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.
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:
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.
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.
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.
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.
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.
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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 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.
“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.
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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The event horizon is a fascinating part of a black hole’s anatomy. In 2017, telescopes around the world gathered data on the event horizon surrounding the supermassive black hole at the heart of M87. This was the first time we had ever seen an image of such a phenomenon. Since then, 120,000 more images of the region have been captured and, as astronomers sift through the data, their model of M87’s event horizon has evolved.
Black holes, formed from the collapse of massive stars or in some cases through other processes, are regions of space-time where gravity is so intense that it warps the fabric of the universe. The event horizon is the boundary surrounding a black hole, beyond which nothing—not even light—can escape its gravitational pull. It marks the point of no return for any matter or radiation that gets too close. Within the event horizon, the curvature of space-time becomes infinite, leading to a singularity, a point where density and gravity reach extremes that modern physics and mathematics struggle to model. The event horizon’s properties are critical to understanding black holes, as it represents the outermost layer hiding everything within.
One such object sits at the centre of most galaxies and in particular at the centre of M87, a massive elliptical galaxy 53 million light years away. It’s approximately 120,000 light years across with an estimated trillion stars. At its core is a supermassive black hole which weighs in at about 6.5 billion times the mass of the Sun. It was this object which was imaged back in 2017 for the first time.
Since that first image of the event horizon around the M87 black hole, over 120,000 images have been used to analyse how the horizon has evolved since the first images were captured. Like all black holes, M87’s has a rotational axis and it is this, that the images have revealed something unexpected.
A team of astronomers have confirmed that the axis points away from the Earth and have shown that the accretion disk suffers turbulence. Compared to images from 2017, the accretion disk has brightened and it is thought the turbulence in the accretion disk is the cause. As assistant professor Hung-Yi Pu from National Taiwan Normal University explains “the black hole accretion environment is turbulent and dynamic. Since we can treat the 2017 and 2018 observations as independent measurements, we can constrain the black hole’s surroundings with a new perspective.”
The accretion disk around M87* (as the black hole is referred to) is a swirling disk of gas and dust that orbits around the black hole before being pulled in. The disk forms when matter is stripped off nearby stars or from interstellar gas before spiralling in to the black hole under its immense gravitational pull. As the material accelerates in the disk and gets compressed, it heats up to millions of degrees, emitting radiation across the electromagnetic spectrum. It’s this radiation that often reveals the presence of a black hole.
The discoveries from the super computer generated images reveal more about the dynamics in the regions surrounding a black hole. They find that material spiralling into a black hole from afar can either flow in the direction of the black hole’s rotation or in the opposite direction.
Source : M87 One Year Later: Catching the Black Hole’s Turbulent Accretion Flow
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A classic scene from several high sci-fi movies and shows is when the characters approach their new spaceship in space for the first time. It is typically attached to a massive structure – think of the Kuat Drive Yards in Star Wars or the Utopia Planitia Fleet Yards around Mars in Star Trek. These gigantic structures play a role akin to what dry docks do for modern navies – they allow for the construction of ships in a relatively controlled environment with access to tools and equipment specialized for their construction. That is the idea behind a new NASA Institute for Advanced Concepts (NIAC) grant to ThinkOrbital, a company specializing in In-space assembly, manufacturing, and construction (ISAM&C). Their idea is to build a “Construction Assembly Destination” in orbit to build spacecraft in space.
That might seem like a lofty goal, but ThinkOrbital has some pedigree in doing ISAM&C tasks that no one else has done before. In May 2024, they launched and successfully tested the first-ever weld in space. The mission flew on a Falcon 9, spot-welded together some quarter-inch pieces of aluminum, and returned it to Earth, where the welds were closely examined.
They used a method called electron beam welding, which has several advantages for use in space. First, it doesn’t require as much power as a traditional arc welder—only around 2KW, equivalent to a household iron. Second, it doesn’t create a lot of heat, which can degrade the metal being welded and cause issues like splintering, which can become dangerous in zero-gravity situations.
Doing a simple weld is a far cry from building an entire floating dry dock, but it is a step in that direction. Vojtech Holub, ThinkOrbital’s co-founder and CIO, said in an interview with Fraser that the company had actually submitted a proposal to NIAC for a more moderate step in the development of ISAM&C technology. However, the idea for a space station four times the size of the ISS “was not deemed futuristic enough.”
That rejection inspired the company to go bigger – by suggesting an entire orbital construction platform. In the interview, Dr. Volub talks about creating an interior space of 4,000 cubic meters by launching exterior plates akin to the hexagons on a soccer ball and welding them together in space using the company’s existing welder technology. In theory, if the process can be repeated, you could even build a large enough station to make something “up to [the size of] an Imperial Star Destroyer,” according to Dr. Holub.
There are some obvious difficulties in scaling up to that level, including requiring thicker plates and how to introduce gravity to any human occupants. Still, the general idea is scalable well beyond anything currently in orbit. As part of the NIAC grant, Dr. Holub and his team will have to develop a concept of operations (or CONOPS) for the development of the station, including how many launches it would take, what kind of structural loads it would be under, and how it would be assembled once it was up there.
With answers to those questions in hand, ThinkOrbital would potentially be given a Phase II NIAC grant that would allow them to start building some prototypes to de-risk the technology. But they’ve got to complete Phase I first and compete with plenty of other ideas that NIAC has selected. If they are picked for a Phase II grant, though, it could move the start-up from concept to the reality of building a massive space for constructing space infrastructure – something humanity will need when it expands more throughout the solar system.
Learn More:
NASA / ThinkOrbital – Construction Assembly Destination
Vojtech Holub – Orb2: Spherical Space Station Designed for Single Launch and On-Orbit Assembly
UT – Blue Origin Announces the “Orbital Reef,” the Space Station they Plan to Build in Orbit
UT – Gateway Foundation Gives a Detailed Update on its Voyager Station Concept
Lead Image:
Artist concept highlighting the novel approach proposed by the 2025 NIAC awarded selection of Construction Assembly Destination
Credit – NASA/Ryan Benson/ThinkOrbital
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Exoplanets have captured the imagination of public and scientists alike and, as the search continues for more, researchers have turned their attention to the evolution of metallicity in the Milky Way. With this answer comes more of an idea about where planets are likely to form in our Galaxy. They have found that stars with high-mass planets have higher metallicity than those with lower amounts of metals. They also found that stars with planets tend to be younger than stars without planets. This suggests planetary formation follows the evolution of a galaxy with a ring of planet formation moving outward over time.
The search for exoplanets has largely been one of surveying nearby stars. That generally means we are exploring stars in our region of the Galaxy. As technology develops, our ability to detect them improves and to date, nearly 6,000 planets have been discovered around other stars. A number of different techniques have been used to find them such as the transit method – which detects the dimming of a star’s light due to the presence of the passage of a planet, or the radial velocity method which measures the wobble of a star due to the gravitational tug of a planet.
One key aspect of planetary development in the Galaxy is the presence of metals (elements heavier than hydrogen and helium.) known as metallicity. These elements are formed during the life cycle of a star, especially during supernova explosions. They are scattered through space and form part of the interstellar medium. Understanding the abundance and distribution of metals provides an insight into the age, history and formation rates of stars and planets.
A team of researchers led by Joana Teixeira from the University of Porto in Portugal have been exploring something known as the Galactic Birth Radii (rBirth) This term relates to the distance from galactic centre that stars and therefore planets are forming. Using photometric, spectroscopic and astrometric data, the team were able to estimate the ages of two groups of stars, those with planets and those without. This enabled them to rBirth for exoplanets based upon the original star positions (having calculated them from their age and levels of metals present within.)
The results of the analysis showed that stars hosting planets had a higher [Fe/H], are younger and were born closer to the centre of the galaxy than those without (Fe/H refers to the amount of iron relative to the amount of hydrogen in a star or galaxy, where the Sun is [Fe/H]=0.3.) The team went further to state that from one data set (from the Stellar Parameters of Stars with Exoplanets Catalog,) the results suggest that stars hosting high mass planets have a different iron to hydrogen radio and age distribution than stars with at least one low mass planet and those with only low mass planets.
The research reveals that high mass planets or in other words terrestrial planets tend to form around stars with higher [Fe/H] and younger stars compared to low mass. Similarly, those with a mixture of high and low mass planets also formed around higher [Fe/H], young stars.
It’s an interesting study worthy of further investigations. Understanding that Earth-like planets tend to form around star systems that formed around the inner regions of the Galaxy. Here the supply of metals is more abundant and, even though the stellar systems can migrate to outer regions of the Milky Way it gives a better focus on the hunt for planetary systems beyond our own.
Source : Where in the Milky Way Do Exoplanets Preferentially Form?
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Astronomers have found two planets around two separate stars that are succumbing to their stars’ intense heat. Both are disintegrating before our telescopic eyes, leaving trails of debris similar to a comet’s. Both are ultra-short-period planets (USPs) that orbit their stars rapidly.
These planets are a rare sub-class of USPs that are not massive enough to hold onto their material. Astronomers know of only three other disintegrating planets.
USPs are known for their extremely rapid orbits, some completing an orbit in only a few hours. Since they’re extremely close to their stars, they’re subjected to intense heat, stellar radiation, and gravity. Many USPs are tidally locked to their star, turning the star-facing side into an inferno. USPs seldom exceed two Earth radii, and astronomers think that about 1 in 200 Sun-like stars has one. They were only discovered recently and are pushing the boundaries of our understanding of planetary systems.
There are plenty of unanswered questions about USPs. Their formation mechanism is unclear, though they likely migrated to their positions rather than formed there. They’re difficult to observe because of their proximity to their stars, making questions about their structures difficult to answer.
Fortunately, two separate teams of researchers have spotted the two disintegrating USPs. As they spill their contents out into space in tails, they’re giving astronomers an opportunity to see what’s inside them.
The new observations are in two new papers available at the pre-press site arxiv.org. One is “A Disintegrating Rocky Planet with Prominent Comet-like Tails Around a Bright Star.” The lead author is Marc Hon, a postdoctoral researcher at the MIT TESS Science Office. This paper is referred to hereafter as the MIT study.
“We report the discovery of BD+054868Ab, a transiting exoplanet orbiting a bright K-dwarf with a period of 1.27 days,” the authors write. The TESS spacecraft found the planet, and its observations “reveal variable transit depths and asymmetric transit profiles,” the paper states. Those are characteristics of dust coming from the doomed planet and forming tails: one on the leading edge and one on the trailing edge. Dust particle size in each tail is different, with the leading trail containing larger dust and the trailing tail containing finer grains.
“The rate at which the planet is evaporating is utterly cataclysmic, and we are incredibly lucky to be witnessing the final hours of this dying planet’,'”
Marc Hon, MIT TESS Science Office
“The disintegrating planet orbiting BD+05 4868 A has the most prominent dust tails to date, “said lead author Hon. “The dust tails emanating from the rapidly evaporating planet are gigantic. Its length of approximately 9 million km encircles over half the planet’s orbit around the star every 30 and a half hours,” he added.
The MIT study shows that the planet is losing mass at the rate of 10 Earth masses of material per billion years. Since the object is probably only roughly the size of Earth’s Moon, it will be totally destroyed in only a few million years. “The rate at which the planet is evaporating is utterly cataclysmic, and we are incredibly lucky to be witnessing the final hours of this dying planet,” said Hon.
The host star is probably a little older than the Sun and has a companion red dwarf separated by about 130 AU. The authors think that the planet is a great candidate for follow-up studies with the JWST. Not only is the star bright, but the transits are deep. Because of the leading and trailing tails, the transits can last up to 15 hours.
“The brightness of the host star, combined with the planet’s relatively deep transits (0.8?2.0%), presents BD+054868Ab as a prime target for compositional studies of rocky exoplanets and investigations into the nature of catastrophically evaporating planets,” they explain.
“What’s also highly exciting about BD+05 4868 Ab is that it has the brightest host star out of the other disintegrating planets —about 100 times brighter than K2-22—establishing it as a benchmark for future disintegrating studies of such systems,” said Avi Shporer, a Research Scientist at the MIT Kavli Institute for Astrophysics and Space Research and a co-author of the MIT paper. “Prior to our study, the three other known disintegrating planets were around faint stars, making them challenging to study,” he added.
The second paper is “A Disintegrating Rocky World Shrouded in Dust and Gas: Mid-IR Observations of K2-22b using JWST.” The lead author is Nick Tusay, a PhD student at Penn State working in the Center for Exoplanets and Habitable Worlds. This paper is hereafter referred to as the Penn State study.
“The effluents that sublimate off the surface and condense out in space are probably representative of the formerly interior layers convectively transported to the molten surface,” the authors write. In this work, astronomers were able to observe its debris with the JWST’s MIRI and also with other telescopes. The observations show that the material coming from the USP is not likely to be iron-dominated core material. Instead, they’re “consistent with some form of magnesium silicate minerals, likely from mantle material,” the authors explain.
“These planets are literally spilling their guts into space for us, and with JWST we finally have the means to study their composition and see what planets orbiting other stars are really made of,” said lead author Tusay.
We can’t see what’s inside the planets in our Solar System, though seismic waves and other observations give scientists a pretty good idea about Earth’s interior. By examining the entrails coming from K2-22b, astronomers are learning not only about the planet but, by extension, about other rocky planets. The irony is that they’re so far away.
“K2-22b has an asymmetric transit profile, as the planet’s dusty cloud of effluents comes into view in front of the star, showing evidence of extended tails like a comet.”
“It’s a remarkable and fortuitous opportunity to
Professor Jason Wright, Astronomy and Astrophysic, Penn State
understand terrestrial planet interiors.”
“It’s remarkable that directly measuring the interior of planets in the Solar System is so challenging—we have only limited sampling of the Earth’s mantle, and no access to that of Mercury, Venus, or Mars—but here we have found planets hundreds of light years away that are sending their interiors into space and backlighting them for us to study with our spectrographs,” said Jason Wright, Professor of Astronomy and Astrophysics, co-author of the Penn State study, and Tusay’s PhD supervisor. “It’s a remarkable and fortuitous opportunity to understand terrestrial planet interiors,” he added.
While TESS discovered the disintegrating planet in the previous paper, Kepler found this one during its extended K2 mission. This one orbits its M-dwarf star in only 9.1 hours. Evidence of its tail is in the variability of its light curve. “The dramatic variability in lightcurve transit depth (0–1.3%) combined with the asymmetric transit shape suggests we are observing a transient cloud of dust sublimating off the surface of an otherwise unseen planet,” the MIT paper states.
According to the authors, this could be the first time we’ve seen outgassing from a vaporizing planet. “The shorter MIRI wavelength features … may constitute the first direct observations of gas features from an evaporating planet,” the paper states.
“Unexpectedly, the models that best fit these measurements seem to be ice-derived species (NO and CO2),” the authors write. Though the spectrum is broadly consistent with a rocky body, the presence of NO and CO2 is a bit of a curveball. These materials are more similar to icy bodies like comets rather than rocky planets.
“It was actually sort of a ‘who-ordered-that?’ moment,” Tusay said about finding the icy features. For this reason, the researchers are eager to point the JWST at the planet again to obtain more and better data. Multiple pathways can generate these results, and only better data can help astronomers determine what’s going on.
Though we’re in the early days of observing planets like this one, scientists still have some expectations. These results defy those expectations since many expected to find only the iron-core remnants of these USPs.
“We didn’t know what to expect,” said Wright, who also co-authored an earlier study on how to use JWST to probe these exoplanetary tails. “We were hopeful they might still have their mantles, or potentially even crust material that was being evaporated. JWST’s mid-infrared spectrograph MIRI was the perfect tool to check, because crustal, silicate mantle, and iron core materials would all transmit light in different ways that JWST could distinguish spectroscopically,” Wright added.
Next, both teams of scientists hope to point the JWST at BD+05 4868 Ab from the MIT study. Its star is far brighter than the other stars known to host disintegrating USPs. A bright light source makes it much easier for the JWST to get stronger results.
“What’s also highly exciting about BD+05 4868 Ab is that it has the brightest host star out of the other disintegrating planets —about 100 times brighter than K2-22—establishing it as a benchmark for future disintegrating studies of such systems,” said Avi Shporer, a Research Scientist at the MIT Kavli Institute for Astrophysics and Space Research and a co-author of the MIT project. “Prior to our study, the three other known disintegrating planets were around faint stars, making them challenging to study,” he added.
When the JWST was launched, it wasn’t aimed at observing disintegrating exoplanets. But this research shows off a new way of using the powerful telescope. Surprises like this are a part of every new telescope or observing effort, and researchers often look forward to them.
“The data quality we should get from BD+05 4868 A will be exquisite,” said Shporer. “These studies have proven the validity of this approach to understanding exoplanetary interiors and opened the door to a whole new line of research with JWST.”
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Exoplanet exploration has taken off in recent years, with over 5500 being discovered so far. Some have even been in the habitable zones of their stars. Imaging one such potentially habitable exoplanet is the dream of many exoplanet hunters, however, technology has limited their ability to do that. In particular, one specific piece of technology needs to be improved before we can directly image an exoplanet in the habitable zone of another star – a starshade. Christine Gregg, a researcher at NASA Ames Research Center, hopes to contribute to the effort of developing one and has received a NASA Institute for Advanced Concepts (NIAC) grant as part of the 2025 cohort to work on a star shade that is based on a special type of metamaterial.
To understand the goal of Dr. Gregg and her team, it’s best first to understand what starshades do and what’s holding them back from being deployed. A starshade is designed to float in tandem with a space telescope and block out the light from a specific star, allowing the telescope to capture light directly from the much-less bright planet that is orbiting the star. That light can contain information about its size, orbital period, and even its atmospheric composition that would otherwise be lost in the overwhelming brightness of the planet’s star.
The shape of a starshade, which traditionally looks like a flower petal, might seem counterintuitive at first – if you’re trying to block a star’s light, why not just make the shape circular? But starlight coming from far away can diffract around a simple circle structure. The petals are explicitly designed to stop that from happening and completely block out even diffracted light around the shape’s edges.
But it’s not the shape that makes it hard to deploy—it’s its size. Starshades are typically designed to be hundreds of meters across. Therefore, they are impossible to fit inside a traditional rocket fairing fully assembled. What’s more, they have to move along with the telescope—if the telescope the starshade is meant to accompany is pointed at another star and redirected, the starshade has to move with it.
The wrinkle is that the starshade is likely tens of thousands of kilometers from the telescope it is designed to assist. So, a slight change of a few degrees of inclination for the telescope would mean hundreds of thousands of kilometers of travel for its associated starshade. That kind of movement requires a lot of fuel, which is also costly due to the weight requirements of launching these objects so far away.
No wonder a starshade has yet to be successfully deployed in space. Combining gigantic sizes that don’t fit inside rocket fairings and massive amounts of fuel to relocate every time the telescope needs to look at a different star are significant strikes against the concept. However, if humanity wants to directly image an exoplanet in the habitable zone of another star, there is still no better way to do so.
Enter Dr Gregg’s idea—she proposes using metamaterials for her starshade, which is robotically constructed in orbit. Metamaterials have several advantages over existing proposed starshades (one of which, by Nobel Prize winner John Mather, is another NIAC recipient this year).
First, metamaterials are lighter. As with all things launched into space, being lighter means less cost – or, in this case, the ability to bring more fuel, allowing the starshade to operate longer than alternatives.
Second, the specific kinds of metamaterials she proposes to use are much less likely to break. As she mentioned to Fraser in an interview, “The more stiffness a material has, the less damping it has. It’s just sort of a natural trade-off”. So, if a starshade is made from traditional materials, it would either be stiff and rigid but prone to vibrational strain when moving between positions or being deployed, or it would be very flexible but would have difficulty holding its shape when it’s supposed to.
The metamaterial Dr. Gregg and her colleagues have proposed uses a type of material that both holds its structure well but also suppresses vibration by a unique use of a material called a phononic crystal. These were initially engineered to dissipate sound waves. This means that when used as a material in a starshade, it could dampen any feedback on the structure from things like micrometeoroid impacts, solar radiation, or even the process of deployment and assembly.
Using robots to deploy the starshade is another focal point of Dr. Gregg’s work, as she discusses with Fraser. Still, for this Phase I NIAC project, she is focusing on developing the model for starshade itself and selecting the appropriate material. As with all NIAC projects, she can apply for more funding in a Phase II round upon completion of her Phase I. If she receives it, humanity will be one step closer to seeing a giant floating petal in space – but one with very particular mechanical and structural properties.
Learn More:
NASA / C. Gregg – Dynamically Stable Large Space Structures via Architected Metamaterials
UT – In Order to Reveal Planets Around Another star, a Starshade Needs to Fly 40,000 km Away from a Telescope, Aligned Within Only 1 Meter
UT – Starshade Prepares To Image New Earths
UT – To Take the Best Direct Images of Exoplanets With Space Telescopes, we’re Going to Want Starshades
Lead Image:
Artist concept highlighting the novel approach proposed by the 2025 NIAC awarded selection of the Dynamically Stable Large Space Structures via Architected Metamaterials concept. NASA/Christine Gregg
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Star formation in the early Universe was a vigorous process that created gigantic stars. Called Population 3 stars, these giants were massive, extremely luminous stars, that lived short lives, many of which were ended when they exploded as primordial supernovae.
But even these early stars faced growth limitations.
Stellar feedback plays a role in modern star formation. As young stars grow, they emit powerful radiation that can disperse nearby gas they need to keep growing. This is called protostellar radiative feedback, and it takes place in addition to the restrictive effect their magnetic fields have on their growth.
However, new research shows that the growth of Pop 3 stars was limited by their magnetic fields.
The research is titled “Magnetic fields limit the mass of Population III stars even before the onset of protostellar radiation feedback.” The lead author is Piyush Sharda, an astrophysicist at the Leiden Observatory in the Netherlands. It’s available on the pre-print server arxiv.org.
Scientists observe stars forming in the modern Universe to understand how the process plays out. This is difficult because stars take so much time to form, while we’ve only been watching young stars from a great distance for a few decades. Stars are massive, energetic, complex objects that don’t give up their secrets easily.
There are many unanswered questions about star formation, but a general picture has emerged. It starts with a cloud of cold molecular hydrogen that collapses into dense cores. These cories become protostars, also called young stellar objects (YSOs). Accretion disks form around the young stars, and this is where radiative feedback comes in.
As young stars accrete mass, they heat up. They radiate this heat outward into their own accretion disks. As the material in the disk heats, it slows or even stops the accretion process. So radiative feedback limits their growth.
YSOs also rotate more rapidly than more mature stars. The rotation creates powerful magnetic fields, and these fields drive jets from the YSO’s poles. These jets steal away some of the accretion energy, limiting the stars’ growth. The jets can also disperse some of the surrounding gas, further limiting their growth.
However, the picture may look different for Pop 3 stars. To begin with, their existence is hypothetical at this point in time, though theory supports it. If they’re real, astrophysicists want to know how they formed and what their growth limits were. If they’re real, Pop 3 stars played a critical role in the Universe by forging the first metals and spreading them out into space.
According to the authors of the new research, simulations haven’t been thorough enough to explain the masses of Population 3 stars.
“The masses of Population III stars are largely unconstrained since no simulations exist that take all relevant primordial star formation physics into account,” the authors write. “We evolve the simulations until 5000 years post the formation of the first star.”
In the team’s more thorough simulations, which include magnetic fields and other factors, these early stars are limited to about 65 solar masses. “In 5000 yrs, the mass of the most massive star is 65 solar masses in the RMHD <radiation magnetohydrodynamics> simulation, compared to 120 solar masses in simulations without magnetic fields,” they write.
The results show that both simulation runs that included magnetic fields are fragmented, leading to the formation of Pop 3 star clusters. That means that the evolution of the most massive Pop 3 stars in both runs is influenced by the presence of companion stars.
The difference comes down to gravity and magnetic fields working against each other. As young stars accrete mass, their gravitational power increases. This should draw more material into the star. But magnetic fields counteract the gravity. This all happens before radiative feedback is active.
The results also show that in both simulations that include magnetic fields, the amount of mass that reaches the envelope initially increases, then declines. However, the results were different in the simulations without magnetic fields. In those simulations, mass transfer from the envelope to the accretion disk is fast at first, creating a decline in the mass in the envelope and a build-up of mass in the disk. “This mass is consequently accreted by the star at a high rate,” the authors write.
“We learn that magnetic fields limit the amount of gas infalling onto the envelope at later stages by acting against gravity, leading to mass depletion within the accretion disk,” the authors explain. “The maximum stellar mass of Population III stars is thus already limited by magnetic fields, even before accretion rates drop to allow significant protostellar radiative feedback.”
Though Population 3 stars are only hypothetical, our theories of physical cosmology rely on their existence. If they didn’t exist, then there’s something fundamental about the Universe that is beyond our grasp. However, our cosmological theories do a good job of explaining what we see around us in the Universe today. If we’re putting money on it, place your bets on Pop 3 stars being real.
“Radiation feedback has long been proposed as the primary mechanism that halts the growth of Pop III stars and sets the upper mass cutoff of the Pop III IMF (initial mass function),” the authors write in their conclusion. They show that magnetic fields can limit stellar growth before feedback mechanisms come into play.
“This work lays the first step in building a full physics-informed mass function of Population III stars,” the authors conclude.
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The structure of the cosmos is rooted in symmetry. As first demonstrated by Emmy Noether in 1918, for every physical law of conservation in the Universe, there is a corresponding physical symmetry. For example, all other things being equal, a baseball hit by a bat today will behave exactly the same as it did yesterday. This symmetry of time means that energy is conserved. Empty space is the same everywhere and in all directions. This symmetry of space means that there is conservation of linear and rotational momentum. On and on. This deep connection is now known as Noether’s Theorem, and it is central to all of modern physics.
Where Noether’s Theorem really shows its power is in particle physics. Although the mathematics of particle physics is complex, the underlying symmetries govern what can happen when particles collide. So, conservation of charge means that when a particle collision creates a shower of new particles, the total charge of all the particles must equal the total charge of the particles before the collision. Another basic symmetry is parity, also known as mirror symmetry. If you stand in front of a mirror and raise your right hand, your mirror image will raise its left. If you spin a ball toward your left, the mirror ball will spin to the right. Since elementary particles have an inherent rotation or spin, this means that particle showers should appear in rotational pairs.
One way to test the laws of physics is to see where certain symmetries are broken. In particle physics, an important symmetry is the combination of charge and parity, known as charge-parity, or CP symmetry. CP symmetry is what requires that for every matter particle, there must be a corresponding antimatter particle. For a long time, it was thought that CP symmetry was conserved, which was a problem for cosmologists since our Universe is made almost entirely of matter, not a mix of matter and antimatter. But in the last half of the 20th century, we found examples of CP violations, which led to a revolution in our understanding of the standard model of particle physics.
Although it isn’t mentioned as much, the same symmetries apply to general relativity. In fact, Einstein’s equations can be derived by applying the physical symmetries seen in Newtonian physics while dropping the requirement that space be Euclidean. Technically, the principle of equivalence Einstein used to derive relativity is a consequence of symmetries, not the other way around. So what if we used these symmetries to test relativity the way we do in particle physics? One way to do this would be to look at the mergers of black holes, which is the point of a recent study in Physical Review Letters.
In this work, the team looked at the gravitational waves generated by the mergers of stellar black holes. Specifically, they focused on the polarization of the gravitational waves. Since gravitational wave polarization is connected to the rotation of the merging black holes, this allowed the team to test parity conservation. Under the standard model of general relativity, parity should be conserved, and this is precisely what the team found. To the limits of observation, black holes don’t violate parity. That said, we should note that the observational limit is pretty weak. We simply haven’t observed enough mergers to conclusively prove black holes obey parity, though we expect that they do.
The team also looked at the recoil effect of black holes in a second paper. When two black holes merge, the resulting black hole can get a gravitational kick that sends it flying off from its point of origin. If spatial symmetry holds, then the recoil of black holes shouldn’t show any bias, such as having more of them speed away from us than toward us. Again, the team saw no violation of symmetry, in agreement with general relativity.
Neither of these results are strong enough to be conclusive, and since both results are what we expect, there’s nothing surprising in this work. But studies such as this are worth doing as we continue to gather data. We know that somehow general relativity and quantum theory must combine into a general theory of quantum gravity, and we know that quantum theory violates some of the symmetries of general relativity. A big question is whether quantum gravity violates any symmetry as well. In time, studies such as these could give us the answer.
Reference: Calderón Bustillo, Juan, et al. “Testing mirror symmetry in the Universe with LIGO-Virgo black-hole mergers.” Physical Review Letters 134.3 (2025): 031402.
Reference: Leong, Samson HW, et al. “Gravitational-wave signatures of mirror (a) symmetry in binary black hole mergers: measurability and correlation to gravitational-wave recoil.” arXiv preprint arXiv:2501.11663 (2025).
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One of my gripes with ‘The Martian’ movie was the depiction of the winds on Mars. The lower air density means that the sort of high speed winds we might experience on Earth carry far less of an impact on Mars. During its 72 flights in the Martian air, NASA’s ingenuity helicopter took meticulous records of the conditions. A new paper has been released and reports upon the wind speeds on the red planet at various altitudes. Previous models suggested wind speeds would not exceed 15 m/s but Ingeniuty saw speeds as high as 25 m/s.
Of all the planets in our Solar System, Mars is perhaps the most similar to Earth, similar but with stark differences. The weather on Mars is harsh and extreme, characterised by cold temperatures, a rarefied atmosphere and dust storms. The average temperature is around -60°C but it can reach a toasty 20°C in summer near the equator. It’s atmosphere is composed mostly of carbon dioxide and is about 100 times thinner than Earth’s so it offers little insulation or protection from solar radiation. On occasion, the winds on Mars whip up global dust storms that obscures the planet’s surface from view.
Our model of the Martian atmosphere was believed to be fairly accurate, that is until Ingenuity arrived and completed more than 70 successful flights. As part of the Mars 2020 mission and the first aerial vehicle to successfully complete powered flight on another world, Ingenuity revealed some surprising conditions. Surprisingly too perhaps, the first attempt at powered flight was supposed to be a technology demonstration but instead, it provided high resolution images to help direct the ground based rover and collected data from the atmosphere and became a key part of Mars 2020.
One of the outcomes from Ingenuity’s flights was a better understanding of Martian winds. In a paper written by Brian Jackson and team in the Planetary Society Journal, the team explained their rather ingenious approach. Knowing that the payload was severely limited on board, the decision was taken to use Ingenuity itself to confirm windspeeds. Previous studies had shown that the tilt of a stably hovering drone can be used to calculate speeds. Drones produce forward thrust by tilting in the direction they need to move, if they are stable and in a hover yet the wind is blowing, the drone will drift. Instead and to counteract the drift, the drone tilts flying into wind to maintain position relative to the ground, tilting more in a stronger headwind.
Measuring the tilt is relatively straightforward thanks to a collection of engineering sensors, cameras and accelerometers. With all of the information gathered by these onboard pieces of equipment and returned to Earth, the analysis and calculation of the drone at different altitudes has enabled the wind speeds to be accurately calculated.
The results were a surprise, showing that the winds on Mars were generally higher than anticipated. Speeds were measured at altitudes from 3 to 24 metres and were found to be blowing at anything up to 25 m/s. This perhaps is a result of Ingenuity’s unique capability of being able to measure speeds at different altitudes over a period of time. Previous measurements have been achieved from probes as they have descent through the atmosphere or from probes on the ground. Taking the success of Ingenuity forward, mission specialists working upon the Dragonfly rotorcraft that will be visiting Titan hope to be able to replicate the results and gain a better understanding of its wind profile too.
Source : Profiling Near-surface Winds on Mars Using Attitude Data from Mars 2020 Ingenuity
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