) sites during the eclipse, offering an unprecedented opportunity.

3. Pro/AM ‘Listening Party’ to observe QSOs: Ham radio operators are familiar with the enhanced nighttime reflectivity of the upper ionosphere. This effect allows for reception of distant stations that are otherwise silent in the daytime. This sort of contact is known as a ‘QSO’ in ham radio-speak, and it also occurs during an eclipse, as totality briefly mimics the approach of night. Nathaniel Frissell of the University of Scranton is leading an effort to make QSO contacts on April 8th. A good strategy is to pick an AM station a few hundred miles distant and listen before, during and after totality passes. Even today, most cars still come equipped with AM/FM radios. This is also an experiment that can be done from outside of the path of totality.

A modified, eclipse-chasing WB-57 aircraft is towed out for a mission. NASA Chasing the Shadow

4. NASA’s WB-57 missions to take flight once again. The most ambitious endeavor is once again underway, as NASA’s two converted WB-57 Canberra aircraft will once again chase the shadow of the Moon. NASA owns the last three Canberra aircraft still in service. Two of these aircraft will fly out of Ellington Field outside of Houston, Texas on eclipse day. The jet aircraft will intercept the Moon’s shadow, which will be moving at over 2,500 miles per hour. This allows for an extra two minutes of totality. Both aircraft will carry a suite of cameras and spectrometers, allowing astronomers to analyze the inner corona very near the Sun. Studying the region could go a long ways towards solving the ‘coronal heating problem,’ a mystery evolving why the corona is exponentially hotter than the photosphere of the Sun.

Images of the Sun from GOES-16, versus the Sun during eclipse (far right) showing loops in the lower corona. NASA

Observations from the 2017 eclipse hinted that oscillations in the lower corona may feed ‘nano-flares’ that pump energy into the outer corona. This time, two new observatories will be on hand to back up NASA’s eclipse measurements. These are the European Space Agency’s Solar Observatory (SolO) and NASA’s Parker Solar Observatory.

The flight will also continue the campaign to scan the sky near the eclipsed Sun to hunt for elusive Vulcanoid asteroids interior to the orbit of Mercury. General Relativity did away with the need to evoke an inter-Mercurial world to explain the anomalous precession of Mercury’s orbit. The jury is still out, however, on whether smaller asteroids could still exist near the Sun. MESSENGER scoured the region near the Sun en route to Mercury. NASA will once again look for Vulcanoids as a secondary objective during the 2024 eclipse.

NASA has also chased eclipses aloft using Gulfstream III aircraft:

More Total Solar Eclipse Science

Other citizen-science projects are also planned for April 8th. One intriguing project is the Citizen Continental-America Telescope Eclipse network, known as Citizen CATE. This project sees volunteers setup along the total solar eclipse path, with the objective of augmenting corona observations.

An animation of the corona in polarized light, as seen during the 2017 total solar eclipse. NASA/Gopalswamy et al.

I have a deep respect for all those who are devoting precious time during totality to eclipse science. Perhaps, you’ll simply be happy will clear skies to enjoy the view. If you haven’t got your eclipse glasses yet to safely obverse the Sun, Astronomy For Equity still has ‘em available. Hey, they’re for a good cause…

Good luck and clear skies to all who are headed into the shadow of the Moon on eclipse day, whether its for the cause of science, or just to enjoy the view.

The post NASA Experiments Planned for the April 8th Total Solar Eclipse appeared first on Universe Today.

After over 70 successful flights, a broken rotor ended the remarkable and groundbreaking Ingenuity helicopter mission on Mars. Now, NASA is considering how a larger, more capable helicopter could be an airborne geologist on the Red Planet. For the past several years scientists and engineers have been working on the concept, proposing a six-rotor hexacopter that would be about the size of the Perseverance rover.

Called the Mars Science Helicopter (MSH), it would not only serve as an aerial scout for a future rover, but more importantly, it could also carry up to 5 kg (11 lbs) of science instruments aloft in the thin Martian atmosphere and land in terrain that a rover can’t reach.

A new paper presented at the March 2024 Lunar and Planetary Science Conference outlines the geology work that such a helicopter could accomplish.

The paper, “Unraveling the Origin and Petrology of the Martian Crust with a Helicopter,” notes there are several outstanding questions about the makeup and history of Mars’ surface, especially with recent discoveries of unexpected dichotomies in the composition of basaltic rocks. In observations from the Mars rovers and orbital spacecraft, some regions appear to have been influenced by water while some have not.

“Up to last decade, we thought that magmatic rocks were only basaltic on Mars,” said Valerie Payré from the University of Iowa, the paper’s lead author. “But with recent rover and orbital measurements, we observed that there is a wide diversity of magmatic rocks similar to what we see on Earth.”

Payré explained via email that there are rocks on Mars with elevated silica concentrations called felsic rocks – feldspar and silicate — that are rich in elements and were not expected to be found on the Martian surface.

“We measured these with the Curiosity rover and have some hints of where there might be others using orbital measurements,” Payré said. “However, close-up images (millimetric scale) and composition analyses are lacking from the orbital dataset to know if these felsic rocks are widespread on Mars or just at a few locations. This is yet highly important to understand what the crust of Mars is made of and if it is similar to Earth’s crust, which has implications regarding the formation of the planet and even past climate.”

First X-ray view of Martian soil – feldspar, pyroxenes, olivine revealed (Curiosity rover at “Rocknest”, October 17, 2012). Credit: NASA/JPL-Caltech/Ames

Payré and her team feel that a helicopter would be perfect to explore places where a rover could never traverse, such as terrains that are too high in altitude, since landing there would require too much fuel.

The instruments they propose include a miniaturized visible and near-infrared (VNIR) spectrometer for small scale mineralogical mapping and a small Laser Induced Breakdown Spectrometer (LIBS) with a micro-imager, an instrument similar to the ChemCam laser instrument on both the Curiosity and Perseverance rovers. In their paper, the team writes that a helicopter with these instruments could travel kilometers to detect promising felsic terrains, and measure their composition at a micron scale.

“We could fly over these possible felsic terrains and look at their minerals using a visible/near infrared spectrometer, land on locations of interest, take close-up images, and measure the compositions of these rocks with the LIBS,” Payré said. “We could finally know what Mars’ crust is, and better constrain how it formed.”

A graphic show the parts of the Ingenuity helicopter. Credit: NASA

There could also be an onboard a magnetometer, which measures magnetic field anomalies, to better understand how Mars’ magnetic field operated, which is still uncertain. Mars does not presently have a global magnetic field, but had one early in its lifetime.

“Such payload would finally enable us to better understand the past climate on Mars by measuring the composition and minerals of sedimentary rocks of various age,” Payré told Universe Today.

A conceptual design paper published in 2020 proposed a Mars hexacopter with a mass of about 31 kg (70 lbs) and a total diameter of just over four meters (13 feet). Each set of rotors would have blades about 0.64 meters (2 ft) long.  The helicopter would be powered by a rechargeable solar cell. This would not only power the rotors, but the desired scientific instruments. 

A model of NASA’s Mars Science Helicopter concept. Credit: NASA.

This helicopter could move as fast as 30 meters a second (60 mph) but also could hover over a spot for as long as five minutes. Engineers from Ames Research Center, the Jet Propulsion Lab and the University of Maryland wrote that MSH could fly with a range of up to 10 km (6.2 miles) per flight. With this speed and range, MSH could potentially cover as much ground in a few days as rovers like Perseverance and Curiosity have traversed in years.

“The fact that a helicopter can fly would facilitate the mission to visit to places that would be inaccessible for a rover, and we could access locations that we never imagined before,” Payré said.

Payré and team proposed several landing sites including Gale Crater Gale crater where evolved felsic rocks were found by the Curiosity Rover; the massive canyon of Valles Marineris, where orbital observations have revealed a deep crust with feldspar-bearing rocks; and Hellas basin, 2,300 km impact crater known to have layers of feldspar. 

Annotated view of Valles Marineris from the High-Resolution Stereoscopic Camera (HRSC) on the Mars Express spacecraft. Credit: ESA/DLR/FU Berlin (G. Michael)

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The US Government budget announcement in March left NASA with two billion dollars less than it asked for. The weeks that followed have left NASA with some difficult decisions forcing cuts across the agency. There will be a number of cuts across the agency but one recent decision came as quite a shock to the scientific community. NASA have just announced they are no longer going to support the Chandra X-Ray Observatory which has been operational since 1999 and made countless discoveries. 

Chandra was launched back in 1999 and has become pivotal in the world of X-ray astronomy. X-ray observatories like Chandra have to be placed in orbit because the atmosphere blocks the X-ray radiation from reaching Earth. Like other high energy telescopes, the mirrors of Chandra have to be placed at shallow angles to the incoming high energy beams. If they were placed perpendicular the X-rays would zip straight through. Instead, multiple mirrors are placed at shallow angles to gently guide the radiation to a focus. 

Since its launch it has captured high resolution X-ray images of black holes, supernova remnants, pulsars and galaxy clusters. The X-rays allow us to look deep inside these extreme objects to show detail which is usually impossible to see. It’s first image was the supernova remnant Cassiopeia A, it revealed forward and reverse shockwaves and ejecta from the pre-supernova state.

This X-ray image of the Cassiopeia A (Cas A) supernova remnant is the official first light image of the Chandra X-ray Observatory. The 5,000 second image was made with the Advanced CCD Imaging Spectrometer (ACIS). Two shock waves are visible: a fast outer shock and a slower inner shock. The inner shock wave is believed to be due to the collision of the ejecta from the supernova explosion with a circumstellar shell of material, heating it to a temperature of ten million degrees Celsius. The outer shock wave is analogous to an awesome sonic boom resulting from this collision. The bright object near the center may be the long sought neutron star or black hole that remained after the explosion that produced Cas A.

NASAs budget statement was released on 11 March where it revealed its plans for 2025 and beyond. In the statement it read “The reduction to Chandra will start orderly mission drawdown to minimal operations.” Thankfully NASA has already identified a plan of action should Chandra experience mission-ending failure. The loss of funding and the decision to scale back Chandra activity has meant these procedures swing into action. They include the closedown of flight operations, finalisation of data and source catalog, documentation of calibration and other critical products and much more. 

The budget document went on with the rationale for the decision “The Chandra spacecraft has been degrading over its mission lifetime to the extent that several systems require active management to keep temperatures within acceptable ranges for spacecraft operations. This makes scheduling and the post processing of data more complex, increasing mission management costs beyond what NASA can currently afford.”

The statement refers to spacecraft degradation which does of course come to all spacecraft in time if not repaired and upgraded. One of the key issues it temperature control. To be effective Chandra needs to be kept at a specific temperature but since 2005 the temperature has been increasing. To overcome the problem, thermal models have been developed along with processes to counteract the rising temperature with no degradation in quality. However to continue operations the models need to be updated which takes time and money.

In April, NASA plans to go through a review process to see if operations may be able to continue in the future given the budget restrictions. For now though, it seems Chandra operations are set to be put on hold for the foreseeable future. 

Source : A Letter to the Chandra Community

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The Moon is practically begging to be explored, and the momentum to do so is building. The Artemis Program’s effort to return astronauts to the Moon for the first time since the Apollo missions captures a lot of attention. But there are other efforts underway.

In 2023, the ESA put out a call for small lunar missions. The call was associated with their Terra Novae exploration program, which will advance the ESA’s exploration of the Solar System with robotic scouts and precursor missions. “Humankind will benefit from the new discoveries, ambitions, science, inspiration, and challenges,” the ESA explains on their Terra Novae website.

Terra Novae has several goals, one of which is to “Land multiple scientific payloads on the surface of the Moon, prospecting for the presence of water and other volatile materials that will both reveal its history and help prepare sustainable exploration by locally sourced space resources.”

In response to the ESA’s call, a team of European researchers have proposed the LunarLeaper. The LunarLeaper is a hopping robot that would visit a lunar skylight, a collapsed part of a lunar lava tube. The robot would give us our first look at the lunar subsurface and the lava tubes.

This illustration shows the LunarLeaper in different locations around the rim of a skylight, a collapsed segment of a lunar lava tube. From its position on the rim, the robot would map the skylight and the tube floor and walls and take various scientific measurements, including detecting volatiles. Image Credit: LunarLeaper

There are good reasons to explore these lava tubes. The lunar surface is exposed to solar and cosmic radiation without the benefit of a protective atmosphere or magnetosphere like Earth. Astronauts could shelter in these tubes inside habitat modules. Several meters of rock overhead would provide protection from radiation and from the Moon’s temperature swings. There could be laboratory modules and other modules as well. The tubes, if suitable, could shelter an entire base.

The other reason is scientific. These tubes are a window into the Moon’s volcanic past. They’re a record of the magnitude and timing of volcanic activity.

The LunarLeaper is a ~10 kg (22 lbs) leaping robot with three legs. It’s based on the ETH SpaceHopper design which has been refined over four years of development. SpaceHopper is designed to visit asteroids with much weaker gravity than the Moon, but the design can be adapted to work on the lunar surface.

The LunarLeaper team proposes a mission to the Marius Hills region. It’s a region in Oceanus Procellarum, a vast lunar mare on the near side of the Moon. It’s a volcanic region covered in basalt floods from ancient volcanic activity. Marius Hills is named after the 41 km (25 mi) diameter crater Marius and is littered with volcanic features like rilles, domes, and cones.

The particular feature of interest in Marius Hills is the Marius Hills Pit (MHP), a collapsed skylight granting access into what might be an extensive lunar lava tube system. The Lunar Reconnaissance Orbiter captured an image of the intriguing opening featured in the lead image. That’s where the LunarLeaper would do its work.

The Marius Hills region is full of volcanic features and the MHP, an opening into underground lava tubes. Image Credit: NASA/USGS

The Leaper would move around the rim of the MHP, capturing images of the pit walls and the floor. It would also use its suite of scientific instruments to gather pertinent data. Its instrument suite would include a gravimeter, a ground-penetrating radar, a dedicated science camera, and hopefully a spectrometer.

The LunarLeaper team outlines four questions the mission hopes to answer:

1. Is there a lava tube under Marius Hills? It certainly appears like there could be, but there’s no confirmation yet, and only a mission to the region can answer the question for certain.
2. Could astronauts use the tube for habitation? If it’s stable enough they could, and that’s something the LunarLeaper can figure out.
3. How were the tube and pit formed? What volcanic processes were at work? There are lava tubes on Earth. Did they form the same way on the Moon? LunarLeaper can examine the layers on the walls of the tube for clues.
4. What’s contained in the regolith outside the tube? Are there ancient pieces of paleoregolith underground near the pit? Surface lunar rocks are degraded and eroded, but buried regolith could hold clues to the early Solar System, including the Sun.

Though there are hundreds of similar pits on the Moon, MHP appears to be the most promising one. It’s been imaged from different illumination angles, and the imaging supports the idea that a tube extends underground beyond the skylight. Since the Marius Hills is filled with volcanic features, an extended tube isn’t unlikely.

The LunarLeaper would travel around the surface near the MHP and use its ground-penetrating radar to uncover the extent of the tube system. Other proposed missions are aimed at lava tubes and skylights, but they tend to be more complex, larger, and more expensive. As a 10 kg hopping robot, LunarLeaper would be a wise choice for the first mission to characterize the MHP prior to sending a more complex, thorough mission.

When it comes to exploring the pit, the LunarLeaper has a significant advantage over a wheeled rover. Wheeled rovers select routes based on obstacle avoidance. They have some strict limitations when it comes to the terrain they can safely and effectively traverse.

However, the rim of the MHP is expected to be challenging. There is likely complex terrain and steep slopes right near the opening. Getting as close as possible to the rim will give better imaging and science results. The LunarLeaper has an advantage over wheeled rovers in this type of terrain, though the tradeoff is its much lighter payload.

However, as a first step in exploring the MHP, the LunarLeaper has some clear advantages.

This image from LunarLeaper shows some of the details of the area near the MHp and how the Leaper would go about exploring it. A shows the topography around the MHP and the nearby rille. B is a zoom-in of the white box in A. It shows a potential landing zone and the route the Leaper could follow to the MHP. It shows a large boulder en route as an example of an interesting object to examine on the way. C shows the MHP itself, with some of the challenging terrain visible, and also shows the slope in colour-coded degrees. Image Credit: LunarLeaper

The LunarLeaper team says that the small robot could be delivered to the lunar surface by one of the several small landers being designed by different companies. They peg the cost at about 50 million euros. They also say that this type of legged jumping robot could be a big part of future space exploration and that their mission, if chosen, could be a key development for the future.

The post It’s Time to Study Lunar Lava Tubes. Here’s a Mission That Could Help appeared first on Universe Today.

Nature often defies our simple explanations. Take comets and asteroids, for example. Comets are icy and have tails; asteroids are rocky and don’t have tails. But it might not be quite so simple, according to new research.

That nice, clean definition took a hit in 1996 when a pair of astronomers discovered that what was thought to be a main-belt comet was actually an asteroid. The object is named 7968 Elst–Pizarro after the two scientists. It displayed a comet-like dust tail at perihelion.

These images from the La Silla Observatory show the active asteroid 7968 Elst–Pizarro. Its tail is clearly visible. Image Credit: By ESO – https://www.eso.org/public/images/eso9637a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=26500568

7968 Elst-Pizarro was classified as a main-belt comet (MBC) because it orbits within the main asteroid belt between Mars and Jupiter. It’s still called an MBC sometimes. However, its icy component that sublimates into a vapour trail likely comes from a small surface crater with volatiles in it rather than from a homogenous ice component. That’s why it’s called an active asteroid.

Active asteroids are unusual and rare objects. To understand them and their place in the Solar System’s history, scientists want to find more of them. That led to the creation of NASA’s Active Asteroids Project.

Now, the Active Asteroids Project has announced the discovery of 15 new active asteroids. These findings are in a new paper published in The Astronomical Journal. It’s titled “The Active Asteroids Citizen Science Program: Overview and First Results,” and the lead author is Colin Chandler from the Dept. of Astronomy & the DiRAC Institute at the University of Washington in Seattle. Among the co-authors are nine volunteer citizen scientists.

“For an amateur astronomer like me, it’s a dream come true,” said volunteer Virgilio Gonano from Udine, Italy. “Congratulations to all the staff and the friends that also check the images!”

“Active objects are rare in large part because they are difficult to identify, so we ask volunteers to assist us in searching for active bodies in our collection of millions of images of known minor planets,” the authors of the paper write. Active asteroids aren’t the only objects they’re trying to find. There are several other types.

Centaurs are small Solar System bodies that orbit between Neptune and Jupiter. Centaurs have crossed the orbits of one or more giant planets, making their orbits unstable. They have traits in common with both comets and asteroids, and about 30 of them have dust-like comas. These are the active ones.

The Active Asteroid Project is also trying to identify active quasi-Hilda asteroids (QHAs). QHAs are beyond the asteroid belt but within Jupiter’s orbit. Astronomers have discovered about 3000 of them, and about 15 of them have tails of gas and dust.

Active asteroids have asteroid-like orbits but have tails or comae like comets do. Image Credit: Mark Garlick/SPL

The Project also hopes to identify Jupiter family comets (JFCs.) JFCs are comets with very short orbital periods of less than 20 years. They’re contained within Jupiter’s orbit but may be captured Kuiper Belt Objects. They likely originated from collisions between objects in the Kuiper Belt and then were captured by Jupiter.

All of these objects have something to tell us about how the Solar System formed. Beyond that, they can help unravel the mystery of Earth’s water. There’s another, more forward-thinking reason for wanting to find these active objects. Their water can be split into hydrogen for rocket fuel and oxygen for respiration in future missions, though that’s so far in the future it’s esoteric.

This image shows one of the active asteroids found by citizen scientists involved with the Active Asteroid project. It’s named 2015 VA108, and the green arrow highlights the asteroid and its tail. Image Credit: Colin Orion Chandler (University of Washington)

The commitment of the citizens taking part is admirable. Since the effort launched on August 31st, 2021, about 8300 volunteers have taken part. Collectively, they’ve examined about 430,000 images.

“I have been a member of the Active Asteroids team since its first batch of data,” said volunteer Tiffany Shaw-Diaz from Dayton, Ohio. “And to say that this project has become a significant part of my life is an understatement. I look forward to classifying subjects each day, as long as time or health permits, and I am beyond honoured to work with such esteemed scientists on a regular basis.”

The images in the project all come from the Dark Energy Camera (DECam.) DECam is a high-performance camera with a wide field of view that’s mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory.

The images are filtered by query across multiple databases and image archives before they’re placed in front of the eyes of the citizen scientists. This includes the Minor Planet Center (MPC), the JPL Small-Body Database, the Canadian Astronomy Data Centre, and the National Optical and Infrared Laboratory (NOIRLab) AstroArchive. They also consider the observing telescope’s field-of-view, the objects’ coordinates and semi-major access, and multiple other factors.

The Project then uses scripts to download the desired data from astronomical archives. Then, they generate uniform DECam thumbnail images of each object. This results in millions of images of potential active asteroids or similar objects. There’s no possible way there are enough professional astronomers to handle this much work. So, the images are grouped up into “subject sets” and sent to the citizen scientists who put the effort in and make the project feasible.

Before the volunteers work with any real images, they’re trained on a set of images of objects that display some activity, like a tail or a coma. Then, the participants give them a score from zero (unidentifiable/missing;) to 9 (definitely active, overwhelming activity indicators.) “All training images in Active Asteroids are derived from those images to which we applied a score of ?5; our minimum threshold, for which we consider the activity to be highly likely,” the authors explain.

In each image, a green reticle identifies the object of interest. The citizen scientists are asked a fairly straightforward question: do they see activity (i.e., a tail or coma) coming from the central object?

This is one of the DECam thumbnail images in the project. It shows the active asteroid (62412) 2000 SY178. In the project’s analysis system, this object received a score of 0.35, below the threshold of 0.473 needed to classify it as an active object. Image Credit: Chandler et al. 2024/Active Asteroid Project.

Over time, most citizen scientists became more productive. But not always.

This figure from the study shows the number of images classified through time by 10 randomly selected participants, numbered from 0 to 9. Most got better over time, though number 7 seemed to buck that trend. Image Credit: Chandler et al. 2024/Active Asteroid Project.

Each subject set requires a certain amount of preparation by the professional astronomers. That has to be balanced by the work and time it takes a citizen scientist to go through it. After some experimenting, the project settled on sets of about 22,000 images, which took a citizen participant about four to eight weeks to go through.

The project takes place on the Zooniverse platform, home to many other citizen science projects. One of the benefits of that platform is that the citizen participants and the professional astronomers can talk with one another on the “Talk” discussion boards on Zooniverse. “Surprisingly, we have made discoveries that first come to light on the Talk pages, well before the subject set was fully retired,” the authors of the paper write.

This is just the first data release from the project. Finding 15 active asteroids and one Centaur is just the beginning. In fact, the project has produced more than 20 discoveries, resulting in multiple publications. And they’re not done.

They intend to continue working and improving their methods. The Project is also looking ahead to the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), which will produce an enormous number of images for evaluation.

If you’re interested in participating, visit the project website.

“The Active Asteroids project is ongoing and can be accessed through the project website,” the authors write. “Participation is easy and intuitive and can take as little as a few minutes to contribute.”

The post Citizen Scientists Find Fifteen “Active Asteroids” appeared first on Universe Today.

The Earth’s place in space is a fairly familiar one with it orbiting an average star. The star – our Sun – orbits the centre of our Galaxy the Milky Way. From here onwards, the story is less well known. The Milky Way is part of a large structure called the Laniakea Supercluster which is 250 million light years across! That really is a whacking great area of space and it contains at least 100,000 galaxies. There are larger superclusters though like the newly discovered Einasto Supercluster which measures an incredible 360 million light years across and is home to 26 quadrillion stars!

When I give public lectures, I always get a strange satisfaction out of telling the audience that galaxies don’t exist! I go on to explain that, like a city which is a collection of stuff, galaxies are collections of things bound together under the force of gravity. A typical galaxy is simply a collection of stars, nebulae, clusters, planets, comets and so on, take them away and a galaxy won’t exist! Superclusters are largely the same, just a collection of galaxies bound together (well, not completely) under the force of gravity. 

Hot stars burn brightly in this image from NASA’s Galaxy Evolution Explorer, showing the ultraviolet side of a familiar face. At approximately 2.5 million light-years away, the Andromeda galaxy, or M31, is our Milky Way’s largest galactic neighbor. The entire galaxy spans 260,000 light-years across — a distance so large, it took 11 different image segments stitched together to produce this view of the galaxy next door. The bands of blue-white making up the galaxy’s striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. Eventually, these dusty lanes will be blown away by strong stellar winds, as the forming stars ignite nuclear fusion in their cores. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago. When observed in visible light, Andromeda’s rings look more like spiral arms. The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA’s Spitzer Space Telescope. Astronomers using Spitzer interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago. Andromeda is so bright and close to us that it is one of only ten galaxies that can be spotted from Earth with the naked eye. This view is two-color composite, where blue represents far-ultraviolet light, and orange is near-ultraviolet light.

Superclusters like Laniakea and Einasto (which is 3 billion light years away) are among the largest structures in the Universe. The discovery of this latest supercluster has been named after Professor Jaan Einasto who was a pioneer in the field of superclusters and celebrated his 95th birthday on 23 February 2024. 

When it comes to visualising the sheer size of these structures imagine an average coin (I really don’t think it matters too much which coin you imagine) on a football pitch. This coin represents the Milky Way Galaxy and the length of the pitch would be the extremities of the supercluster! You might also imagine the Sun as a golf ball and the entire collective mass of the supercluster as Mount Everest in comparison!

A study by MIT physicists suggest the Milky Way’s gravitational core may be lighter in mass, and contain less dark matter, than previously thought. Credits:Credit: ESA/Gaia/DPAC, Edited by MIT News

The announcement came from a group of international astronomers from the Tartu Observatory who also surveyed 662 other superclusters. Their work (which was published in the Astrophysical Journal) also revealed some interesting dynamics inside superclusters for example, they found that the galaxies within a supercluster are receding from each other slower than the general expansion of the universe. This is due to the gravitational pull of the supercluster acting as a brake on the expansion. Whilst it is slowing the expansion of the area it is not slowing it enough to stop the galaxies from drifting apart given enough time. Superclusters should be considered temporary, changing phenomena.

They also found that there was a relationship between the density and size of a supercluster. The relationship was an inverse square relationship meaning that the density of a supercluster decreases with the square of its size. 

Source : Einasto Supercluster: the new heavyweight contender in the universe

The post Astronomers Find the Most Massive Supercluster to Date appeared first on Universe Today.

There are plenty of craters on Mars, especially when compared to Earth. That is primarily thanks to the lack of weathering forces and strong plate tectonics that disrupt the formations of such impacts on our home planet. However, not all impact craters on Mars are directly caused by asteroid impacts. Many of them are caused by the ejecta from an asteroid impact falling back to the planet. One recent study showed how impactful this can be – it concludes that a single large impact crater on Mars created over two billion other smaller craters up to almost 2000 km away.

The study, released at the 55th annual Lunar and Planetary Science Conference in Texas, focuses on a crater called Corinto. It’s located in Elysium Planitia, only about 17 degrees north of the Red Planet’s equator. It’s a relatively young crater by Martian standards, with the scientists’ best estimate of its age being around 2.34 million years ago. It’s pretty massive for being that young, though, as the average time between impacts of its size is around 3 million years. As such, the scientists think it might be the most recent crater of its size on Mars.

That’s not why it’s interesting, though. It has an extensive “ray system”. That means that a significant amount of ejecta was cast out from the impact site and landed elsewhere on the planet, creating “rays” from the central impact point that can be seen on a map of the planet’s surface even today.

A video from JHU APL shows the details of how we understand how impact craters are made.
Credit – JHU APl YouTube Channel

Corinto crater is about 14 km in diameter and 1 km deep. Its interior bowl is pock-marked with other, smaller craters that happened its impact. Indications suggest it was full of water ice when it was hit, as there appeared to be some degassing of the superheated ice after the impact. Calculations point to a relatively steep impact angle of about 30-45 degrees from straight on – and the impactor appeared to be coming from the north.

As a result, much of the ejecta impact field lies to the south, especially the southwest, of the crater. While some secondary ejecta craters are sitting to the north of the main one, it appears clear that the impactor’s angle was significant enough to push most ejecta to the south. 

Tracking the path of this ejecta a few million years later isn’t easy. Scientists used data collected by HiRISE and the Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) and analyzed characteristics of smaller craters surrounding the main Corinto crater. In particular, they looked for craters that looked like they would be caused by ejecta rather than by an interplanetary impactor.

Graphical Depiction of the Facies of Maritan craters around Corinto.
Credit – Golombek et al.

They grouped the different types of ejecta craters they found into five different “facies,” primarily focused on how far away they were from the main crater. Each facies has its distinct characteristics. For example, Facies 0, the one closest to the main crater, are semi-circular, don’t appear to have any ejecta, or have very distinct rims. On the other hand, Facies 3 craters are long and narrow rather than semi-circular (hinting that something rolled through to create them) and have shown up as very bright in the MRO images. 

Two main findings from the paper will probably turn the most heads. The scientists found that there are close to 2 billion secondary impact craters larger than 10 meters caused by the ejecta from Corinto. And those secondary craters appear up to 1850 km away. That would make it, by far, the most impactful (pun intended) of the recent Martian craters in terms of the sheer number and distance of its ejecta. 

The paper didn’t go into what that might mean for our larger understanding of these processes on the red planet, nor what future work might be completed – the version reviewed for this article was only two pages. But, as with most things in science, a new record for something – in this case, distance and amount of secondary impact craters, attracts additional research, so we’ll have to see what if any, future discoveries can be made regarding this interesting Martian crater.

Learn More:
Golombek et al. – CORINTO: A YOUNG, EXTENSIVELY RAYED CRATER THAT PRODUCED A BILLION
SECONDARIES ON MARS
UT – Here’s Something Rare: a Martian Crater That isn’t a Circle. What Happened?
UT – This Crater on Mars is Just a Couple of Years Old
UT – It’s Been Constantly Raining Meteors on Mars for 600 Million Years. Earth too.

Lead Image:
Corinto Crater
Credit – NASA

The post One Impact on Mars Produced More than Two Billion Secondary Craters appeared first on Universe Today.

We are all too familiar of the Moon’s effect on our planet. It’s relentless tug causes our tides but even Mars, which is always at least 55 million kilometres away, can have a subtle effect too. A study has revealed a 2.4 million year cycle in the geological records that show the gentle warming and cooling of our oceans. The records match the interactions between the orbits of Earth and Mars over the longest timescales. These are known as the ‘astronomical grand cycles’ but to date, not much evidence has been found. 

The rhythmical rising and falling of the oceans has been well documented. Even the Sun at an average distance of 150 million kilometres exerts enough of a pull to enhance the effect from the Moon, giving us the spring and neap tides. The Moon’s influence is easy to understand due to its proximity, the Sun’s too due to its enormous mass but Mars is a different story. After all, it’s about half the size of Earth and even at its closest is about 55 million kilometres away. 

It takes two to tango. The moon’s gravity raises a pair of watery bulges in the Earth’s oceans creating the tides, while Earth’s gravity stretches and compresses the moon to warm its interior. Illustration: Bob King

As Earth and Mars orbit around the Sun, their interactions, or rather the gravitational pull from each upon each other are cyclical. These are the astronomical grand cycles and for Earth and Mars they cycle every 2.4 million years.

A paper recently published in Nature Communications reports upon the work of scientists from the University of Sydney and Sorbonne University in France. The team used geological records from the deep sea and to their surprise found a connection between the astronomical grand cycles, global warming patterns and deep ocean circulation. They found a 2.4 million year waxing and waning of deep ocean currents and that seemed to link to increased climate. 

Satellites Detect Deep-Ocean Whirlpools

A definite link emerged but it should be noted that ocean currents are not the only cause of global temperature changes. The current temperature increases have a much stronger link to the human emission of greenhouse gasses.  The paper was authored by Dr Adriana Dutkiewicz and Professor Dietmar Muller from the University of Sydney and Associate Professor Slah Boulila from the Sorbonne University. They reached their conclusion following analysis of the deep-sea sediment records acquired from over half a century of drilling data from hundreds of sites worldwide. The 2.4 million year cycle they found can only have been caused by the interactions between Earth and Mars. 

The interaction of the gravitational field of the two planets means periods of higher incoming solar radiation every 2.4 million years and with it, an increase in global temperatures. Their analysis of the sediments showed breaks in the sedimentary deposits which related to periods of warmer temperatures and more vigorous deep ocean circulation.

The result helps us to understand how deep ocean eddies are key to warming ocean temperatures. Understanding these can help us to understand and model future periods of warming. It may even go some way to mitigate a temporary cessation in ocean currents due to a change in the Atlantic meridional overturning circulation.  This drives the Gulf Stream that helps to keep Europe and other temperature countries the nice warm climate it has become accustomed to. 

 Source : Mars attracts: how Earth’s planetary interactions drive deep-sea circulation

The post Gravity From Mars has an Effect on Earth’s Oceans appeared first on Universe Today.

We, and all other complex life, require stability to evolve. Planetary conditions needed to be benign and long-lived for creatures like us and our multicellular brethren to appear and to persist. On Earth, chemical cycling provides much of the needed stability.

Chemical cycling between the land, atmosphere, lifeforms, and oceans is enormously complex and difficult to study. Typically, researchers try to isolate one cycle and study it. However, new research is examining Earth’s chemical cycling more holistically to try to understand how the planet has stayed in the ‘sweet spot’ for so long.

Earth has supported complex life for hundreds of millions of years, possibly for more than a billion years. This is extremely rare, as far as we can tell. The vast majority of the exoplanets we’ve discovered are not in their stars’ habitable zones. They have very little chance of hosting any life, let alone complex life.

It’s possible that some planets experience a period of stability for much shorter periods of time than Earth. This may describe Mars. It was warm and wet and could’ve hosted simple life, but the planet lost most of its atmosphere and became uninhabitable. Now it’s cold, dry, and dead.

Earth robustly cycles the chemical elements through different systems and has done so for billions of years. Now, about 4.5 billion years after its formation, life is abundant on our precious planet. Biogeochemical cycles like the carbon cycle, the nitrogen cycle, and the methane cycle have allowed the planet to sustain its habitability.

New research published in the Proceedings of the National Academy of Sciences examines these cycles holistically, hoping to better understand the relationships between them. The research is “Balance and imbalance in biogeochemical cycles reflect the operation of closed, exchange, and open sets.” The lead author is Preston Cosslett Kemeny, a University of Chicago TC Chamberlain postdoctoral fellow.

“Overall, this work provides a systematic conceptual framework
for understanding balance and imbalance in global biogeochemical cycles.”

From “Balance and imbalance in biogeochemical cycles reflect the operation of closed, exchange, and open sets.”

Earth’s carbon cycle plays a dominant role in the climate. As carbon accumulates in the atmosphere, the planet warms. As carbon is sequestered into the mantle, the planet cools. Even though it’s been stable for a long time, research shows that small imbalances can upset the system.

What Kemeny and his co-researchers wanted to do was get back to the basics. They wanted to identify a framework for all the reactions, both large and small, that comprise Earth’s chemical cycles. What’s different in their work is that they didn’t specify how they all worked together, if they worked together, or how much they affected one another.

“Our approach provides a new way to identify the fundamental building blocks of stability in the chemical components of Earth’s climate—the underlying ways in which the climate can be stabilized over geological time due to the movement of elements across the ocean, atmosphere, and rock reservoirs,” said Kemeny.

Earth’s long-lasting habitability created the conditions for complex life like us to appear. That habitability is dependent on the complex interplay of chemistry between the ocean, atmosphere and land. This image, captured from the International Space Station 400km above Earth’s surface, shows our planet’s thin atmosphere. Image Credit: NASA

The researchers describe their effort as ‘agnostic’ and explain that it creates “… a systematic and simplified conceptual framework for understanding the function and evolution of global biogeochemical cycles.” They call it agnostic because it doesn’t specify the relationship between environmental conditions and the strength of biogeochemical processes. “By remaining agnostic to the relationships between environmental conditions and the intensity of biogeochemical processes, we sought to recognize and systematize patterns that underly the stability of major element cycles,” Kemeny explains on his website.

“This is an elegant, simplified way to think about an enormous problem, which organizes a lot of previous research on elemental cycles into packages of chemical reactions that can be balanced and understood,” said University of Chicago Assistant Professor Clara Blättler, senior author of the paper.

The complexity of Earth’s cycles makes them difficult to study. They work on long geological timescales, which puts us at a disadvantage. The planet’s carbon cycle illustrates this.

The movement of carbon plays an important role in regulating the planet’s climate. When carbon dioxide accumulates in the atmosphere, the atmosphere traps more heat, which warms up the oceans. However, carbon also creates a weak acid called carbonic acid that breaks rocks down faster. The carbon eventually finds its way to the ocean floor and becomes sequestered in rock. Carbon can also spend some time as part of living things before being sequestered into rock or fossil fuels. This sequestration of carbon eventually cools the planet but takes millions of years. Carbon is eventually returned to the atmosphere by volcanoes and by the burning of fossil fuels.

The Carbon cycle plays a dominant role in moderating Earth’s climate, but other chemical cycles influence it. Image Credit: U.S. DOE, Biological and Environmental Research Information System.

Trying to understand the carbon cycle is made more difficult by its interaction with other cycles. The Earth’s cycles also aren’t static. They change over time, adding to the complexity. There are also missing pieces from the large puzzle of Earth’s cycles. Researchers are forced to make assumptions to fill in the blanks.

Kemeny devotes much of his time to understanding Earth’s cycles, and he and his colleagues hope that their approach can yield better results. “Models of global element cycles seek to understand how biogeochemical processes and environmental conditions interact to sustain planetary habitability,” Kemeny writes on his website. “However, outcomes from such models often reflect specific interpretations of geochemical archives.”

The researchers think their approach may help overcome the obstacles to understanding Earth’s cycles. They employed a mathematical analysis to develop a framework identifying all of the major and minor cycles that contribute to Earth’s long-term habitability by balancing the carbon cycle.

The result was a new, more holistic way to look at Earth. The climate can be represented by a large set of interconnected chemical equations. These equations must balance over certain time periods to keep the carbon cycle stable and the Earth habitable.

The Sulphur Cycle is just one of Earth’s important cycles. It moves sulphur between rocks, water, and living things. Kemeny and his colleagues are trying to understand all of Earth’s cycles holistically rather than in isolation. Image Credit: By Bantle – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=20411832

Kemeny highlights one episode in Earth’s climate history to illustrate the point. The Cenozoic era began about 65.5 million years ago and is the era we live in now. The Cenozoic is a long-term cooling trend in Earth’s history, and the period that preceded it was a greenhouse climate. Kemeny and his colleagues say that their holistic approach can open a window into how the climate changed.

“For example, say that you are considering a hypothesis for why the climate changed in the past – such as the major cooling of the last 65 million years,” Kemeny said. “You can take this framework and use it to say: well, if X process increased or decreased, then it should have also caused Y to happen, or would have needed to be balanced by Z, and that you have to account for those outcomes—so with that prediction we can look for evidence for the joint operation of the whole geochemical system.”

Astrobiology and planetary habitability are key topics in space science. With the help of the JWST and other upcoming observatories and telescopes, scientists are getting a look at the atmospheres of distant exoplanets. But it’s a difficult process, made more difficult by our less-than-complete understanding of our own planet’s habitability. Understanding our own planet can help us better understand exoplanets.

But there’s a certain type of joy in understanding Earth for its own sake, and this new holistic approach should grow our understanding.

“We hope it’s a beautiful way to help understand all the chemistries that are involved in making Earth a safe place for life to evolve,” Blättler said.

“Overall, this work provides a systematic conceptual framework for understanding balance and imbalance in global biogeochemical cycles,” the authors conclude.

The post Earth’s Long-Term Habitability Relies on Chemical Cycles. How Can We Better Understand Them? appeared first on Universe Today.

Universe Today has examined the importance of studying impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, and planetary atmospheres, and how these intriguing scientific disciplines can help scientists and the public better understand how we are pursuing life beyond Earth. Here, we will look inward and examine the role that planetary geophysics plays in helping scientists gain greater insight into our solar system and beyond, including the benefits and challenges, finding life beyond Earth, and how upcoming students can pursue studying planetary geophysics. So, what is planetary geophysics and why is it so important to study it?

“Planetary geophysics is the study of how planets and their contents behave and evolve over time,” Dr. Marshall Styczinski, who is an Affiliate Research Scientist at the Blue Marble Space Institute of Science, tells Universe Today. “It is essentially the study of What Lies Below, focusing on what we can’t see and how it relates to what we can see and measure. Most of the planets (including Earth!) are hidden from view—geophysics is how we know everything about the Earth below the deepest we have dug down!”

As its name implies, geophysics is the study of understanding the physics behind geological processes, both on Earth and other planetary bodies, with an emphasis on interior geologic processes. This is specifically useful for planetary bodies that are differentiated, meaning they have several interior layers resulting from heavier elements sinking to the center while the lighter elements remain closer to the surface. 

The planet Earth, for example, is separated into the crust, mantle, and core, with each having its own sub-layers, and understanding these interior processes help scientists piece together what the Earth was like billions of years ago and even make predictions regarding the planet’s environment in the far future. These interior processes drive the surface processes, including volcanism and plate tectonics, both of which are responsible for maintaining the Earth’s temperature and recycling materials, respectively. So, what are some of the benefits and challenges of studying planetary geophysics?

Dr. Styczinski tells Universe Today, “Geophysics gives us the tools to determine what exists beneath the visible surface of planetary bodies (planets, moons, asteroids, etc.). It’s our only way to learn about what we can’t see! Finding out what is inside a planet, and under what conditions, like how much pressure and heat for each layer, helps us build a history for the planet and know how it will continue to change over time.”

In contrast, Dr. Styczinski also emphasizes to Universe Today the challenges, noting the difficulty in reproducing geologic conditions that occur over millions of years, even with the most sophisticated laboratories in the world, due to their slow movements over vast amounts of time. Additionally, he notes that particle accelerators are sometimes required to reproduce the extreme conditions within gas giants, which are also differentiated, though with gas and liquid layers, as opposed to rock. 

Artist’s illustration of gas giant interiors. (Credit: NASA/Lunar And Planetary Institute)

But Earth is not the only rocky world in our solar system that exhibits differentiation, as all four rocky planets (Mercury, Venus, Earth, and Mars) exhibit some form of interior layering that has occurred over billions of years, though at smaller scales due to their sizes. In addition to the planets, many rocky moons throughout the solar system also exhibit differentiation, including Jupiter’s Galilean moons, Io, Europa, Ganymede, and Callisto, and several of Saturn’s moons, including Titan, Enceladus, and Mimas. Of those moons, Europa, Titan, and Enceladus are currently targets for astrobiologists, as Europa and Enceladus have been confirmed to possess interior liquid water oceans, with Titan presenting strong evidence, as well. Additionally, Titan is the only moon with a dense atmosphere, and like Earth, it likely has interior geophysics driving it. But what can planetary geophysics teach us about finding life beyond Earth?

Artist’s illustration of terrestrial (rocky) planet interiors. (Credit: NASA) Artist’s illustration of the interior of Jupiter’s icy moon, Europa. (Credit: NASA/JPL-Caltech/Michael Carroll) Artist’s illustration of the interior of Saturn’s icy moon, Enceladus. (Credit: NASA/JPL-Caltech)

“We’ve learned from studying Mars that the surfaces of planets can be quite hostile to life as we know it,” Dr. Styczinski tells Universe Today. “If and when we are able to find life elsewhere in the solar system that we didn’t bring there ourselves, it will probably be found beneath the surface, where it can be protected from the harsh environment at the surface. Geophysics gives us the means to plan for expeditions into the subsurface, and the only method of finding liquid water that’s hidden from view on icy moons. These are the best places we know of to look for life beyond Earth.”

The reason why the surface of Mars is inhospitable to life as we know it is due to its lack of a thick atmosphere, which is responsible for preventing the Sun’s charged particles in the solar wind from reaching the planetary surface. While Mars once had a powerful magnetic field, Dr. Styczinski notes to Universe Today that “Some researchers think magnetic fields can actually strip away the atmosphere”, while quickly noting this “is a topic of fierce debate.” Mars once had a thicker atmosphere, which was lost along with its magnetic field over billions of years as the Red Planet’s interior cooled.

In addition to our solar system, Dr. Styczinski tells Universe Today that planetary geophysics also does an excellent job of helping scientists better understand exoplanets, specifically multi-planet systems like our own. While no exoplanet surface has yet been imaged, better understanding the geophysical processes of planetary bodies within our solar system helps scientists gain insights into how these same processes could occur on planets throughout the cosmos, including the magnetic field, as well. 

A planet’s magnetic field is driven by the internal processes occurring in its outer core, which for Earth is comprised of churning, liquid metal fluid, whereas the inner core is a solid ball of compressed metal. As this outer core’s fluid churns and circulates, it creates electrical currents that produce the massive magnetic field that envelopes our small, blue world in a bubble of protection from harmful space weather. The Earth’s magnetic field traps charged particles in radiation belts in space nearby. The way the magnetic field protects our planet can be seen during magnetic storms from the Sun, when the magnetosphere bends and flexes in response, sending particles from these radiation belts close to the surface in the high northern and southern latitude regions. There, they interact with the Earth’s atmosphere to produce the breathtaking auroras often observed in Alaska, the Nordic countries, and Antarctica. 

Rendition displaying the solar wind interacting with Mars, which does not possess a magnetic field, versus Earth and its very active magnetic field. The lack of a magnetic field means Mars is constantly bombarded by space weather, exposing its surface to harmful radiation, whereas Earth’s surface is almost entirely protected, allowing life to both survive and thrive across the planet. (Credit: NASA)

However, while the Earth’s magnetic field is impressive, it’s only fitting that the largest planet in the solar system, Jupiter, equally has the largest magnetic field, whose “tail” extends as far as Saturn’s orbit, or approximately 400 million miles. Additionally, the internal processes responsible for generating magnetic fields on gaseous planets like Jupiter, Saturn, Uranus, and Neptune could be starkly different than on Earth. Therefore, given all of these variables and processes, what is the most exciting aspect of planetary geophysics that Dr. Styczinski has studied during his career?

“The part of planetary geophysics that I find the most exciting is using the invisible magnetic field to sense subsurface oceans,” Dr. Styczinski tells Universe Today. “I continue to be blown away by how it all works when I really think about it. Salty ocean waters partially reflect the fields they are exposed to from their parent planet, as in Jupiter and its moon Europa. We use these measurements along with laboratory studies here on Earth and geophysics to understand the material layers inside Europa to work out the properties of the ocean. It still blows my mind that this process works as well as it does.”

Like most scientific fields, planetary geophysics encompasses a myriad of scientific disciplines and backgrounds with the goal of answering the universe’s toughest questions through constant collaboration and innovation. Geophysics is a combination of geology and physics but also incorporates mathematics, chemistry, atmospheric science, seismology, mineralogy, and many others with the goal of better understanding the interior processes of the Earth and other planetary bodies throughout the solar system and beyond. Therefore, what advice can Dr. Styczinski offer upcoming students who wish to pursue studying planetary geophysics?

“There are many paths into geophysics, and many different things to study and ways to study them,” Dr. Styczinski tells Universe Today. “Your past studies don’t have to be specific to geophysics or even involve geology at all. Perhaps the most productive move you can make is to ask for help, especially from someone studying a topic that interests you. Computer programming skills are invaluable. I recommend learning Python—it’s free and widely used all across science. There are many tutorials available, also for free. While not all geophysics will require a lot of programming, I think all geophysicists will benefit from having those skills.”

How will planetary geophysics help us better understand our place in the cosmos in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

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Quasars are the brightest objects in the Universe. The most powerful ones are thousands of times more luminous than entire galaxies. They’re the visible part of a supermassive black hole (SMBH) at the center of a galaxy. The intense light comes from gas drawn toward the black hole, emitting light across several wavelengths as it heats up.

But quasars are more than just bright ancient objects. They have something important to show us about the dark matter.

Large galaxies have supermassive black holes at their centers. Even those only casually familiar with space know that black holes can suck everything in, even light. But as black holes draw nearby gas towards themselves, the gas doesn’t all go into the hole, past the event horizon and into oblivion. Instead, much of the gas forms a rotating accretion disk around the black hole.

SMBHs aren’t always actively drawing material to them, an act known as ‘feeding.’ But when an SMBH is actively feeding, it’s called an active galactic nucleus (AGN.) When the material in the disk rotates, it heats up. As it heats, it emits different wavelengths of electromagnetic radiation. It can also emit jets.

When astronomers first began to detect this light, they only knew they were seeing objects that emitted radio waves. The name quasar means quasi-stellar radio source. But as time went on astronomers learned more, and the term active galactic nucleus was adopted. The term quasar is still used, but they’re now a sub-class of AGN that are the most luminous AGN.

Quasars inhabit galaxies that are surrounded by enormous haloes of dark matter. Astronomers think there’s a link between the dark matter haloes (DMH) and the quasars. The DMH may direct more matter toward the center of the galaxy, feeding the SMBH and igniting a quasar, and even aiding the formation of more massive galaxies.

Artist rendering of the dark matter halo surrounding our galaxy. Credit: ESO/L. Calçada

A team of researchers has created a new catalogue of quasars that will be a powerful tool for probing quasars, DMHs, and SMBHs. Their results are in a new paper in The Astrophysical Journal titled “Quaia, the Gaia-unWISE Quasar Catalog: An All-sky Spectroscopic Quasar Sample.” The lead author is Kate Storey-Fisher, a postdoctoral researcher at the Donostia International Physics Center in Spain.

“This quasar catalogue is different from all previous catalogues in that it gives us a three-dimensional map of the largest-ever volume of the universe,” said map co-creator David Hogg, a senior research scientist at the Flatiron Institute’s Center for Computational Astrophysics in New York City and a professor of physics and data science at New York University. “It isn’t the catalogue with the most quasars, and it isn’t the catalogue with the best-quality measurements of quasars, but it is the catalogue with the largest total volume of the universe mapped.”

This infographic helps explain Quaia, the new catalogue of 1.3 million quasars. Image Credit: ESA/Gaia/DPAC; Lucy Reading-Ikkanda/Simons Foundation; K. Storey-Fisher et al. 2024

The fact that the new catalogue captures the largest total volume of the Universe mapped and all the quasars in that space is key to understanding its purpose. It’s not meant as a survey that captures the largest number of quasars. The catalogue is meant to be a tool astrophysicists can use to understand the relationships between quasars, dark matter, black holes, and galaxies.

They call their catalogue Quaia because the data comes from the ESA’s Gaia spacecraft. Gaia’s mission is to map about one billion objects in the Milky Way, mostly stars. And it’s going about its mission with extreme accuracy. But among the multitudes of stars Gaia has mapped is a large number of quasars well beyond the Milky Way. That generated the name “Quaia.”

“We were able to make measurements of how matter clusters together in the early universe that are as precise as some of those from major international survey projects — which is quite remarkable given that we got our data as a ‘bonus’ from the Milky Way–focused Gaia project,” Storey-Fisher says.

Dark matter tends to clump in haloes around galaxies, and studying the distribution of quasars can help explain the distribution of dark matter. In the large scale of the Universe, dark matter is organized as a web, and the catalogue of quasars helps map that web.

The Cosmic Microwave Background (CMB), a strong piece of evidence for the Big Bang, is also part of this. As the light from the CMB travels toward us through space, the dark matter web’s massive gravitational power bends the light. Scientists can compare the CMB light we receive with the map of quasars and compare the two. The comparisons will them about the relationship between dark matter and quasars and how matter clumps together in the Universe.

Since quasars trace the cosmic web, their distribution gives information about the web that other sources can’t. For example, it can trace the distribution of matter at higher redshifts than galaxies can. And since it’s space-based, it avoids some of the data contamination that other quasar surveys suffer from, such as the Sloan Digital Sky Survey (SDSS.)

This is not the first quasar map/catalogue to be created. There are several others, including one from the Sloan Digital Sky Survey.

This figure shows five different quasar maps created by scientists using different data and methodologies. The creators of Quaia say that its redshifts are more accurate than the others, along with other properties. Image Credit: K. Storey-Fisher et al. 2024

As the animation below shows, Quaia is more complete than the SDSS’s DR16Q, the SDSS’s quasar catalogue that accompanied its data release 16.

via GIPHY

Though the Gaia mission itself doesn’t generate many of its own headlines, it’s at the foundation of modern space science. Its data is behind lots of published research.

“This quasar catalogue is a great example of how productive astronomical projects are,” says Hogg. “Gaia was designed to measure stars in our own galaxy, but it also found millions of quasars at the same time, which give us a map of the entire universe.”

Now, the new Quaia catalogue is playing a similar role. The data it contains is already being used by other researchers.

“It has been very exciting to see this catalogue spurring so much new science,” Storey-Fisher says. “Researchers around the world are using the quasar map to measure everything from the initial density fluctuations that seeded the cosmic web to the distribution of cosmic voids to the motion of our solar system through the universe.”

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The exoplanet census now stands at 5,599 confirmed discoveries in 4,163 star systems, with another 10,157 candidates awaiting confirmation. So far, the vast majority of these have been detected using indirect methods, including Transit Photometry (74.4%) and Radial Velocity measurements (19.4%). Only nineteen (or 1.2%) were detected via Direct Imaging, a method where light reflected from an exoplanet’s atmosphere or surface is used to detect and characterize it. Thanks to the latest generation of high-contrast and high-angular resolution instruments, this is starting to change.

This includes the James Webb Space Telescope and its sophisticated mirrors and advanced infrared imaging suite. Using data obtained by Webb‘s Near-Infrared Camera (NIRCam), astronomers with the MIRI mid-INfrared Disk Survey (MINDS) survey recently studied a very young variable star (PDS 70) about 370 light-years away with two confirmed protoplanets. After examining the system and its extended debris disk, they found evidence of a third possible protoplanet orbiting the star. These observations could help advance our understanding of planetary systems that are still in the process of formation.

The MINDS survey is an international collaboration consisting of astronomers and physicists from the Max-Planck-Institute for Astronomy (MPIA), the Kapteyn Astronomical Institute, the Space Research Institute at the Austrian Academy of Sciences (OAW-IFW), the Max-Planck Institute for Extraterrestrial Physics (MPE), the Centro de Astrobiología (CAB), the Institute Nazionale di Astrofisica (INAF), the Dublin Institute for Advanced Studies (DIAS), the SRON Netherlands Institute for Space Research, and multiple universities. The paper that describes their findings will appear in the journal Astronomy & Astrophysics.

This spectacular image from the SPHERE instrument on ESO’s Very Large Telescope is the first clear image of a planet caught in the very act of formation around the dwarf star PDS 70. Credit: ESO/A. Müller et al.

PDS 70 has been the subject of interest in recent years due to its young age (5.3 to 5.5 million years) and the surrounding protoplanetary disk. Between 2018 and 2021, two protoplanets planets were confirmed within the gaps of this disk based on direct imaging data acquired by sophisticated ground-based telescopes. This included the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) and GRAVITY instruments on the ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA).

In recent years, the MINDS team has used Webb spectral data to perform chemical inventories on protoplanetary disks in multiple star systems. In a previous study based on data from Webb‘s Mid-Infrared Instrument (MIRI), the MINDS team detected water in the inner disk of PDS 70, located about 160 million km (100 million mi) or 1.069 AU from the star, a find that could have implications for astrobiology and the origins of water on rocky planets (like Earth). These results showcased Webb’s impressive capabilities and how it can observe the cosmos in infrared (IR) wavelengths inaccessible to ground-based observatories.

Valentin Christiaens, an F.R.S-FNRS Postdoctoral Researcher at the University of Liège and KU Leuven, was the lead author of this latest paper. “The advantage of Webb’s instruments is that they observe at infrared wavelengths that cannot be observed from the ground because of our atmosphere, which absorbs most of the infrared spectrum,” he told Universe Today via email. “Thanks to Webb we can obtain measurements of planets in formation (called protoplanets) in infrared, which allow us to better constrain our models of planet formation.”

For their latest study, the MINDS team examined PDS 70 using data from Webb‘s NIRCam as part of the MIRI Guaranteed Time Observations program on planet formation. Christiaens and his team were motivated to study PDS 70 further because previous research indicated the possible detection of a third protoplanet. This makes the system an ideal laboratory to study planet-disk interactions and search for accretion signatures. The presence of a possible third signal was detected in 2019 by a team using the VLT/SPHERE instrument but remained unconfirmed since.

This artist’s illustration shows a compact protoplanetary disk and an extended one. Credit: NASA, ESA, CSA, Joseph Olmsted (STScI)

One possible interpretation for this signal was that it traces a third planet. Using NIRCam data, Christiaens and his colleagues sought to redetect this signal and confirm that it was a third planet in the system. The JWST is especially well-suited to this task, thanks to its advanced optics and coronograph, which removes interference from Webb’s images by blocking the star’s light. He and his colleagues were also aided by advanced algorithms that help separate starlight from other point sources in orbit (like exoplanets) and debris disks. As Christiaens explained:

“The observation of another star, called a reference star, can be used to subtract the light from the star of interest and look for exoplanets there. In our study, we instead opted for a technique called “roll subtraction,” where two sequences of images are taken of the star of interest before and after the instrument is rotated, respectively, so that the position of an exoplanet has rotated in the two image sequences. From there, by subtracting the images of one sequence from those of the other, and vice versa, we can effectively get rid of the light of the star and make images of its environment – planets and disk.”

The team then combined their measurements with previous observations made with ground instruments and compared them to planetary formation models. From this, they could deduce the quantity of accumulated gas and dust around the protoplanet during the observation period. The quality of the images also allowed them to highlight a spiral arm of gas and dust supplying the second confirmed candidate (PDS 70 c), as predicted by the models. Lastly, they detected a bright signal consistent with a protoplanet candidate enshrouded in dust.

“What makes this candidate so interesting is that it could be in 1:2:4 resonance with planets b and c, already confirmed in the system (i.e., its orbital period will be almost exactly two times and four times shorter than that of b and c, respectively),” said Christiaens. This is precisely what happens with three of Jupiter’s Galilean Moons (Ganymede, Europa, and Io), which are also in a 1:2:4 resonance. The possibility of a star system with three planets in this orbital relationship would be a gold mine for astronomers. “However, more observations are needed before this resonance can be confirmed,” Christiaens added.

The evolutionary sequence of protoplanetary disks with substructures, from the ALMA CAMPOS survey. These wide varieties of planetary disk structures are possible formation sites for young protoplanets. Image Credit: Hsieh et al. in prep.

In addition to demonstrating Webb’s capabilities, these findings could help inform our current understanding of how planetary systems form and evolve. This is one of the main objectives of the JWST: to use its advanced infrared optics to probe young star systems where planets are still in the process of forming. This has been a high priority for astronomers ever since Kepler began detecting exoplanets that defied widely accepted theories of how planetary systems form and evolve. In particular, the detection of many gas giants orbiting closely to their suns (“Hot-Jupiters”) contradicted theories that gas giants form in the outer reaches of star systems.

By observing young star systems at different stages of formation, astronomers hope to test various theories about how the Solar System came to be. As Christiaens summarized:

“The migration of planets is thought to play a crucial role in the evolution of planetary systems and helps explain the diversity of systems found to date via indirect methods. In many mature systems, planets have been found to resonate with each other, suggesting that this migration did indeed take place in the past. In our case, we observe a very young system, still in formation, where the 2 known giant planets seem to be in resonance and where the third potential planet, if confirmed, would also be with the other two. In the case of the Solar System, we suspect that the migration and resonance capture of the giant planets probably also took place a very long time ago, [which could] explain their current configuration (Great Tack hypothesis). Here we are potentially observing it live in another system!”

Further Reading: arXiv

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In the 1960s, NASA engineers developed a series of small lifting-body aircraft that could be dropped into the atmosphere of a giant planet, measuring the environment as they glided down. Although it would be a one-way trip to destruction, the form factor would allow a probe to glide around in different atmospheric layers, gathering data and transmitting it back to a parent satellite. An updated version of the 1960s design is being tested at NASA now, and a drop-test flight from a helicopter is scheduled for this month.

“We are looking to take an idea to flight and show that a lifting body aircraft can fly as a probe at this scale – that it can be stable, that components can be integrated into the probe, and that the aircraft can achieve some amount of lift,” said John Bodylski, the principal investigator at NASA’s Armstrong Flight Research Center in Edwards, California. Bodylski is working to prove that a lifting body aircraft design could meet the requirements for an atmospheric probe that could be used at giant planets, like Uranus or Jupiter.

Robert “Red” Jensen removes a major component from an aircraft mold for assembly of a prototype of an atmospheric probe as Justin Hall watches at NASA’s Armstrong Flight Research Center in Edwards, California. Credit: NASA/Steve Freeman

The idea behind the concept is that a lifting body aircraft relies on its unique blunt shape for lift, rather than wings. Bodylski and his team have designed two lifting body aircraft, both of which are about 70 cm (27 1/2 inches) long, and 60 cm (24 inches) wide. One is almost built and ready for flight.

NASA has a long history of doing flight tests with lifting bodies. From 1963 to 1975, NASA tested several designs to demonstrate the ability of pilots to maneuver and safely land a wingless vehicle. These vehicles included the M2-F1, M2-F2, HL-10, X-20, X-24A, and the X-24B. These lifting bodies were designed to validate the concept of flying a wingless vehicle back to Earth from space and landing it like an aircraft. The concept was influential in designing the Space Shuttle.

While the Space Shuttle and other human-carrying lifting body vehicles had inherent issues, even back in the 1960’s planetary scientists realized the concept could be more feasible for smaller uncrewed probes.

NASA says that current small atmospheric probes such as CubeSats, gather and transmit data for about 40 minutes and can take in approximately 10 data points before their parent satellite is out of range. Bodylski estimates this lifting body design could descend more rapidly and at a steeper angle, collecting the same information in 10 minutes, plus gather additional data for another 30 minutes from much deeper in a thick atmosphere.

The lifting body aircraft on Rogers Dry Lake, near what is now NASA’s Armstrong Flight Research Center in Edwards, California, include, from left, the X-24A, the M2-F3, and the HL-10. Credit: NASA

Lifting bodies have been in and out of vogue for decades. NASA actually had two designs for lifting bodies in the running as a precursor and later a successor to the Space Shuttle. The Dyna Soar was based on NASA’s X-20 lifting body and was designed to be launched by rocket into orbit, and the lifting body design would have allowed it to land like an airplane. Due to due to high costs, changing priorities for both the military and NASA – with the Apollo program just getting going — the Dyna Soar program was cancelled in December 1963, just before the first crewed test flight was scheduled for the following year.

Later, in 1996 NASA selected Lockheed Martin to build and fly the X-33 test vehicle to demonstrate advanced technologies for a new reusable spaceplane vehicle to succeed the Space Shuttle. Called VentureStar, it would have been a single-stage-to-orbit vehicle. However, NASA cancelled the project in 2001 before any test flights were carried out after some technical problems proved too difficult to solve.

More info on Bodylski’s project.

The post Improving a 1960s Plan to Explore the Giant Planets appeared first on Universe Today.

Not long after the explosion of Supernova 1987a, astronomers were abuzz with predictions about how it might look in a few years. They suggested a pulsar would show up soon and many said that the expanding gas cloud would encounter earlier material ejected from the star. The collision would light up the region around the event and sparkle like diamonds.

Today, astronomers look at the site of the stellar catastrophe and see an expanding, glowing ring of light. Over the years, its shape has changed to a clumpy-looking string of pearls. What’s happening to affect its appearance? The answer lies in something called the “Crow Instability.” We see this aerodynamical process when vortexes off the wingtips of airplanes interact with the contrails from their engines. The instability breaks up the contrail into a set of vortex “rings”.

University of Michigan graduate student Michael Wadas says this type of instability could explain why Supernova 1987a formed a string of pearls. “The fascinating part about this is that the same mechanism that breaks up airplane wakes could be in play here,” said Wadas, who is now doing post-graduate work at CalTech. If that’s true, it will go a long way toward explaining why those ghostly pearls exist.

The expanding ring-shaped remnant of SN 1987A and its interaction with its surroundings, seen in X-ray and visible light. The star that became SN 1987a expelled concentric rings of material during its red and blue supergiant phases, and the shockwave from the supernova lit them up. Image: Public Domain, https://commons.wikimedia.org/w/index.php?curid=278848 About 1978a and its String of Pearls

Light and neutrinos from Supernova 1987a reached Earth on February 23, 1987. The original star, Sanduleak -69 202, lay about 168,000 light-years away in the Large Magellanic Cloud. It exploded as Type II, the first one in modern times to show astronomers the details of a core-collapse supernova. Since then, astronomers watched as a ring of ejected material and a shockwave from the explosion itself spread to space. It slammed into the material shed earlier in the star’s life. It does have a neutron star in the center. Astronomers detected it in 2019 and observed it using X-ray and gamma-ray observatories.

Several months after the explosion, astronomers used the Hubble Space Telescope to image bright rings surrounding the explosion site. That material came from the stellar wind of the progenitor star. Ultraviolet light from the explosion ionized the gases in the cloud. The inner ring lay about 2/3 of a light-year from the original star. The expanding ejecta from the supernova eventually collided with it in 2001. That heated it further. The shockwave has now expanded beyond the rings, leaving behind pockets of warm dust and glowing clouds of gas. The turbulence of that shockwave and the damage it did to regions of the inner ring is created the “pearls”.

Competing Theories for the String

So, what physics underlies the appearance of the pearls? Astronomers have tried to explain the string using something called a Rayleigh-Taylor instability. That occurs when two fluids (or plasmas) of different densities interact with each other. Think of oil and water trying to mix, or a heavy pyroclastic flow streaming out of a volcano. The interaction forms interesting and predictable shapes in the fluids. For 1978a, the denser “fluid” is the material ejected during the supernova explosion. It is colliding with a less dense cloud of material ejected earlier that has spread out to space. However, there are issues with using the Rayleigh-Taylor instability to explain what we see at the supernova site.

A simulation shows the shape of the gas cloud on the left and the vortices, or regions of rapidly rotating flow, on the right. Each ring represents a later time in the evolution of the cloud. The gas cloud starts as an even ring with no rotation. It becomes a lumpy ring as the vortices develop. Eventually, the gas breaks up into distinct clumps. Credit: Michael Wadas, Scientific Computing and Flow Laboratory

“The Rayleigh-Taylor instability could tell you that there might be clumps, but it would be very difficult to pull a number out of it,” said Wadas, who suggested the Crow Instability in a paper just published in Physical Review Letters. Jet contrails are a better comparison because the wingtip vortices break up the long smooth line of a jet contrail. The vortices flow into each other, leaving gaps that can be predicted.

To explore that idea, Wadas and his colleagues simulated the way winds push a model cloud outward while also dragging on its surface. The top and bottom of the cloud got pushed out faster than the middle. That caused it to curl in on itself, triggering a Crow Instability that broke the cloud apart into 32 even clumps similar to the string of pearls at 1987a (which has 30-40 clumps). That predictable number of clumps is why the team suggested the Crow Instability as a formation agent for the string. They also think it could help predict the formation of more beaded rings around the explosion site or when dust around a star coalesces to form planets. Recent JWST infrared images seem to show even more clumps that have appeared in the ring, and it will be interesting to see if more of them appear in the future.

For More Information

Explaining a Supernova’s “String of Pearls”
Hydrodynamic Mechanism for Clumping along the Equatorial Rings of SN1987A and Other Stars

The post Finally, an Explanation for the “String of Pearls” in Supernova 1987A appeared first on Universe Today.

No matter what mode of transportation you take for a long trip, at some point, you’ll have to refuel. For cars, this could be a simple trip to a gas station, while planes, trains, and ships have more specialized refueling services at their depots or ports. However, for spacecraft, there is currently no refueling infrastructure whatsoever. And since the fuel spacecraft use must be stored cryogenically, and the tanks the fuel is stored in are constantly subjected to the thermal radiation from the Sun, keeping enough fuel in a tank for a trip to Mars with astronauts is currently infeasible. Luckily, NASA is currently working on it and recently released a detailed look at some of that work on a blog on their website.

The problem definition is very clear – cryogenic hydrogen and oxygen are used as fuel on most spacecraft missions. Once in space, the tanks the fuel is stored in heat up due to the constant solar radiation they’re subjected to. Since there’s no air, there’s no way to radiate out that heat, so eventually, it can get through even the most sophisticated passive thermal insulation system. When it does, the fuel starts to boil, and mission planners typically have chosen to eject the vaporous fuel out into space rather than leaving it as a potential medium to heat the rest of the fuel faster.

This resultant fuel lost to this sublimation can cost as much as half of the cryogenic fuel needed for a 3-year mission to Mars – in just a single year. In short, crewed trips to Mars are impossible using the current fuel storage technology in space. However, there are alternatives, known as Zero Boil-Off (ZBO) or Reduced Boil-Off (RBO) systems. These advanced tanks use a combination of “active” processes to maintain tank pressure and not allow too much loss of fuel during long space flights.

Fraser makes an argument for why refueling is so critical.

An “active” process must be actively controlled and typically requires some sort of power input. In particular, ZBO systems rely on two technology ideas – a jet mixing of the propellant and a droplet injection technology. Let’s take a look at the mixing technology first.

In this example, part of the fuel would be forcibly mixed back into the vapor space in a particular way that would allow it to control the phase changes of the vapor/fuel interface. In essence, it would stop the fuel from sublimating into a vapor in the first place. Similarly, a droplet injection system would use a novel type of spray bar to inject fuel droplets into the vapor area, causing it to condense and remove some of the pressure from the system.

To add another layer of complexity to these already complicated fluid dynamics systems, this all must be done in microgravity, where things like droplet formation and liquid mixing don’t always happen the same way as they do on Earth. So, NASA decided to do what it does best and run some experiments – in this case on the ISS.

Image of the ZBOT-1 experiment being installed on the ISS by astronaut Joseph Acaba.
Credit – NASA

Back in 2017, NASA started the ZBOT-1 Experiment on the ISS. It was intended to quantify how the jet mixing would behave in microgravity, and the result of some 30+ tests was that we still understand very little about how these systems work in microgravity. While how they were is different than what most fluid engineers are used to, they are still acting according to physical laws, so more experiments would help narrow down the models that tank designers can use to understand how these ZBO systems might best be used.

Two other experiments are focused on furthering that understanding – one called the ZBOT-NC Experiment, is due to be launched to the ISS in 2025. It will study the effects of microgravity on “non-condensable gases,” which can be used to control the pressure inside the fuel tank. Data from its observations can also be fed into the CFD models, allowing scientists to understand better how the model differs from reality in microgravity.

The final test in the series will focus on droplet phase changes. Known as the ZBOT-DP test, this is the most ambitious of the three, as it tests a technology that has never been used in microgravity at all before. It will focus on understanding how droplets interact with their surroundings, including superheated tank walls, in microgravity environments. They could eventually lead to a fully functional droplet system and an active control system to ensure no tank boil-off happens.

The idea of in-space refueling has been around for a long time, as this VideoFromSpace feature shows.
Credit – VideosFromSpace YouTube Channel / NASA Technology

That’s still a long way off those, with no planned date for the ZBOT-DP test. Given the importance of this technology to missions like the crewed Artemis mission planned in the next few years, it seems that the successful completion of these experiments and the design and testing of a fully ZBO fuel tank should be very high on NASA’s priority list. While the agency’s already supporting it, let’s hope that the researchers involved can prove their ideas before they’re needed for a real human mission.

Learn More:
NASA – Zero-Boil-Off Tank Experiments to Enable Long-Duration Space Exploration
UT – Why Build Big Rockets at All? It’s Time for Orbital Refueling
UT – There’s Now a Gas Station… In Space!
UT – Robotics Refueling Research Scores Huge Leap at Space Station

Lead Image:
The Gateway space station—humanity’s first space station around the Moon—will be capable of being refueled in space.
Credits: NASA

The post NASA is Working on Zero-Boil Off Tanks for Space Exploration appeared first on Universe Today.

A twinset of icy asteroids called Mors-Somnus is giving planetary scientists some clues about the origin and evolution of objects in the Kuiper Belt. JWST studied them during its first cycle of observations and revealed details about their surfaces, which gives hints at their origins. That information may also end up explaining how Neptune got to be the way it is today.

The Mors-Somnus binary is part of a collection of objects beyond Neptune. They’re called, aptly enough, “Trans-Neptunian Objects” or TNOs, for short. About 3,000 are numbered and known, and many more aren’t yet surveyed. They all lie beyond the orbit of Neptune and are divided into various classes. There are the classical Kuiper Belt Objects (KBOs) and scattered disc objects. Within those two classes, there are resonant TNOs—which move in resonance with Neptune and extreme TNOs, which orbit far beyond Neptune (around 30 AU). Then there are objects in orbits similar to Pluto’s, called “plutinos”. Mors-Somnus is also a Plutino.

The orbit of Mors-Somnus with respect to Neptune in the outer Solar System. Courtesy JPL. Neptune and Beyond

Why is there such a varied bunch of objects “out there”? Where did they originate and how have they changed over time? One way to answer those questions is to study the surface properties of Kuiper Belt Objects and, in particular, icy rocks like Mors-Somnus. One way to do that is to take spectra of their surfaces. The data reveals information about the surface compositions of these objects. That, in turn, tells scientists something about the environments in which they formed and those they’ve experienced over time.

Neptune itself likely formed closer to the Sun but then migrated to the outer Solar System (along with Jupiter, Saturn, and Uranus). At the same time, a huge dense disk of rocky and icy planetesimals and asteroids populated space out to about 35 AU. As the giant planets migrated to more distant orbits, they preferentially scattered those smaller bodies. These icy asteroids and cometary bodies settled into the Kuiper Belt, scattered disk, and the Oort Cloud. How that activity progressed and where those icy bodies came from in the first place are questions planetary scientists are working to answer.

More About Mors-Somnus and Neptune

This is where Mors-Somnus comes in handy. The pair is a good example of a “cold classical” TNO. It was studied by JWST as part of a program called Discovering the Surface Compositions of Trans-Neptunian Objects (DiSCO-TNOs) led by Ana Carolina de Souza Feliciano and Noemí Pinilla-Alonso at the University of Central Florida. The project identifies the unique spectral properties of these small celestial bodies beyond Neptune, something that hasn’t been done before now.

An artist’s conception of Mors-Somnus, a binary duo — a pair of icy asteroids bound by gravity, is shown. These lie just beyond the orbit of Neptune. JWST was used to analyze their surface compositions for the first time. Image credit: Angela Ramirez, UCF

The Mors-Somnus is a member of the same dynamical group as other nearby TNOs and they share spectroscopic characteristics with other cold-classical group objects. This means they probably all formed at about the same time. They probably originated beyond 30 astronomical units from the Sun. Trans-Neptunian binaries such as Mors-Somnus provide a unique way to look at the formation and evolution of planetesimals in that region of space.

Studying the composition of small celestial bodies such as Mors-Somnus gives us precious information about where we came from, Pinilla-Alonso said. “We are studying how the actual chemistry and physics of the TNOs reflect the distribution of molecules based on carbon, oxygen, nitrogen, and hydrogen in the cloud that gave birth to the planets, their moons, and the small bodies,” she says. “These molecules were also the origin of life and water on Earth.”

The Importance of Objects Beyond Neptune

The chemical and physical properties of TNOs offer a treasure trove of information about what conditions were like in the early Solar System. They likely contain pristine materials that existed in the protoplanetary disk from which our Solar System formed, including primitive ices. Those ices don’t change due to solar heating (since the Sun is so far away), but they can be darkened by ultraviolet radiation over time, as planetary scientists have seen at Pluto and other icy worlds. And, those bodies can get transported from their birth regions to other parts of the solar system. If their surfaces don’t change much, then scientists can used spectral studies to trace where groups of objects originated.

The TNO region also contains what scientists call a “dynamical structure”. That is, its distribution of objects by various characteristics, including their orbits and motions over time. Objects and events can change the dynamical structure. For example, the dynamical structure of the trans-Neptunian region bears the traces of planetary migration that occurred in the first billion years of the Solar System’s existence. The TNOs, and in particular, binaries like Mors-Somnus were affected by such migrations.

Migration and Neptune

It’s very likely that this binary pair originally formed well beyond the orbit of Neptune. The researchers found similar spectroscopic characteristics between Mors and Somnus and the cold-classical group. It’s compositional evidence that this binary pair formed well beyond 30 astronomical units (nearly 2.7 billion miles away). Then, they moved to their present positions under the gravitational influence of other planetary migrations.

A model of possible migration paths in the outer solar system due to giant planet migrations. Model: R. Gomes, image by Morbidelli and Levison.

Thanks to gravitational perturbations from Neptune, Mors-Somnus and its neighbors moved closer to the planet. They now orbit in resonance with the planet. All these objects are potential tracers for Neptune’s migration path before it settled into its final orbit, the researchers say.

Binaries separated by distance, as Mors-Somnus is, rarely survive outside of areas bound by gravity, where they are sheltered by other KBOs. To survive migration, they require a slow transportation process toward their destination. The migration of Neptune to its final orbit offered such a leisurely opportunity.

Using JWST to study the surface characteristics of smaller distant worlds is a great accomplishment, according to co-author Pinilla-Alonso. The telescope has studied larger worlds out there, but this is the first time it’s focused on such tiny members of the outer Solar System. “For the first time, we can not only resolve images of systems with multiple components like the Hubble Space Telescope did, but we can also study their composition with a level of detail that only Webb can provide. We can now investigate the formation process of these binaries like never before.”

For More Information

UCF Scientists Use James Webb Space Telescope to Uncover Clues About Neptune’s Evolution
Spectroscopy of the Binary TNO Mors–Somnus with the JWST and Its Relationship to the Cold Classical and Plutino Subpopulations Observed in the DiSCo-TNO Project

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In its first year of operation, the James Webb Space Telescope (JWST) made some profound discoveries. These included providing the sharpest views of iconic cosmic structures (like the Pillars of Creation), transmission spectra from exoplanet atmospheres, and breathtaking views of Jupiter, its largest moons, Saturn’s rings, its largest moon Titan, and Enceladus’ plumes. But Webb also made an unexpected find during its first year of observation that may prove to be a breakthrough: a series of little red dots in a tiny region of the night sky.

These little red dots were observed as part of Webb’s Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) and the First Reionization Epoch Spectroscopically Complete Observations (FRESCO) surveys. According to a new analysis by an international team of astrophysicists, these dots are galactic nuclei containing the precursors of Supermassive Black Holes (SMBHs) that existed during the early Universe. The existence of these black holes shortly after the Big Bang could change our understanding of how the first SMBHs in our Universe formed.

The research was led by Jorryt Matthee, an Assistant Professor in astrophysics at the Institute of Science and Technology Austria (ISTA) and ETH Zürich. He was joined by researchers from the MIT Kavli Institute for Astrophysics and Space Research, the Cosmic Dawn Center (DAWN), the National Astronomical Observatory of Japan (NAOJ), the Niels Bohr Institute, the Max Planck Institute for Astronomy (MPIA), the Centro de Astrobiología (CAB), and multiple universities and observatories. Their findings were published in a study recently published in The Astrophysical Journal.

This image shows the region of the sky in which the record-breaking quasar J0529-4351 was observed by the ESO’s Very Large Telescope (VLT) in Chile. Credit: ESO

Scientists have known for some time that Supermassive Black Holes reside at the center of most massive galaxies. And whereas some are relatively dormant, like the SMBH located in the center of the Milky Way (Sagittarius A*), others are extremely active and are growing at the rate of several Solar masses a year. These fast-growing black holes power particularly luminous Active Galactic Nuclei (AGNs) – or quasars – which become so bright they temporarily outshine all the stars in their disk, the brightest of which are known as quasars.

Quasars are among the brightest objects known to astronomers and can be seen at the very edge of our expanding Universe. In recent years, though, astronomers have spotted several quasars and SMBHs in the early Universe that are larger than cosmological models predict. As Matthee explained in a recent ISTA press release:

“One issue with quasars is that some of them seem to be overly massive, too massive given the age of the Universe at which the quasars are observed. We call them the ‘problematic quasars.’ If we consider that quasars originate from the explosions of massive stars–and that we know their maximum growth rate from the general laws of physics, some of them look like they have grown faster than is possible. It’s like looking at a five-year-old child that is two meters tall. Something doesn’t add up.”

Mathee and his team identified the population of little red dots while studying images taken during the EIGER and FRESCO surveys, a large and medium first-year JWST campaign in which Mathee was involved. The EIGER campaign was specifically designed to search for rare blue supermassive quasars and their environments, and not for quasars in the early Universe. However, Webb‘s Near Infrared Camera (NIRCam) can acquire emissions spectra from all objects in the known Universe. These objects had been previously observed by Hubble and mistaken for regular galaxies.

JWST’s near-infrared view of the star-forming region NGC 604 in the Triangulum galaxy. Credit: NASA, ESA, CSA, STScI

But thanks to the NIRCam’s resolution, the ISTA-led team identified them as SMBHs almost by accident. According to Mathee, this accidental discovery could have profound implications for astronomy and cosmology:

“Without having been developed for this specific purpose, the JWST helped us determine that faint little red dots–found very far away in the Universe’s distant past–are small versions of extremely massive black holes. These special objects could change the way we think about the genesis of black holes. The present findings could bring us one step closer to answering one of the greatest dilemmas in astronomy: According to the current models, some supermassive black holes in the early Universe have simply grown ‘too fast’. Then how did they form?”

The team was able to make the distinction between galaxies and small quasars thanks to NIRCam’s detection of deep-red emission lines (aka. H? spectral lines) that are produced when hydrogen atoms are heated. They also found that the lines they observed had a wide-line profile, which they used to trace the motion of the hot hydrogen gas. “The wider the base of the H? lines, the higher the gas velocity,” said Mathee. “Thus, these spectra tell us that we are looking at a very small gas cloud that moves extremely rapidly and orbits something very massive like an SMBH.”

Just as important were the redshift values they obtained for these SMBGs (Z= 4.2-5.5), which indicate these objects existed more than 12 billion years ago – roughly 1 billion years after the Big Bang. Furthermore, they observed that these SMBHs were not overly massive like those visible in nearby galaxies today. As Mathee indicated:

“While the ‘problematic quasars’ are blue, extremely bright, and reach billions of times the mass of the Sun, the little red dots are more like ‘baby quasars.’ Their masses lie between ten and a hundred million solar masses. Also, they appear red because they are dusty. The dust obscures the black holes and reddens the colors.”

Long exposures made with the Hubble Space Telescope show brilliant quasars flaring in the hearts of six distant galaxies. Credit: NASA/ESA

Eventually, the outflow of hydrogen gas will puncture the clouds of dust and gas that surround and obscure massive black holes (“dust cocoon”), and these smaller SMBHs will evolve into much larger ones. Thus, Mathee and his team hypothesized that the little red dots are small, red versions of giant blue SMBHs in the phase that predates the “problematic quasars.” Through follow-up observations, astronomers can conduct detailed studies of these baby SMBHs, which could lead to a better understanding of how problematic quasars come to exist.

“Black holes and SMBHs are possibly the most interesting things in the Universe. It’s hard to explain why they are there, but they are there,” Mathee concluded. “We hope that this work will help us lift one of the biggest veils of mystery about the Universe.”

Further Reading: ISTA, The Astrophysical Journal

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When stars grow old and die, their mass determines their ultimate fate. Many supermassive stars have futures as neutron stars. But, the question is, how massive can their neutron stars get? That’s one that Professor Fan Yizhong and his team at Purple Mountain Observatory in China set out to answer.

It turns out that a non-rotating neutron star can’t be much more than 2.25 solar masses. If it was more massive, it would face a much more dire fate: to become a black hole. To figure this out, the team at Purple Mountain looked into what’s called the Oppenheimer limit. That’s the critical gravitational mass (abbreviated MTOV) of a massive object. If a neutron star stays below that Oppenheimer limit, it will remain in that state. If it grows more massive, then it collapses into a black hole.

A composite image of the Crab Nebula features X-rays from Chandra (blue and white), optical data from Hubble (purple), and infrared data from Spitzer (pink). The Crab Nebula is powered by a quickly spinning, highly magnetized neutron star called a pulsar, which was formed when a massive star ran out of its nuclear fuel and collapsed. Scientists now want to know how much mass characterizes a neutron star as opposed to a black hole. Understanding the Physics of a Neutron Star

So, why determine the upper mass of a neutron star? The Oppenheimer limit for these objects has some implications for both astrophysics and nuclear physics. Essentially, it indicates that compact objects with masses greater than 2.25 solar masses are probably what scientists term the “lightest” black holes. Those objects would likely exist in a range of 2.5 to 3 solar masses.

The whole thing is rooted in the way that stars age. Everything depends on their starting mass. So, for example, our Sun is a lower-mass yellow dwarf and it will take more than 10 billion years to go through its whole life cycle. It’s about 4.5 billion years old now. As it ages, it will consume heavier elements in its core, which will heat it up. That drives expansion, which means the Sun will become a red giant and cast off its outer layers beginning in about five billion years. Eventually, it will shrink to become a white dwarf. That tiny object will contain less than the mass of the Sun, although some white dwarfs can be slightly more massive.

How a Neutron Star Forms

Stars much more massive than the Sun go through the same cycle, but they end their lives in supernova explosions. What’s left becomes a black hole. Or, if there’s not quite enough mass left after the explosion, the remnant becomes a neutron star. So, that means there’s a delicate line between it and a black hole. That line is the Oppenheimer limit.

X-ray image of the Tycho supernova, also known as SN 1572, located between 8,000 and 9,800 light-years from Earth. Its core collapse could result in a neutron star or a black hole, depending on final mass. (Credit: X-ray: NASA/CXC/RIKEN & GSFC/T. Sato et al; Optical: DSS)

Stars between 8 and 25 solar masses produce neutron stars. Something called “neutron degeneracy pressure” holds those odd remnants together. The leftover core of the star compresses after the supernova explosion. But, neutrons and protons in atomic nuclei in the core get pushed tightly together and they can’t be compressed any more. So, the system goes into a weird equilibrium. At that point, the resulting neutron star is approaching the Oppenheimer limit. If the object gains (or has) any more mass, that puts it over the limit. The result is a black hole.

Refining the Oppenheimer Limit for Neutron Stars

Professor Fan’s team worked to find a more precise value for the Oppenheimer Limit. To do this, they gathered data from such observations as those made by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the VIRGO gravitational wave detector, as well as an instrument aboard the International Space Station called The Neutron Star Interior Composition Explorer Mission (NICER). These and other missions detect the effects of neutron star collisions and neutron star-black hole encounters. NICER, in particular, studies the timing of x-ray emissions at neutron stars and works to answer the question: How big is a neutron star? By knowing the size and mass of neutron stars, astronomers can gain a further understanding of their formation and the exotic matter they contain.

The team incorporated information about the maximum mass cutoff (i.e. what’s the highest level of mass a neutron star can have) inferred from the distribution of these objects. They used models of the equation of state in their work. The equation of state basically looks at the state of matter in the neutron star (and black hole) and the models describe the parameters under which it exists (including pressure, volume, and temperature). The result of their work gives not only an upper bound to the mass of the neutron star (~2.5 solar masses) but also reveals that such a neutron star would have a radius of around 11.9 kilometers.

It’s interesting to see the precision in these measurements and models, based on actual data from multi-messenger observations of gravitational waves and soft X-ray emissions. Fan and the team suggest in the paper they published about their work that the objects with masses between 2.5 and 3 solar masses (detected by second-generation gravitational wave detectors) are most likely the lightest black holes.

Further Implications

The work also has some pretty interesting implications for cosmology, in particular the Hubble Constant. That’s the value assigned to the rate at which the Universe is expanding. It lies somewhere around 70 kilometers per second per megaparsec (plus or minus 2.2 km/sec/Mpc). The numbers depend on which methods astronomers use to calculate them.

The Fan team’s work suggests that the mass cutoff for neutron stars detected by gravitational waves should align with MTOV. That does not change with redshift. The Oppenheimer Limit mass cutoff is associated with both the redshifted mass of the object and its redshift. That’s predicted by the cosmological model and luminosity distance. This provides a new method to test the underlying cosmological model of the Universe. The current model begins with the Big Bang, inflation, and expansion. It also includes the distribution of all the matter (including dark and baryonic matter), and in corporates the contribution of dark energy.

For More Information

Maximum mass of non-rotating neutron star precisely inferred to be 2.25 solar masses
Maximum gravitational mass MTOV = 2.25 +0.08/-0.07 Ms inferred at about 3% precision with multimessenger data of neutron stars
ArXiv Preprint

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