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Novel propulsion systems are one of the most important ways to push space exploration forward – literally. Traditional propulsion systems, like chemical rockets, are good at getting spacecraft out of gravity wells but not so great at traveling in free space. More modern systems, like electric propulsion, are better at providing long-term propulsion but are very slow. Others haven’t even made it to space, like nuclear thermal rockets. But there’s one type that could trump them all – fusion propulsion. It has the benefit of significant thrust and excellent fuel efficiency and could open up the whole solar system in ways other systems could only dream of. One company, Helicity Space, thinks they are on the path to developing a working version of just such a fusion propulsion system, and they just received a NASA Institute of Advanced Concepts (NIAC) grant to continue its development.

The NIAC grant itself focuses on exploring the heliosphere—an area surrounding the Sun (including on top of it) that our star influences. It is huge in terms of the amount of space covered and not well understood because, typically, missions only stay in the plane of the ecliptic, and if they go far enough to reach the outer stretches of the heliosphere, it is only after decades of travel, like the Voyager space probes.

Helicity proposes using fusion rockets to send a constellation of spacecraft to all parts of the heliosphere with sensors to detect things such as plasma properties, the amount of energetic particles, and the amount of dust in a given region. This constellation could provide heliophysics with a much more complete picture of what the heliosphere looks like.

The idea of fusion rockets have been around for a long time, as Fraser discusses.

However, the real innovation the NIAC grant focuses on isn’t sensor instrumentation but the propulsion system. Fusion propulsion has been a dream of many space exploration enthusiasts for decades. Still, it has seemed to suffer from the same fate of technical development hell that its ground-based cousins, the large-scale power-positive fusion plants, have. The physics of plasma constraint and forced fusion are challenging, to say the least, so projects like the International Thermonuclear Experimental Reactor (ITER) cost billions of dollars and take decades to complete.

Helicity, on the other hand, is a scrappy start-up based in Pasadena, and they believe they can produce a functioning fusion engine well before ITER hits its full power in 2035. In an interview with Fraser, Setthivoine You, the company’s co-founder and chief technologist, explains that if you’re trying to make money from a fusion power plant, “you need to do net gains of 20, 30, 40, 50 [times] more fusion energy out than what you put in [and] you have to do it every single second, 24 hours a day, 365 days a year.”

On the other hand, Helicity’s engine doesn’t have to operate constantly and can produce net gains of only 10x, and only occasionally. In such an operational mode, the engineering challenge becomes much more tractable. The company has already built a prototype unit at its facility in Pasadena and has been presenting at several conferences and publishing academic papers detailing its progress all along.

Isaac Arthur covers the details of fusion propulsion systems.
Credit – Isaac Arthur YouTube Channel

The NIAC grant will allow them to start fleshing out the technical details of what the engine would require to complete the heliosphere mission, allowing them to tweak the engine to get to those performance metrics. But that’s not the only mission this system can be used for. Getting to Mars in about a month and a half, rather than the nine months using traditional propulsion, has been one of the space exploration community’s main selling points to such a system.

During the interview, Fraser mentioned even more outlandish missions, like one to the solar gravitational lens point, where we could use the Sun’s gravitational lensing effect to image exoplanets around other stars directly. Dr. You mentioned, “Our proposal could take us out there in less than 10 years”, dramatically shorter than any currently proposed propulsion system. Unlike alternatives like giant solar sails, it would also have the added benefit of slowing down and holding its position.

In addition to the advanced propulsion system, though, Helicity mentions developing additional technologies that could directly benefit people back on the ground as part of their proposal. Dr. You mentions “high-high solid-state switches, energy storage, systems, [and] magnetic coils” as potentially useful tools that would result from the development of the engine.

Where fusion rockets lie compared to other forms of propulsion in terms of power and efficiency.
Credit – Helicity Space

Much of the challenges facing the development team appear to focus on developing these “subsystems inside plasma sources,” which is one particular challenge Dr. You calls out, along with several other engineering challenges. Basically, proving the engine will work in space is the biggest technical hurdle at this point – and the Phase I NIAC grant is another step towards doing so.

It is not the first step, however—Helicity is backed by several VC firms and large aerospace companies, including Airbus and Lockheed Martin. The fact that they already have an experimental system up and running also lends credence to their ability to execute the mission of bringing fusion power to space. If they manage to do so, a long-held dream of space exploration enthusiasts will be realized, and the whole solar system will be opened up for human use.

Learn More:
NASA / Helicity Space – Fusion-Enabled Comprehensive Exploration of the Heliosphere
Helicity Space – Technology
UT – Magnetic Fusion Plasma Engines Could Carry us Across the Solar System and Into Interstellar Space
UT – Impatient? A Spacecraft Could Get to Titan in Only 2 Years Using a Direct Fusion Drive

Lead Image:
Image of the heliosphere and an artist’s concept of the fusion drive ship that could be sent to monitor it.
Credit – NASA / Helicity Space

The post Fusion-Enabled Comprehensive Exploration of the Heliosphere appeared first on Universe Today.

Last week, when I wasn’t watching democracy bleed, I was participating in an international virtual workshop, attended by experts from many countries. This meeting of particle experimenters and particle theorists focused on the hypothetical possibility known as “hidden valleys” or “dark sectors”. (As shorthand I’ll refer to them as “HV/DS”). The idea of an HV/DS is that the known elementary particles and forces, which collectively form the Standard Model of particle physics, might be supplemented by additional undiscovered particles that don’t interact with the known forces (other than gravity), but have forces of their own. All sorts of interesting and subtle phenomena, such as this one or this one or this one, might arise if an HV/DS exists in nature.

Of course, according to certain self-appointed guardians of truth, the Standard Model is clearly all there is to be found at the Large Hadron Collider [LHC], all activities at CERN are now just a waste of money, and there’s no point in reading this blog post. Well, I freely admit that it is possible that these individuals have a direct line to God, and are privy to cosmic knowledge that I don’t have. But as far as I know, physics is still an experimental science; our world may be going backwards in many other ways, but I don’t think we should return to Medieval modes of thought, where the opinion of a theorist such as Aristotle was often far more important than actually checking whether that opinion was correct.

According to the methods of modern science, the views of any particular scientist, no matter how vocal, have little value. It doesn’t matter how smart they are; even Nobel Prize-winning theorists have often been wrong. For instance, Murray Gell-Mann said for years that quarks were just a mathematical organizing principle, not actual particles; Martinus Veltman insisted there would be no Higgs boson; Frank Wilczek was confident that supersymmetry would be found at the LHC; and we needn’t rehash all the things that Newton and Einstein were wrong about. In general, theorists who make confident proclamations about nature have a terrible track record, and only get it right very rarely.

The central question for modern science is not about theorists at all. It is this: “What do we know from experiments?”

And when it comes to the possibility of an HV/DS, the answer is “not much… not yet anyway.”

The good news is that we do not need to build another multibillion dollar experimental facility to search for this kind of physics. The existing LHC will do just fine for now; all we need to do is take full advantage of its data. But experimenters and theorists working together must develop the right strategies to search for the relevant clues in the LHC’s vast data sets. That requires completely understanding how an HV/DS might manifest itself, a matter which is far from simple.

Last week’s workshop covered many topics related to these issues. Today I’ll just discuss one: an example of a powerful, novel search strategy used by the ATLAS experiment. (It’s over a year old, but it appeared as my book was coming out, and I was too busy to cover it then.) I’ll explain why it is a good way to look for strong forces in a hidden valley/dark sector, and why it covers ground that, in the long history of particle physics, has never previously been explored.

Jets-of-Jets, and Why They’re Tricky

I already discussed topics relevant to today’s post in this one from 2022, where I wrote about a similar workshop, and you may well find reading that post useful as a complement to this one. There the focus was on something called “semi-visible jets”, and in the process of describing them I also wrote about similar “jets-of-jets”, which are today’s topic. So here is the second figure from that older post, showing ordinary jets from known particles, which are covered in this post, as well as the jets-of-jets and semi-visible jets that might arise from what is known as a “confining HV/DS.”

Figure 1: Left: Ordinary jets of hadrons will form from an ordinary, fast-moving quark; the total energy of the jet is approximately the total energy of the unobserved original quark. Center: A fast-moving hidden quark will make a jet of hidden (or “dark”) hadrons; but these, in turn, may all decay to ordinary quark/anti-quark pairs, each of which leads to a jet of ordinary hadrons. The result is a jet of jets. Right: if only some of the dark hadrons decay, while some do not, then the jet of jets is semi-visible; those that don’t decay (grey dotted arrows) will escape the detector unobserved, while the rest will produce observable particles.

How does a jet-of-jets form? In a hidden valley with a “confining” force (a few examples of which were explored by Kathryn Zurek and myself in our first paper on this subject), some or all of the HV/DS particles are subject to a force that resembles one we are familiar with: the strong nuclear force that binds the known quarks and gluons into protons, neutrons, pions, and other hadrons. By analogy, a confining HV/DS may have “valley quarks” and “valley gluons” (also referred to as “dark quarks” and “dark gluons”) which are bound by their own strong force into dark hadrons.

The analogy often goes further. As shown at the left of Fig. 1, when a high-energy quark or gluon comes flying out of a collision of protons in the LHC, it manifests itself as a spray of hadrons, known as a jet. I’ll call this an “ordinary jet.” Most of the particles in that ordinary jet are ordinary pions, with a few other familiar particles, and they are observed by the LHC detectors. Images of these jets (not photographs, but precise reconstructions of what was observed in the detector) tend to look something like what is shown in Fig. 2. In this picture, the tracks from each jet have been given a particular color. You see that there are quite a lot of tracks in the highest-energy jets, whose tracks are colored green and red. [These tracks are mostly from the electrically charged pions. Electrically neutral pions turn immediately into photons, which are also detected but don’t leave tracks; they and instead are absorbed in the detector’s “calorimeters” (the red and green circular regions.) The energy from all the particles, with and without tracks, is depicted by the dark-green/yellow/dark-red bars drawn onto the calorimeters.]

Figure 2: From ATLAS, a typical proton-proton collision with two energetic ordinary jets (plus a few less energetic ones.) The proton beams are coming in and out of the screen; the collision point is at dead center. From the collision emerge two energetic jets, the narrow groupings of nearly straight tracks shown in bright green and red; these (and other particles that don’t make tracks) leave lots of energy in the “calorimeters”, as shown by the dark green/yellow and dark red rectangles at the outer edges of the detector.

But what happens if a dark quark or dark gluon is produced in that collision? Well, as shown in the center panel of Fig. 1, a spray of dark hadrons results, in the form of a dark jet. The dark hadrons may be of various types; their precise nature depends on the details of the HV/DS. But one thing is certain: because they are hidden (dark), they can’t be affected by any of the Standard Model’s forces: electromagnetic, strong nuclear, or weak nuclear. As a result, dark hadrons interact with an LHC detector even less than neutrinos do, which means they sail right through it. And so there’s no hope of observing these objects unless they transform into something else that we can observe.

Fortunately [in fact this was the main point of my 2006 paper with Zurek], in many HV/DS examples, some or all of the dark particles

• will in fact decay to known, observable particles, and
• will do so fast enough that they can be observed in an LHC detector.

This is what makes the whole subject experimentally interesting.

For today, the main question is whether all or some of the dark hadrons decay faster than a trillionth of a second. If all of them do, then, as depicted in the central panel of Fig. 1, the dark jet of dark hadrons may turn into a jet-of-jets (or into something similar-looking, if a bit more complex to describe.) If only a fraction of the dark hadrons decay, while others pass unobserved through the detector, then the result is a semi-visible jet (or semi-visible jet-of-jets, really), shown in the right panel of Fig. 1.

Cool! Let’s go look through LHC data for jets-of-jets!

The Key Distinction Between Jets and Jets-Of-Jets

Not so fast. There’s a problem.

You see, ordinary jets come in such enormous numbers, and vary so greatly, that it’s not immediately obvious how to distinguish a somewhat unusual ordinary jet from a true jet-of-jets. How can this be done?

Theorists and especially experimenters have been looking into all sorts of complex approaches. Intricate measures of jet-weirdness invented by various physicists are being pumped en masse into machine learning algorithms (the sort of AI that particle physicists have been doing for over a decade). I’m all in favor of sophisticated strategies — go for it!

However, as I’ve emphasized again and again in these workshops, sometimes it’s worth doing the easy thing first. And in this context, the ATLAS experimental collaboration did just that. They used the simplest strategy you can think of — the one already suggested by the left and center panels of Figure 1. They exploit the fact that a jet-of-jets of energy E (or transverse momentum pT) generally has more tracks than an ordinary jet with the same energy E (or pT). [This fact, emphasized in Figs. 19 and 20 of this paper from 2008, follows from properties of confining forces; I’ll explain its origin in my next post on this subject.]

So at first glance, to look for this sign of an HV/DS, all one has to do is look for jets with an unusual number of tracks. Easy!

Well, no. Nothing’s ever quite that simple at the LHC. What complicates the search is that the number of LHC collisions with jets-of-jets might be just a handful — maybe two hundred? forty? a dozen? Making HV/DS particles is a very rare process. The number of LHC collisions with ordinary jets is gigantic by comparison! Collisions that make pairs of ordinary jets with energy above 1 TeV — a significant fraction of the energy of LHC’s proton-proton collisions — number in the many thousands. So this is a needles-in-a-haystack problem, where each of the needles, rather than being shiny metal, looks a lot like an unusual stalk of hay.

For example, look at the event in Fig. 3 (also from ATLAS). There are two spectacular jets, rather wide, with lots of tracks (and lots of energy, as indicated by the yellow rectangles on the detector’s outer regions.) Might this show two jets-of-jets?

Figure 3: As in Fig. 2, but showing an event with two jets that each display an extreme numbers of tracks. This is what a pair of jets-of-jets from an HV/DS might look like. But is that what it is?

Maybe. Or maybe not; more likely this collision produced two really unusual but ordinary jets. How are we to tell the difference?

In fact, we can’t easily tell, not without sophisticated methods. But with a simple strategy, we can tell statistically if the jets-of-jets are there, employing a trick of a sort commonly used at the LHC.

A Efficient, Simple, Broad Experimental Strategy

The key: both the ordinary jets and the jets-of-jets often come in pairs — for analogous reasons. It’s common for a high-energy quark to be made with a high-energy anti-quark going the opposite direction, giving two ordinary jets; and similarly it would be common for a dark quark to be made with a dark anti-quark, making two jets-of-jets. (Gluon pairs are also common, as would be pairs of dark gluons.)

This suggests the following simple strategy:

• Gather all collisions that exhibit two energetic jets (we’ll call them “dijet events”) and that satisfy a certain criterion that I’ll explain in the next section.
• Count the tracks in each jet; let’s call the number of tracks in the two jets n1 and n2.
• Suppose that we consider 75 tracks or more to be unusual — more typical of a jet-of-jets than of an ordinary jet. Then we can separate the events into four classes:
  • Class A: Those events where n1 and n2 are both less than 75;
  • Class B: Those events where n1 < 75 ≤ n2 ;
  • Class C: Those events where n2 < 75 ≤ n1 ;
  • Class D: Those events where n1 and n2 are both 75 or greater.
• Importantly, the two ordinary jets in a typical dijet event form largely independent of one another (with some caveats that we’ll ignore), so we can apply simple probability. If the probability that an ordinary jet has 75 tracks or more is p, then (see Fig. 4 below)
  • the number of events NA in class A is proportional to (1-p)2,
  • the number of events NB in class B and NC in class C are both proportional to p(1-p), and
  • the number of events ND in class D is proportional to p2.

These proportions are just those of the areas of the corresponding regions of the divided square in Fig. 4.

Figure 4: For independently-forming jets that have probability p of being unusual, the relations between NA , NB , NC and ND are exactly those of the areas of a square cut into four pieces, where each side of the square is split into lengths p and 1-p. Knowing the area of regions A and B (or C), one can predict the area of D. The same logic allows prediction of ND from NA , NB , NC.

As suggested by Fig. 4, because the two jets are of the same type, NB ≈ NC (where “≈“ means “approximately equal” — they differ only due to random fluctuations.) Furthermore, because the probability p of having more than 75 tracks in an ordinary jet is really small, we can write a few relations that are approximately true both of the numbers in each class and of the corresponding areas of the square in Fig. 4.

• Ntotal ≈ NA
  • (i.e. almost all the events are in Class A)
• NB / NA ≈ NC / NA ≈ p(1-p) / (1-p)2 = p / (1+p) ≈ p
  • (i.e. the fraction of events in class B or C is nearly p)
• ND / Ntotal ≈ p2 ≈ (NB / NA)2 ≈ NB NC / ( Ntotal )2
  • (i.e therefore by measuring NB , NC , and Ntotal , we can predict the number of events in class D. )

Would you believe this strategy and others like it are actually called the “ABCD method” by experimental particle physicists? That name is more than a little embarrassing. But the method is indeed simple, and whatever we call it, it works. Specifically, it allows us to predict the number ND before we actually count the number of events in class D. And when the count is made, two things may happen:

• If the measured ND is roughly the same as the prediction, we know that most of the events in Class D — the dijet events where both jets have an extreme number of tracks — are probably pairs of unusual ordinary jets, and there’s no sign of anything unexpected.
• If the measured ND is significantly larger than the prediction, then we have discovered a new source of dijet events where both jets have an extreme number of tracks, one that is not expected in the Standard Model. Maybe they are from an HV/DS, or maybe from something else — but that’s a detail to be figured out later, when we’re done drinking all the champagne in France.

[Note: I chose the number 75 for simplicity. The experimenters make their choice in a more complicated way, but this is a detail which doesn’t change the basic logic of the search.]

No similar search for jets-of-jets had ever previously been performed, so I’m sure the experimenters were quite excited when they finally unblinded their results and took a look at the data. But nothing unusual was seen. (If it had been, you would have already heard about it in the press, and France would have run out of bubbly.) Still, even though a null result isn’t nearly as revolutionarily important as a discovery, it is still evolutionarily important, representing an important increase in our knowledge.

What exactly we learn from this null result depends on the individual HV/DS example. Basically, if a specific HV/DS produces a lot of jets-of-jets, and those jets-of-jets have lots of tracks, then it would have been observed, so we can now forget about it. HV/DS models that produce fewer or less active jets-of-jets are still viable. What’s nice about this search is that its elegant simplicity allows a theorist like me to quickly check whether any particular HV/DS is now excluded by this data. That task won’t be so easy for the more sophisticated approaches that are being considered for other search strategies, even though they will be even more powerful, and necessary for some purposes.

One More Criterion in the Strategy

As I began to outline the strategy, I mentioned a criterion that was added when the dijet events were initially selected. Here’s what it is.

Click here for the details

The ATLAS experimenters assumed a simple and common scenario. They imagined that the jets-of-jets are produced when a new particle X with a high mass mX is produced, and then the X immediately decays to two jets-of-jets. Simple examples of what X might be are

• a heavy version of a Z boson made in a collision of a quark and an anti-quark, or
• a heavy version of a Higgs-like boson created in the collision of two gluons.

An example of the former, in which the heavy Z-like particle is called a “Z-prime”, is shown in Fig. 5.

Figure 5: A diagram showing a possible source of HV/DS jets-of-jets events, in which a quark and anti-quark (left) collide, making a Z-like boson of high mass, which subsequently decays (right) to a dark quark and anti-quark.

If the X particle were stationary, then its total energy would be given by Einstein’s formula E=mXc2. If such a particle were subsequently to decay into two jets-of-jets, then the total energy of the two jet-of-jets would then also be E=mXc2 (by energy conservation.) In such a situation, all the events from X particles would have the same total energy, and we could use that to separate possible jets-of-jets events from pairs of ordinary jets, whose energy would be far more random.

Typically, however, the X particle made in a proton-proton collision will not be stationary. Fortunately, a similar strategy can be applied, using something know as the invariant mass of the two jets-of-jets, which will always be mX. [Well, nothing is simple at the LHC; these statements are approximately true, for various reasons we needn’t get into now.]

And so, when carrying out the strategy, the experimenters

• Pick a possible value of mX ;
• Select all dijet events where the two jets together are measured to have an invariant mass approximately equal to mX ;
• Carry out an ABCD search only within that selected set of events, to see if the number of Class D events exceeds the prediction;
• Repeat for a new value of mX .

Missed Opportunity?

I have only one critique of this search, one of omission. It’s rather unfair, since we must give the experimenters considerable credit for doing something that had never been tried before. But here it is: a (temporarily) lost opportunity.

Click here for the details

For very large classes of HV/DS examples, the resulting jets-of-jets not only have many tracks but also have one or more of the following properties that are very unusual in ordinary jets:

• If their dark hadrons very often produce bottom quarks, which travel a tiny but measurable distance before they themselves decay to the hadrons we measure, a large fraction of the many tracks in the jet-of-jets will be “displaced”, meaning that they will not trace back precisely to the location of the proton-proton collision. [This too, is shown in Figure 19-20 of this paper.] Such a thing almost never happens in ordinary jets.
• If their dark hadrons themselves travel a tiny but measurable distance before they decay to ordinary hadrons or other Standard Model particles, then again a large fraction of the many tracks in the jet-of-jets will be displaced.
• If the dark hadrons in the dark jet very often decay to muons, or to bottom quarks and taus (which often subsequently decay to muons), then it will be common for a jet-of-jets to have three or more muons embedded within it. [This is observed in Table II of this paper, though in many HV/DS models the effect is even more dramatic.] While this is certainly not unheard of in ordinary jets, it is not at all typical.

And so, if one were to require not only many tracks but also many displaced tracks and/or several muons in each observed jet, then the fraction p of ordinary jets that would satisfy all these criteria would be substantially lower than it is in ATLAS’s current search, and the expected ND would be much smaller. This would then allow ATLAS to discover an even larger class of HV/DS models, ones whose jets-of-jets are significantly rarer or that produce somewhat fewer tracks, but make up for it with one of these other unusual features.

I hope that the experimenters at ATLAS (or CMS, if they try the same thing) will include these additional strategies the next time this method is attempted. Displaced tracks and embedded muons are very common in HV/DS jets-of-jets, and adding these requirements to the existing search will neither complicate it greatly nor make it more difficult for theorists to interpret. The benefit of much smaller background from ordinary jets, and the possibility of a discovery that the current search would have missed, seems motivation enough to me.

Congrats to ATLAS, and a Look Ahead

Let me conclude with a final congratulations to my ATLAS colleagues. Some physicists seem to think that if the LHC were creating particles not found in the Standard Model, we would know by now. But this search is a clear demonstration that such a viewpoint is wrong. Marked by simplicity and power, and easy to understand and interpret, it has reached deep into uncharted HV/DS territory using a strategy never previously tried — and it had the potential to make a discovery that all previous LHC searches would have missed.

Nor is this the end of the story; many more searches of the wide range of HV/DS models remain to be done. And they must be done; to fail to fully explore the LHC’s giant piles of data would be a travesty, a tremendous waste of a fantastic machine. Until that exploration is complete, using as many innovations as we can muster, the LHC’s day is not over.

The mathematician Roger Penrose has many accolades for his work in extending our perception of the universe. While his research dominates most reviews of him, author Patchen Barss has taken up the challenge of writing a biography about the life of Roger Penrose, who at 93 is still alive and active. In Barss’ book “The Impossible Man–Roger Penrose and the Cost of Genius” the reader gets a full appreciation of the life of a person who’s contributed so much.

Barss presents Penrose starting from his early childhood age. He grew up in the difficult times of World War 2 under the tutelage of well-to-do Quaker parents. The father dominated the family, resulting in Penrose not gaining much experience in understanding and dealing with emotions. But his father did teach him much about critical thinking and puzzle solving. Barss suggests that this nurturing played a key part in establishing Penrose’s skill and tenacity at mathematical problem solving.

One interesting aspect presented is that Penrose, being university chair of mathematics, was much more comfortable with geometries and shapes, rather than with equations. His penchant and ability to extend imagery beyond two, three and even four dimensions served him during his studies on special relativity and general relativity. Perhaps this was his genesis for postulating conditions at black hole singularities which, in part, garnered him the Nobel prize. Currently, he is still progressing toward a unified theory of spacetime as well as formulating the conformal cyclic cosmology (CCC) into an accepted conveyance.

While this biography provides a description of Penrose’s mathematics, such as light cones and tessellation, it does not provide details or proofs. For these, a reader can peruse any of the many books written by Penrose himself. Where this biography excels is in connecting personal moments and events with human interactions. There’s much about his wives and muses. There’s a constant stream of other high-calibre researchers who briefly or extensively interconnect. Many discussions describe his search for optimal working environments such as having a trapdoor lead to a garage converted into a private study. Unexpectedly, you can also read how Penrose colluded with Joe Rogan to promote his ideas.

As for many high achievers, any biography could become nearly unlimited in extent. This one was six years in the writing with Barss spending significant time directly interviewing the subject. It does present many momentous events including the killing of John Kennedy. But can a reader use it? Does it provide fodder for the debate of nature over nurture? Does it provide a prescription for becoming a chair of mathematics? Does it champion solitary contemplation or vouchsafe boisterous social conversing? That will be for the reader to discover.

Whichever your aim, the book “The Impossible Man–Roger Penrose and the Cost of Genius” by Patchen Barss is a solid biography. Penrose has made significant contributions to his field of expertise and continues hard at work. This book chiefly addresses how he does it. It’s easy to read and while not technical, it does provide an overview of the life of this many honored mathematician.

The post Book Review: The Impossible Man appeared first on Universe Today.

A team of astronomers have discovered a rather curious exoplanetary system that has two gas giant planets that are messing up each other’s orbit! On of them is 3.8 times the mass of Jupiter and completes an orbit every 82 days, the other is just 1.4 Jupiter masses. Hiding in the wings is another mini-Neptunian world. The two gas giants are locked into a 2:1 orbital resonance and, as a result of their gravitational interactions, the orbit of the more massive can vary by up to 4 days!

Exoplanets are alien worlds that orbit around stars beyond our Solar System. They vary by size, mass, composition and environment and studying them provides insight into not only planetary formation but also the liklihood for the presence of alien life! Like all bodies that orbit a common host; moons around a planet or planets around a star, their orbits can become linked in what has become known as a resonance.

This artist’s illustration shows the Neptune-like exoplanet GJ 3470b, which has an atmosphere rich in sulphur. The planet’s atmosphere holds clues to how it and other similar planets formed. Image Credit: Department of Astronomy, UW–Madison

Orbital resonance occurs when two or more orbiting bodies exert regular, periodic gravitational influence on each other, creating a stable orbital relationship. It often results in simple integer ratios between their orbital periods, such as 2:1 or 3:2. Neptune and Pluto for example are in a 2:3 resonance, meaning Pluto completes two orbits around the Sun for every three of Neptune’s. In our solar system, Jupiter’s moons Ganymede, Europa, and Io follow a 4:2:1 resonance, affecting their geological activity. Resonances help maintain orbital stability over long timescales but can also lead to instability in some cases, influencing planetary formation, migration, and even asteroid belt structures.

Kirkwood Gaps, histogram of asteroids as a function of their average distance from the Sun. Regions deplete of asteroids are called Kirkwood Gaps, and those bodies may have been escavated from the main belt owing to orbital resonances (image credit: Alan Chamberlain, JPL/Caltech).

The planetary system just discovered, TOI-4504 was detected by the Transiting Exoplanet Survey Satellite (TESS.) As TOI-4504 c orbits the star, they pass directly in front of the host star causing its light to dim in a transit event. It was this dimming that was spotted by TESS. The orbit of exoplanet TOI-4504 c is affected by the non-transiting planet TOI-4504 d. The gravitational interaction of this planet causes the transit times of TOI-4504 c to vary by about 4 days. The orbit of exoplanet TOI-4504 d does not cause a transit event but if its orbit were such that it did then the orbital period would vary by up to 6 days. 

Illustration of NASA’s Transiting Exoplanet Survey Satellite. Credit: NASA’s Goddard Space Flight Center

The lead author fo the paper, PhD student Michaela Vítková from the AI CAS in Czech Republic said “We were surprised to see such a large amplitude of the variations in the transit times of TOI-4504 c.”  The results of the study relied upon data not only from TESS but also from FEROS (Fibre-fed Extended Range Optical Spectrograph) on the 2.2m telescope at ESO’s La Silla observatory in Chile. The planetary system is a complex one with another 10 Earth-mass planet on an inner orbit that takes 2.4 days to complete one trip around the star.

The study reveals yet again what a fascinating study exoplanetary systems are. TOI-4504 is a great example of how varied the systems and their planets can be. The orbital resonances of planets ‘c’ and ‘d’ make for a fascinating system that would benefit from further study.

Source : Violent dance of massive gas giant planets

The post Massive Gas Giant Planets Locked in a Gravitational Struggle appeared first on Universe Today.

Saturn’s moon Titan is perhaps one of the most fascinating moons in the Solar System. It’s the second largest of all the moons in our planetary neighbourhood and is the only one with a significant atmosphere. It’s composed of 95% nitrogen and 5% methane and is 1.5 times as dense as the Earth’s atmosphere. The methane in the atmosphere of Titan is what puzzles scientists. It should have all be broken up within 30 million years causing the atmosphere to freeze but it hasn’t! There must be an internal process replenishing it, but what is it?

Titan is the largest moon of Saturn and second only in size to Ganymede, the largest moon of Jupiter. The surface of Titan is covered with dunes, icy mountains, and liquid hydrocarbon lakes—primarily composed of methane and ethane. Beneath its icy crust, scientists believe a vast subsurface ocean of water exists, raising the possibility of microbial life. NASA’s Cassini-Huygens mission provided detailed insights into Titan’s climate, seasonal changes, and its resemblance to early Earth, making it a target for future exploration.

Natural color image of Titan taken by Cassini in January 2012. (Credit: NASA/JPL-Caltech/Space Science Institute)

Dr. Kelly Miller from the South West Research Institute and Lead author of a paper about Titan’s atmosphere said “While just 40% the diameter of the Earth, Titan has an atmosphere 1.5 times as dense as the Earth’s, even with a lower gravity, walking on the surface of Titan would feel a bit like scuba diving!” To try and understand the existence of methane in the atmosphere Southwest Research Institute joined forces with the Carnegie Institution for Science to conduct some experiments with interesting results. 

ASA’s Cassini spacecraft looks toward the night side of Saturn’s largest moon and sees sunlight scattering through the periphery of Titan’s atmosphere and forming a ring of color. Credit: NASA/JPL-Caltech/Space Science Institute

A model was proposed in 2019 that suggested just how the methane could be replenished over the years. It theorised that large amounts of organic materials are heated by the moon’s interior, releasing nitrogen and carbon based gas like methane. The gas seeps to the surface where it replenishes the atmosphere. The theory was developed off the back of data from NASA’s Cassini-Huygens spacecraft which arrived at the Saturnian system in 2004. It explored it for the next 13 years while the Huygens probe dropped onto the surface of Titan in 2005. 

Artist depiction of Huygens landing on Titan. Credit: ESA

The team led by Miller arranged experiments to heat up organic materials to temperatures up to 500 degrees Celsius at pressures up to 10 kilobars. This simulated the conditions found under the surface of Titan. The process generated sufficient quantities of methane that would enable Titan’s atmosphere to be replenished to the levels we observe today. 

To learn more about the atmosphere of Titan, NASA plans to launch another spacecraft to the Saturnian system in 2028. It’s been called Dragonfly and involves a quadcopter that will, like Ingenuity did on Mars, explore Titan’s atmosphere. The thick atmosphere and low surface gravity make it an ideal place to explore from the air. Not only will it help us to understand more about the atmospheric conditions but it will help to assess the moon’s habitability by analysing prebiotic molecules and searching for signs of past, or even present life! 

Source : SwRI-designed experiments corroborate theory about how Titan maintains its atmosphere

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Join us for our 2nd Annual Skeptoid Adventure, this time to the Bermuda Triangle! Early bird pricing ends this Friday, don't miss the boat!

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Shrug, move on and never admit you were wrong

The post The willful blindness of RFK Jr’s supporters first appeared on Science-Based Medicine.

Investigators have identified in a preclinical model a specific brain circuit whose inhibition appears to reduce anxiety without side effects. Their work suggests a new target for treating anxiety disorders and related conditions and demonstrates a general strategy, based on a method called photopharmacology, for mapping drug effects on the brain.

Scientists developed advanced dating methods to track geological changes on the far side of the moon and found evidence of relatively recent activity.

A new article argues that by relying too much on parsimony in modeling, scientists make mistakes and miss opportunities.

The tiny protein known as transthyretin can cause big problems in the body when it misfolds after secretion. While healthy transthyretin moves hormones through blood and spinal fluid, misfolded versions of the protein form dangerous clumps in the heart and along nerves -- triggering a progressive and fatal disease known as transthyretin amyloidosis (ATTR). Up to a quarter of all men over the age of 80 have some degree of ATTR, which can cause shortness of breath, dizziness and tingling or loss of sensation in the extremities. Now, scientists have uncovered new structures of transthyretin.

In a groundbreaking achievement for quantum technologies, researchers have created a functional quantum register using the atoms inside a semiconductor quantum dot.

Researchers were able to demonstrate for the first time that non-covalent bonds between spin centers are also capable of producing quartet states through spin mixing. Supramolecular chemistry is thus a valuable tool for the research, development and scaling of new materials for quantum technologies.

Researchers were able to demonstrate for the first time that non-covalent bonds between spin centers are also capable of producing quartet states through spin mixing. Supramolecular chemistry is thus a valuable tool for the research, development and scaling of new materials for quantum technologies.

On Thursday January 30th, astronauts Suni Williams and Butch Wilmore are doing a 6.5-hour spacewalk outside the International Space Station. Among other goals, they’ll be collecting surface samples from the station to analyze for the presence of microbes.

The ISS “surface swab” is part of the ISS External Microorganisms project. It was developed to understand how microorganisms are transported by crew members to space. It also seeks to understand what happens to those “mini-critters” in the space environment.

The “bugs” that the two astronauts bring back in for analysis will come from areas on the space station near life-support system vents. The idea is to figure out if the station releases those microbes through the vents. Scientists also want to know the size of the release population, and where else they show up on the station.

The Microbes Experiment

Researchers seek to understand how microbes exist and thrive in space and planetary environments. At the moment, the best analog for those is on the ISS, particularly its exterior. So, when microbes find their way out, people want to know how long they survive the radiation. Do quick temperature changes affect them? What else happens to them? Also, scientists want to know if microbes manage to reproduce and how the environment changes that.

Samples from the ISS surface get frozen in special containers and eventually get returned to Earth. Once in the lab, they’re analyzed using culture-independent techniques such as next-generation deoxyribonucleic acid (DNA) sequencing to measure microbial community. Functional pathways in these microbial communities are characterized by targeting multi-gene analysis. This approach allows for a comprehensive assessment of the microbial diversity and metabolic function without cultivation. The samples collected at different locations or during different EVA opportunities allow investigators to map the microbial diversity of ISS external surfaces.

A member of the ISS External Microorganisms payload development team demonstrates removing a swab from the sampling caddy that is used by an astronaut during a spacewalk. A crew member uses the swabbing tool to collect microbes in samples from the exterior surface of the International Space Station at various locations. Results could inform preparations for future human exploration missions to the Moon and Mars. Credit: NASA. Why Test for Microbes?

While people have been flying to and from space for decades now, the scientific community still has significant gaps in knowledge about understanding how microbes get released, how they thrive, and what their life cycles are in space. In particular, the ISS sees many visiting vehicles each year, and astronauts move around freely inside. Those activities likely increase the microbe population both inside and out.

Collecting microbes and analyzing them allows scientists to assess the types and numbers of microorganisms living on the outer shell of a spacecraft. The larger goal is to supply more information under the guidelines of NASA’s policy on Planetary Protection Requirements for Human Extraterrestrial missions. There are still many questions to be answered, including: what are the acceptable levels of microbial life? Which ones make it out through the vents? What are acceptable contamination rates? While NASA has designed this mission to answer those and other questions, the Russian space agency Roscosmos is also making similar investigations to sample the Russian side of the station. That resulted in the discovery of non-spore-forming bacteria growing on the outer skin of the station.

The results of microbe analysis from this and other microorganism collections could affect spacecraft design and spacesuit changes. This becomes doubly important when people venture out onto the surface of Mars, for example. While we see no direct evidence of life there now, it could be there and likely existed in the past. Not only do we want to avoid contaminating astronauts with that life, we also want to avoid (as much as possible) bringing Earth life to Mars. This same research has applications in other fields, such as agriculture and pharmaceuticals.

Info on the Space Walk

This isn’t the first time the ISS has been tested for exterior microbial life, and the long-term study is necessary. The planned sampling to be mission undertaken by Williams and Wilmore is officially called Spacewalk 92 and should start at 8 a.m. on January 30th. NASA will provide live coverage of the walk (check here for more information), which will also conduct some other maintenance on the station along with the sampling activities.

For More Information

Astronauts Set to Swab the Exterior of Station for Microbial Life
Space Station Research Explorer

The post Astronauts are Going to Check if There are Microbes on the Outside of the Station appeared first on Universe Today.

When an exoplanet is discovered, scientists are quick to describe it and explain its properties. Now, we know of thousands of them, many of which are members of a planetary system, like the well-known TRAPPIST-1 family of planets.

Patterns are starting to emerge in these exoplanetary systems, and in new research, a team of scientists says it’s time to start classifying exoplanet systems rather than just individual planets.

The paper is “Architecture Classification for Extrasolar Planetary Systems,” and it’s available on the pre-print site arxiv.org. The lead author is Alex Howe from NASA’s Goddard Space Flight Center. The authors say it’s time to develop and implement a classification framework for exoplanet systems based on our entire catalogue of exoplanets.

“With nearly 6000 confirmed exoplanets discovered, including more than 300 multiplanet systems with three or more planets, the current observational sample has reached the point where it is both feasible and useful to build a classification system that divides the observed population into meaningful categories,” they write.

The authors explain that it’s time for a systemic approach to identifying patterns in exoplanet systems. With almost 6,000 exoplanets discovered, scientists now have the data to make this proposition worthwhile.

Artist’s rendition of a variety of exoplanets featured in the new NASA TESS-Keck Survey Mass Catalog, the largest, single, homogenous analysis of TESS planets released by any survey thus far. Credit: W. M. Keck Observatory/Adam Makarenko

What categories do the authors propose?

The first step is necessarily broad. “The core of our classification system comes down to three questions for any given system (although, in several cases, we add additional subcategories). Does the system have distinct inner and outer planets?” the authors write.

Next comes the question of Jupiters. “Do the inner planets include one or more Jupiters?” After that, they ask if the inner planets contain any gaps with a period ratio greater than 5. That means if within the gaps between the inner planets, are there any instances where the ratio of the orbital periods of two hypothetical planets occupying those gaps would exceed 5? Basically, that boils down to asking if the absence of planets in specific regions in the inner solar system is related to unstable orbits.

These three questions are sufficient to classify nearly all of the exoplanet systems we’ve discovered.

“We find that these three questions are sufficient to classify ~97% of multiplanet systems with N ?3 planets with minimal ambiguity, to which we then add useful subcategories, such as where any large gaps occur and whether or not a hot Jupiter is present,” the authors write.

The result is a classification scheme that divides exoplanet systems into inner and outer regimes and then divides the inner regimes into dynamical classes. Those classes are:

• Peas-in-a-pod systems where the planets are uniformly small
• Warm Jupiter systems containing a mix of large and small planets
• Closely-space systems
• Gapped systems

There are further subdivisions based on gap locations and other features.

“This framework allows us to make a partial classification of one- and two-planet systems and a nearly complete classification of known systems with three or more planets, with a very few exceptions with unusual dynamical structures,” the authors explain.

In summary, the classification scheme first divides systems into inner and outer planets (if both are detected). Systems with more than three inner planets are then classified based on whether their inner planets include any Jupiters and whether (and if so, where) their inner planets include large gaps with a period ratio >5. Some systems have other dynamical features that are addressed separately from the overall classification system.

This is a quick reference chart for the new system of classifying planetary system architectures, with representative model systems for each category. Each row is one planetary system, where the horizontal spacing corresponds to the orbital period, and the point sizes correspond to planet sizes. Colours correspond to planet type: Jupiters (>6 Earth radii, red), Neptunes (3.5-6 Earth radii, gold), Sub-Neptunes (1.75-3.5 Earth radii, blue), and Earths (<1.75 Earth radii, green). Image Credit: Howe et al. 2025.

The classification system is based on NASA’s Exoplanet Archive, which listed 5,759 exoplanets as of September 2024. It’s a comprehensive archive, but it also contains some questionable exoplanets drawn from papers that can sometimes be inaccurate, poorly constrained, or even contradicted by subsequent papers. The researchers filtered their catalogue to remove data they considered unusable. As a result, they removed 2% of the exoplanets in their archive.

They also filtered out some of the stars because of incomplete data, which meant that planets around those stars were removed, too. Planets orbiting white dwarfs and pulsars were removed, as were planets orbiting brown dwarfs. The idea was to “represent the population of planets orbiting main sequence stars,” as the authors explain.

This table from the research shows the number of confirmed planetary systems by multiplicity after the researchers applied all of their filters. Image Credit: Howe et al. 2025.

As the table above makes clear, most exoplanet systems contain only a single detected planet. 78% of them host only one planet, often a hot Jupiter, though selection effects play a role in the data. Jupiters are a key planet type in nature and in the classification scheme.

“As expected, Jupiter-sized planets are far less likely to occur in multiplanet systems at periods of <10 days and virtually none do at <5 days, as indicated by the near-coincidence of the two Jupiter distributions at those periods. Meanwhile, roughly half of all other planet types and even a third of Jupiters at periods >10 days occur in multiplanet systems,” the authors explain.

This figure shows the cumulative distributions of confirmed exoplanets with orbital periods. It compares the total numbers of planets (dashed) to those in single-planet systems (solid). “Hot Jupiters show far fewer companions than other planet types, as illustrated by the near-coincidence of the two Jupiter distributions at <10 days,” the authors explain.

The classification system does a good job of capturing the large majority of exoplanet system architectures. However, there are some oddballs, including the WASP-148 system, the only known system with a hot Jupiter and a nearby Jupiter companion. “Given the high detection probability of such a companion and the fact that 10 hot Jupiters are known to have smaller nearby companions, this points to an especially rare subtype of system and potential unusual migration processes,” the authors write.

This table presents the seven oddballs in NASA’s Exoplanet Archive according to the classification scheme. Image Credit: Howe et al. 2025.

Though exoplanet systems seem to be very diverse, this classification scheme shows that there’s a lot of uniformity in the patterns. Even though there’s a large diversity of planet types, most inner systems are either peas-in-a-pod systems or warm Jupiter systems. “Only a tiny minority of N ?3 systems (9 out of 314) prove difficult to classify into one of these two categories,” the authors write.

Like much exoplanet science, this system is hampered by detection biases. We struggle to detect small planets like Mars with our current capabilities. There could be more of them hiding in observed exoplanet systems. There are more detection problems, too, like planets on long orbits. However, the scheme is still valuable and interesting.

“This classification scheme provides a largely qualitative description of the architectures of currently observed multiplanet systems,” the authors explain. “The next step is to understand how such systems are formed, and, perhaps equally important, why other dynamically plausible systems are not present in the database.”

One outcome concerns the peas-in-a-pod systems. Since they’re so prevalent, scientists are keen to develop theories on their formation.

The system also has implications for habitability. The outcomes show that in peas-in-a-pod systems, the planets are often too close to main sequence stars to be habitable. Conversely, these same types of systems around M-dwarfs likely have planets in their stars’ habitable zones. “This may suggest that the majority of habitable planets reside around lower-mass stars in peas-in-a-pod systems,” the authors explain. That brings up the familiar problem of flaring and red dwarf habitability.

Another problem this classification scheme highlights concerns super-Earth habitability. “Most planets in peas-in-a-pod systems are super-Earths, rather than Earth-sized, and may be too large for the canonical definition of a habitable planet,” the authors write.

In their conclusion, the researchers explain that exoplanet systems seem to have clear organizing principles that we can use to classify distinct types of solar systems.

“Though far from complete, we believe this classification provides a better understanding of the population as a whole, and it should be fertile ground for future studies of exoplanet demographics and formation,” the researchers conclude.

The post It’s Time to Start Classifying Exoplanetary Systems appeared first on Universe Today.

I thought I was clever when I decided that an alternative word for a woke person could be a “Passive Progressive”, but then was told that woke people aren’t passive because they create a lot of noise and kerfuffle. I still like my new term, though, as by “passivity” I meant “performativeness”.  That is, a woke person espouses progressive Leftist ideals but does not do anything to enact them, ergo the passivity.

But I digress. While poring through some scientific literature yesterday, I came upon an issue of The American Naturalist from July 2022. This used to be one of the go-to journals for publishing evolutionary biology, and I was a corresponding editor for a while, but in my view it’s slipped a bit. This issue, with its special section on “Nature, data, and power” is about as ideologically captured as you can get. And this was three years ago! Well, capture started well before that. If you want to read any of these articles, just click on the screenshots below (there are two because the section is so long. There are other real science papers not soaked in politics, but I haven’t put them down.

Which paper is your favorite?

 

Doctors who mourned the loss of a single speech or YouTube video are fine with the the mass censorship of public scientists.

The post Well Well Well, We Want Them Infected Doctors Are OK With Censorship After All first appeared on Science-Based Medicine.

Boom Supersonic’s XB-1 aircraft broke the sound barrier during three test runs, a step toward the possible return of supersonic commercial flights

Astronomers have found some pretty wild exoplanets. Some are balls of lava the temperature of hell, one is partially made of diamond, and another may rain molten iron. However, not all exoplanets are this extreme. Some are rocky, roughly Earth-sized worlds in the habitable zones of their stars.

Could simple Earth life survive on some of these less extreme worlds?

We currently describe a solar system’s habitable zone by liquid water. If a planet is at the right distance range from its star to host stable surface water, we consider it to be in the habitable zone. However, new research is taking a different approach by emphasizing the role a planet’s atmosphere plays in habitability.

The scientists behind this research tested their idea by seeing if microbes could survive on simulated worlds.

The new research is “The Role of Atmospheric Composition in Defining the Habitable Zone Limits and Supporting E. coli Growth.” It’s available on the pre-print site arxiv.org. The lead author is Asena Kuzucan, a post-doctoral researcher in the Department of Astronomy at the University of Geneva in Switzerland.

We’ve discovered close to 6,000 exoplanets in about 4,300 planetary systems. Our burgeoning catalogue of exoplanets makes us wonder about life. Is there life elsewhere, and are any of these thousands of exoplanets habitable?

Some have teased the possibility. TRAPPIST1-e and Proxima Centauri b are both rocky planets in the habitable zones of their stars. TOI-700 d orbits a small, cool star and may be in its habitable zone. There are many others.

The simple definition of the habitable zone is restricted to a planet’s distance from its star and if liquid water can persist on its surface at that distance. However, scientists know that a planet’s atmosphere plays a large role in habitability. A thick atmosphere on a planet outside the habitable zone could help it maintain liquid water.

“Each atmosphere uniquely influences the likelihood of surface liquid water, defining the habitable zone (HZ), the region around a star where liquid water can exist,” the authors write. Liquid water doesn’t guarantee that a world is habitable, however. In order to understand exoplanet habitability better, the researchers followed a two-pronged approach.

They started by estimating exoplanet surface conditions near the inner edge of a star’s HZ with different atmospheric compositions.

Next, they considered if Earth microbes could survive in these environments. They did lab experiments on E. coli to see how or if they could grow and survive. They focused on the different compositions of gas in these atmospheres. The atmospheric compositions were standard (Earth) air, pure CO2, N2-rich, CH4-rich, and pure molecular hydrogen.

Their experiments used 15 separate bottles, 3 for each of the 5 atmospheric compositions. Each bottle was inoculated with E. coli K-12, a laboratory strain of E. coli that is a cornerstone of molecular biology studies.

This simple graphic shows the atmospheric composition of the test bottles. Each bottle is a combination of different atmospheric composition and pressure. LB stands for Lysogeny broth, a nutrient source for E. coli K12. image Credit: Kuzucan et al. 2025.

“This innovative combination of climate modelling and biological experiments bridges theoretical climate predictions with biological outcomes,” they write in their research.

Along with their laboratory experiments, the team performed a series of simulations with different atmospheric compositions and planetary characteristics. “For each atmospheric composition we simulate, water is a variable component that can condense or evaporate as a function of the pressure/temperature conditions,” they write. For each atmospheric composition, they simulated planets at different orbital distances in order to define the inner edge of the HZ. They also varied the atmospheric pressure.

“Using 3D GCM (General Circulation Model) simulations, this study provides a first look at how these atmospheric compositions influence the inner edge of the habitable zone, offering valuable insights into the theoretical limits of habitability under these extreme conditions,” the authors explain.

This table from the research shows the planetary and stellar characteristics used in the GCM simulations. Image Credit: Kuzucan et al. 2025.

“Our findings indicate that atmospheric composition significantly affects bacterial growth patterns, highlighting the importance of considering diverse atmospheres in evaluating exoplanet habitability and advancing the search for life beyond Earth,” they write.

This figure shows the cell count for E. coli K12 in each simulated atmosphere. Image Credit: Kuzucan et al. 2025.

E. coli did surprisingly well in varied atmospheric compositions. Though there was a lag following inoculation as the E. coli adapted, cell density increased in some of the tests. The hydrogen-rich atmosphere did surprisingly well.

“By the first day after inoculation, cell densities had increased in standard air, CH4-rich, N2-rich, and pure H2 atmospheres,” the authors write. “While cell densities increased similarly in standard air, CH4-rich, and N2-rich atmospheres, a slightly stronger increase was observed in the pure H2 atmosphere. The rapid adaptation of E. coli to pure H2 suggests that hydrogen-rich atmospheres can support anaerobic microbial life once acclimatization occurs.”

Conversely to the H2 results, the CO2 results lagged. “Pure CO2, however, consistently presented the most challenging environment, with significantly slower growth,” the paper states.

Their results suggest that planets with anaerobic atmospheres that are dominated by H2, CH4, or
N2 could still support microbial life, even if the initial growth is slower than it is in Earth’s air. “The ability to adapt to less favourable conditions implies that life could persist on such planets, given sufficient time for acclimatization,” the authors write.

The CO2-rich atmosphere is the outlier in this work. “The consistently poor growth in pure CO2 highlights the limitations of this gas in supporting life, particularly for heterotrophic organisms like E. coli,” Kuzucan and her co-researchers write. However, the authors point out that some life forms can make use of CO2 as a carbon source in some environments. They explain that planets with these types of atmospheres could still host organisms adapted to them, like chemotrophs or extremophiles.

This work combines atmospheric and biological factors to understand exoplanet HZs. “One of our key objectives was to define the limits of the HZ for planets dominated by H2 and CO2 using 3D climate modelling, specifically the Generic PCM model,” the authors explain.

They found that H2 atmospheres have a warming effect, “pushing the inner edge of the HZ to further orbital distances than CO2-dominated atmospheres.” It could extend out to 1.4 AU at 5 bar, while the CO2 atmospheres at the same pressure were limited to 1.2 AU. “This demonstrates the profound impact of atmospheric composition on planetary climate and highlights how H2 atmospheres can extend the
habitable zone further from their host stars,” the researchers write.

Some of the atmospheres they tested are not likely to persist in nature, but the results are still scientifically valuable.

“Although some of the atmospheric scenarios presented here (1-bar H2 and CO2) are simplified, and
may not persist over geological timescales due to processes like hydrogen escape and carbonate-silicate cycling, they nonetheless provide valuable insights into the radiative effects of these gases on habitability,” write the authors.

We know atmospheres are extremely complex, and this research supports that. It also shows how resilient Earth life can be. “Overall, these results highlight both the resilience of E. coli in adapting to diverse atmospheric conditions and the critical role atmospheric composition plays in determining
microbial survival,” the authors explain in their conclusion. Though the authors acknowledge that their findings are rooted in an Earth-centric framework, the results have broader implications. Life could likely thrive in wildly different atmospheric compositions and conditions, according to these results.

“Thus, our study highlights the importance of atmospheric composition and pressure for habitability while acknowledging the limitations of our Earth-centric perspective,” they write.

“By exploring both atmospheric conditions and microbial survival, we gain a deeper understanding of the complex factors that influence habitability, paving the way for future research on the potential for life beyond our solar system.”

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