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It is now generally accepted that 66 million years ago a large asteroid smacked into the Earth, causing the large Chicxulub crater off the coast of Mexico. This was a catastrophic event, affecting the entire globe. Fire rained down causing forest fires across much of the globe, while ash and debris blocked out the sun. A tsunami washed over North America – one site in North Dakota contains fossils from the day the asteroid hit, including fish with embedded asteroid debris. About 75% of species went extinct as a result, including all non-avian dinosaurs.

For a time there has been an alternate theory that intense vulcanism at the Deccan Traps near modern-day India is what did-in the dinosaurs, or at least set them up for the final coup de grace of the asteroid. I think the evidence strongly favors the asteroid hypothesis, and this is the way scientific opinion has been moving. Although the debate is by no means over, a majority of scientists now accept the asteroid hypothesis.

But there is also a wrinkle to the impact theory – perhaps there was more than one asteroid impact. I wrote in 2010 about this question, mentioning several other candidate craters that seem to date to around the same time. Now we have a new candidate for a second KT impact – the Nadir crater off the coast of West Africa.

Geologists first published about the Nadir crater in 2022, discussing it as a candidate crater. They wrote at the time:

“Our stratigraphic framework suggests that the crater formed at or near the Cretaceous-Paleogene boundary (~66 million years ago), approximately the same age as the Chicxulub impact crater. We hypothesize that this formed as part of a closely timed impact cluster or by breakup of a common parent asteroid.”

Now they have published a follow up study, having been given access to private seismic data that allows for a detailed 3D analysis of the crater site. This is important because of how scientists identify impact craters. The gold standard is to identify physical evidence of impact, such as shock crystals. There are telltale minerals that can only be formed by the intense sudden power of an impact, or that form when debris is thrown into the high atmosphere while molten and then rains back down. These are conclusive signs of an impact. But there are many somewhat circular structures in the world, and often they may be prematurely declared a crater without solid evidence. So geologists are cautious and skeptical.

For the Nadir crater, which is on the sea floor, we do not have physical evidence. The initial study showed that it has a candidate circular structure, but this was not enough evidence to convince the scientific community. The detailed new analysis, however, is more compelling. First the scientists find that it does have a complete circular structure consistent with an impact basin. Even more significant, however, is that they have documented a “central uplift”, which is a characteristic sign of an impact crater. When asteroids hit they cause a depression and liquify the underlying rock. This causes a shockwave which rebounds, causing the molten rock to uplift in the center of the crater, leaving behind an uplift. This means that a circular basin with an uplift in the exact middle is a signature of an impact. This is solid and convincing evidence, even without the physical evidence of impact crystals. They write:

“Our new study published in Communications Earth & Environment 3 presents this new, state-of-the-art 3D data, revealing the architecture of the crater in exceptional detail and confirms (beyond reasonable doubt!) an impact origin for the crater. This is the first time that an impact structure has ever been imaged fully with high-resolution seismic data like this and it is a real treasure trove of information to help us to reconstruct how this crater formed and evolved.”

Sounds pretty convincing. But this leaves the questions they raised in their study two years ago – did this asteroid hit at the exact same time as the Chicxulub asteroid? If not, how far apart were they? If they did hit at the same time, were they originally part of the same asteroid? Given that there are other candidate craters that date to the same period of time, perhaps the asteroid broke up into multiple pieces that all struck the Earth at the same time.

If these asteroids were not originally part of the same asteroid, then what are the other possibilities? It is possible, although statistically unlikely, that there were simply different independent major impacts within a short time of each other. There is nothing to keep this from happening, and given the history of life on Earth perhaps it’s not that surprising, but it would be a statistical fluke.

The other possibility is that, even if they were different asteroids, perhaps there was some astronomical event that caused multiple chunks of rock and ice to swarm into the inner solar system. This would have caused a temporary period of relatively high bombardment. Perhaps a rogue planet swung by our solar system, scattering material from the Kuiper belt, some of which found its way to Earth.

The authors propose to drill into this structure, to get that physical evidence that would be so helpful. Not only would this confirm its impact status, but we may be able to tell if the chunk of rock that caused the Nadir crater has the same mineral signature as the Chicxulub asteroid. I suspect we could also tell their relative timing. Perhaps we could see the iridium layer from the Chicxulub impact, and see how that relates to the Nadir impact.

We may be able to answer – were the dinosaurs just really unlucky, or was the Chicxulub impact event more devastating than we even realized? Either way I look forward to more scientific investigation of the Nadir crater.

The post Nadir Crater – A Double Tap for Dinosaurs? first appeared on NeuroLogica Blog.

Since the 1970s, astronomers have observed that supermassive black holes (SMBHs) reside at the centers of most massive galaxies. In some cases, these black holes accelerate gas and dust from their poles, forming relativistic jets that can extend for thousands of light-years. Using the NASA/ESA Hubble Space Telescope, a team of astronomers observed the jet emanating from the center of M87, the supermassive galaxy located 53.5 million light-years away. To their surprise, the team observed nova erupting along the jet’s trajectory, twice as many as they observed in M87 itself.

The team was led by Alec M. Lessing, a Stanford University astronomer, and included researchers from the American Museum of Natural History, the University of Maryland Baltimore, Columbia University, Yale University, the SETI Institute, and NASA’s Goddard Space Flight Center. The paper detailing their findings recently appeared in The Astrophysical Journal. Their research was part of a 9-month survey of the M87 galaxy using Hubble’s near-UV Cosmic Origins Spectrograph (COS).

To date, all novae have been observed in double-star systems consisting of a red giant star and a white dwarf companion. In these systems, the outer layers of the red giant are siphoned away by the white dwarf and accreted onto its surface. When the white dwarf has accumulated enough hydrogen, the layer explodes in a “nova eruption,” and the cycle begins again. When the team observed M87 using Hubble’s COS, they found twice as many novae eruptions near the 3000-light-year-long jet than in the galaxy itself during the surveyed period.

A Hubble image of M87 shows a 3,000-light-year-long jet of plasma blasting from the galaxy’s 6.5-billion-solar-mass central black hole. Credit: NASA/ESA/STScI/A. Lessing et al. (2004).

These findings imply that there are twice as many nova-forming double-star systems near the jet or that these systems erupt twice as often as similar systems elsewhere in the galaxy. Another possibility is that the jet is heating the red giant stars in these binary systems, causing them to overflow further and dump more hydrogen onto the dwarf companion. However, the researchers determined that this heating is not significant enough to have this effect. As Lessing explained in an ESA press release:

“We don’t know what’s going on, but it’s just a very exciting finding. This means there’s something missing from our understanding of how black hole jets interact with their surroundings… There’s something that the jet is doing to the star systems that wander into the surrounding neighborhood.

“Maybe the jet somehow snowplows hydrogen fuel onto the white dwarfs, causing them to erupt more frequently. But it’s not clear that it’s a physical pushing. It could be the effect of the pressure of the light emanating from the jet. When you deliver hydrogen faster, you get eruptions faster. Something might be doubling the mass transfer rate onto the white dwarfs near the jet.”

This is not the first time astronomers have noticed increased levels of activity around the M87 jet. Shortly after Hubble launched in 1990, astronomers observed the galaxy’s SMBH using its first-generation Faint Object Camera (FOC). These observations revealed “transient events” that could be evidence of novae, but the FOC’s view was too narrow to compare what was happening between the jet and in the near-jet region. Thanks to the nine-month campaign that relied on Hubble’s upgraded cameras (which have a wider view) and viewed the jet’s environment every five days, the team was able to count the novae along the jet’s trajectory.

Sag A* compared to M87* and the orbit of Mercury. Credit: EHT collaboration

The observations, which were the deepest images of M87 ever taken, revealed 94 novae within the M87 galaxy’s inner region. Said co-author Michael Shara, the Curator of Astrophysics at the American Museum of Natural History:

“The jet was not the only thing that we were looking at — we were looking at the entire inner galaxy. Once you plotted all known novae on top of M87 you didn’t need statistics to convince yourself that there is an excess of novae along the jet. This is not rocket science. We made the discovery simply by looking at the images. And while we were really surprised, our statistical analyses of the data confirmed what we clearly saw.”

These observations confirm that the venerable Hubble still has the capability to reveal new and interesting things about the Universe. In addition, these findings provide an opportunity for follow-up studies to learn more about how relativistic jets could influence star systems extending well beyond their galaxies.

Further Reading: ESA Hubble, The Astrophysical Journal

The post Jets From Supermassive Black Holes Create New Stars Along Their Trajectory appeared first on Universe Today.

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deepSPACE isn't a futuristic film, a new videogame or the next season of a classic TV series. In fact, the new design software developed by an aerospace engineer isn't about outer space at all. This new tool takes your concept and requirements and rapidly generates design configurations from conventional to out-of-this-world, including a 3D CAD model and performance evaluations.

deepSPACE isn't a futuristic film, a new videogame or the next season of a classic TV series. In fact, the new design software developed by an aerospace engineer isn't about outer space at all. This new tool takes your concept and requirements and rapidly generates design configurations from conventional to out-of-this-world, including a 3D CAD model and performance evaluations.

The two Voyager spacecraft have been speeding through space since 1977, powered by decaying chunks of plutonium that produce less and less energy every year. With less electricity available, NASA has decided to shut down one experiment on Voyager 2, the plasma science instrument. This device measures the quantity and direction of ionized particles passing the spacecraft. While Voyager 2 still has enough electricity to support its four other operational instruments, it will likely be down to just one by the 2030s.

NASA said that over the past several years, engineers for the mission have taken steps to avoid turning off any science instruments for as long as possible since the science data collected by the two Voyager probes is unique. As the first spacecraft to reach interstellar space — the region outside the heliosphere – this is currently our only chance to study this region. However, this particular instrument has been collecting limited data in recent years due to its orientation relative to the direction that plasma is flowing in interstellar space.

The 47-year old Voyager 2 is traveling at about 15 km/second (35,000 miles per hour) and is currently more than 20.5 billion km (12.8 billion miles) from Earth. The four remaining science instruments are studying the region outside our heliosphere and include a magnetometer to study the interplanetary magnetic field, a charged particle instrument that measures the distributions of ions and electrons, a cosmic ray system that determines the origin of interstellar cosmic rays, and a plasma wave detector.

The Grand Tour The Grand Tour ‘poster.’ Image: NASA/JPL

The two Voyagers both launched in 1977 (August and September), and their different trajectories were designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and the 1980s which allowed for a four-planet tour for a minimum of propellant and trip time. The positions of those planets — which only occurs about every 175 years — took Voyager 2 (which launched first) past the gas giants Jupiter and Saturn, and then its flight path allowed for encounters with the ice giants Uranus and Neptune. It remains the only spacecraft to have visited either of the ice giant planets.

Voyager 1 made flybys of Jupiter, Saturn, and Saturn’s largest moon, Titan. Both spacecraft made incredible discoveries at the distant planets, and the astounding imagery sent back to Earth opened a whole new way of looking at the outer Solar System.

Europa seen during Voyager 2 Closest Approach. Credit: NASA/JPL

Now, they’re in the Voyager Interstellar Mission phase, where their data helped characterize and study the regions and boundaries of the outer heliosphere, and now explores the interstellar medium. Voyager 1 crossed the heliopause and entered interstellar space on August 25, 2012. Voyager 2 entered interstellar space on November 5, 2018, at a distance of 119.7 AU. Both communicate with Earth via the Deep Space Network. It takes nearly a day for one-way communications to reach each spacecraft and another day for data to be sent back to Earth.

Dwindling Power Pellet of Pu-238. RTGs are constructed using marshmallow-sized pellets of Pu-238. As it decays, interactions between the alpha particles and the shielding material produce heat that can be converted into electricity.

Each Voyager 2 is powered by three multihundred-watt radioisotope thermoelectric generators (RTG). At launch, each RTG provided enough heat to generate approximately 157 watts of electrical power, and so collectively, the RTGs supplied the spacecraft with 470 watts at launch, and their power halves every 87.7 years. They were predicted to allow operations to continue until at least 2020, but are still providing enough energy for some data collection and communications. NASA estimates they lose about 4 watts of power each year.

After the twin Voyagers completed their exploration of the giant planets in the 1980s, the mission team turned off several science instruments that would not be used to study of interstellar space. That gave the spacecraft plenty of extra power until a few years ago. Since then, the team has turned off all onboard systems not essential for keeping the probes working, including some heaters. In order to postpone having to shut off another science instrument, they also adjusted how Voyager 2’s voltage is monitored.

The device that was recently turned off, the plasma science instrument, measured the amount of plasma (electrically charged atoms) and the direction it is flowing. In 2018, the plasma science instrument helped determine that Voyager 2 left the heliosphere. Inside the heliosphere, particles from the Sun flow outward, away from our parent star. Since the heliosphere is moving through interstellar space, the plasma flows in almost the opposite direction of the solar particles.

NASA’s Voyager 2 Probe Enters Interstellar Space This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto. Voyager 1 exited the heliosphere in August 2012. Voyager 2 exited at a different location in November 2018. Credit: NASA/JPL-Caltech

When Voyager 2 exited the heliosphere, the flow of plasma into the instrument dropped off dramatically. Most recently, the instrument has been used only once every three months, when the spacecraft does a 360-degree turn on the axis pointed toward the Sun. This limited usage factored into the mission’s decision to turn this instrument off before others.

NASA said the same plasma science instrument on Voyager 1 stopped working in 1980 and was turned off in 2007 to save power.

The post NASA Turns Off One of Voyager 2's Science Instruments appeared first on Universe Today.

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