Planets that get too close to their host stars are liable to be engulfed and consumed. New research explores how to identify stars that have had a planetary snack.

It’s Snack Time

Being a planet that closely orbits its star is dangerous, and various dynamical processes can draw a planet inward past the point of no return. When a planet vanishes beneath the surface of its host, it eventually disintegrates within the star, its atoms mixing into the blazing stellar soup.

This outcome is likely extremely common across the universe, and researchers have begun to see evidence for it: stars that appear to have absorbed angular momentum from their planets, white dwarfs with uncanny metals in their spectra, and stars with chemical abundances that don’t match those of their siblings. Now, in a recent publication led by Kaitlyn Lane (Vanderbilt University), researchers seek to find observational signatures of planetary engulfment of rocky exoplanets by main-sequence stars.

Modeling Engulfment

Lane’s team focused on main-sequence stars in the range of 0.5 to 1.4 solar masses, using one-dimensional analytical models to determine which of these stars will most readily display signs of having engulfed a planet. They simulated the stars as they consumed either an Earth-like planet or a super-Earth with the same composition as Earth but 15 times its mass.

At the onset of the model, the engulfment is set to begin, the planet placed tangent to the star’s surface. The planets sink down and orbit just barely within their stars for 1–10 years, their solid surfaces slowly beginning to evaporate.

After that relatively lengthy phase, the process proceeds rapidly: as the planet inches deeper into its star, the drag forces grow stronger and the planet’s demise accelerates, with the planet disintegrating over the course of hours. In the last phase, the planet makes its final plunge and is destroyed in a half hour.

Signs of Planets Past

Lane’s team found that the planets tended to be destroyed fully within the outer convective layer of their stars, except in the case of the most massive stars studied here. For more massive stars, the outer convective zone is shallower than it is for the less massive stars, allowing a chunk of each planet to survive the passage through the convective zone to reach the radiative zone below.

What this translates to, for the purposes of identifying planet-eating stars from afar, is that stars near the top of the mass range studied — from 1.0 to 1.4 solar masses — make the best targets. This is because the tell-tale planetary metals are not overly diluted within the stars’ relatively small convective zones, making these elements easier to detect. In terms of specific metals, the authors found that aluminum, calcium, and vanadium are the best signposts of planetary engulfment, with lithium also making the list.

While the authors acknowledge that there’s more work to be done — they plan to investigate the impacts of planetary engulfment on stellar structure more closely, for example — this work represents an important foray into identifying targets for future studies of stars that have eaten their planets.

Citation

“Observable Metal Pollution in Main-Sequence Stars: Simulations of Rocky Planets Engulfed by Stars in the 0.5 to 1.4 M_⊙ Range,” Kaitlyn T. Lane et al 2026 ApJ 1003 67. doi:10.3847/1538-4357/ae5b9a

The post Now That’s Metal: How to Spot Stars That Have Swallowed Their Planets appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: A Panchromatic JWST Spectrum of a Giant Starspot on the Fully Convective M Dwarf TOI-3884
Authors: C. A. Murray et al.
First Author’s Institution: University of Colorado Boulder
Status: Published in ApJ

We often picture stars as smooth, glowing spheres, as if they’ve been run through an Instagram filter. But real stars have spots: cooler, darker regions on a star’s surface caused by strong magnetic fields.

Annoyingly, these spots can seriously interfere with how we study exoplanet atmospheres.

How to Probe a Planetary Atmosphere

Planetary atmospheres are often probed through transmission spectroscopy. When a planet transits its star, some starlight passes through the planet’s atmosphere before reaching us. We can distinguish the light that has passed through the planet’s atmosphere by comparing the star’s light in transit versus out of transit. In doing so, we can isolate the atmospheric spectrum and look for absorption features of species like water or oxygen.

Easy, right?

How Starspots Get in the Way

Things get more complicated once we stop thinking of the star as if it’s been smoothed out by an Instagram filter. Starspots are cooler than the surrounding stellar surface, which means they emit a different spectrum. They are also constantly changing: new spots can form, old ones can disappear, and the star’s rotation carries them in and out of view. This changes things.

First of all, your star’s spectrum changes over time, which could mean that the star’s spectrum out of transit is not the same as the star’s spectrum during transit. On the other hand, the planet may transit across a starspot instead of a “normal” stellar region. In this case, the light we measure during the transit is affected by the spot, and it is no longer accurate to directly compare it with the overall stellar light outside the transit.

Ultimately, absorption features that we thought were from the planetary atmosphere could actually be coming from starspot contamination instead.

Starspot Models: Our Solution?

To deal with this, astronomers build starspot models, where they vary the spots in terms of the following:

• The surface covering fraction: this parameter tells us how much of the stellar surface is covered in spots
• The temperature contrast: this parameter tells us how much cooler (in ratio) the spot is compared to the rest of the stellar surface, and by proxy how much dimmer

These models are promising, but how do we know that we have chosen the right parameters?

A Unique Laboratory: TOI-3884

The TOI-3884 system is a unique laboratory for testing our starspot models. As seen in Figure 1, it has very convenient starspot geometry, with a large starspot located close to its pole. On top of that, we observe this star almost completely pole-on, which means that we always see this starspot, no matter how much the star rotates. To top this all off, the star hosts a close-in planet, which orbits the star from pole to pole.

The planet transits the star, and as it does so, it always passes over the polar starspot. This gives us a rare opportunity to probe the spectrum of a starspot. Similar to how we can use normal in/out of transit observations to probe a planetary atmosphere, we can now compare the observations during/after a “starspot transit” to probe the starspot region. Today’s authors do exactly this using six different transit observations from JWST.

So… How Good Are Our Models?

From the JWST observations, the authors extract a starspot spectrum for the first time. Figure 2 shows this as the spot contrast (how much dimmer the spot is than the surrounding stellar surface) plotted across different wavelengths. To see how well our models are doing, they compare this observed spectrum to two commonly used starspot models. The difference between the data and the models (the residual) is plotted in the lower panel.

At wavelengths longer than about 1 micron, in the near-infrared regime, things look good! The residuals stay small, meaning the models do a solid job reproducing the observations. But move left into shorter wavelengths, in the optical regime, and the agreement quickly falls apart. The residuals grow, and it becomes clear that the models are missing something.

There’s still work to be done before we can confidently probe planetary atmospheres at optical wavelengths without worrying about stellar contamination, and this observed starspot spectrum provides a unique benchmark to test future starspot models. For now, the near-infrared remains a safer and more reliable window for planet atmosphere studies.

Original astrobite edited by Natalie Price.

About the author, Elise Koo:

I’m a PhD student at the University of Amsterdam, working to detect magnetic interactions between stars and their planets using radio and spectroscopic observations. Outside of research, I like to try out a variety of sports.

The post The First Starspot Spectrum Revealed by JWST appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Retrieving the Red Edge on Earth-Like Planets with Heterogeneous Clouds and Surfaces
Authors: Zachary Burr et al.
First Author’s Institution: Jet Propulsion Laboratory; ETH Zurich
Status: Published in ApJ

In the next 25 years, astronomers could find signs of life on other planets with the launch of the Habitable Worlds Observatory. Atmospheric signs of life, known as atmospheric biosignatures, are how astronomers currently search for life on other planets. Figure 1 shows examples of atmospheric biosignatures with pictures of each chemical’s origin on Earth. Before E.T. can phone home, though, we have to understand what chemicals make up a planet’s atmosphere. To do this, astronomers can use spectroscopy to observe a planet’s atmosphere in different wavelengths and measure the types and quantities of chemicals present.

There are many ways to observe the spectrum of a planet, but the one you’re probably most familiar with is transmission spectroscopy. You can learn more about transmission spectroscopy of exoplanet atmospheres and how to model transmission spectra with these bites: 1, 2, 3. However, all of the current techniques for exoplanet spectroscopy (including transmission spectroscopy) measure the star’s light and how the planet affects the star’s light. This means it’s heavily dependent on how we model the star’s light to indirectly observe the planet’s light. The only way to take the spectrum of a planet directly is with direct imaging: the technique that the future Habitable Worlds Observatory will use to find signs of life in planetary spectra.

But are atmospheric biosignatures the only way to tell if life exists on other planets? Short answer: absolutely not. Let’s take Earth as an example. If we imagine Earth as a directly imaged exoplanet and take spectra of the light it reflects, you’ll find that around near-infrared wavelengths (~700 nanometers or just past the red part of the visible light spectrum), the light reflected off of Earth increases sharply. This sharp increase is called the vegetation red edge and is caused by plant and ocean life on Earth’s surface as shown in Figure 2. This is made possible because chlorophyll (the thing that makes plants green) absorbs nearly all visible light but reflects near-infrared light. The vegetation red edge is an example of a surface biosignature. In today’s article, the authors determine if the vegetation red edge will be visible in spectra of Earth-like exoplanets!

Snapshots

Planets rotate; that’s how we have morning, noon, and night in 24 hours guaranteed. This means that different parts of the surface will be visible at different times when we take spectra. Sometimes, we may see more ocean than land, other times not. To determine if the vegetation red edge would be visible at all points in Earth’s day, the authors simulated nine different spectra of modern-day Earth representing nine snapshots of Earth’s rotation. Additionally, they also simulated a time-averaged spectrum that shows an entire Earth day in one snapshot without the time variability. These spectra are shown in Figure 3.

The authors then run retrieval models on all nine spectra to see if the vegetation red edge would be detectable in each spectrum, including the time-averaged one. Retrieval models take into account characteristics of the planet that would affect how light moves through its atmosphere, such as the atmospheric chemicals present and the surface gravity. They then use this information to generate possible spectral models that could fit the data. The best-fit model allows astronomers to infer what the atmosphere is made of and properties of the planet such as surface gravity. Because we are looking at Earth in visible light, much of the light from the planet is reflected. Typically, models of Earth-like planets in visible wavelengths only include atmospheric albedo: the measure of how reflective a planet’s atmosphere is. However, surface biosignatures can also be reflective as shown by the vegetation red edge. The authors use this to their advantage and introduce a surface albedo into their model that changes with the amount of desert, vegetation, and ocean visible on Earth’s surface at that time. They then further divide the nine spectra into three different types based upon the visible surface: majority land; 50% land, 50% ocean; and majority ocean. Check out the article online to see a cool animation of the Earth rotating and how the spectrum looks different at each time!

Arr! There Be… Vegetables?

After running the models, the authors were able to detect a sharp increase in the surface albedo value in every spectrum, including the time-averaged one. This result is shown in Figure 4. The authors take this result one step further in order to validate that the vegetation red edge is actually a result of surface variation of vegetation. They re-run models on each of their spectra but instead include a constant surface albedo instead of a time-varying one. This resulted in incorrectly measured radii, chemicals, and surface gravity in nearly all of the models. Without the vegetation red edge and surface features, the models could not accurately determine if life was present on Earth.

For the first time (to the author’s knowledge), the vegetation red edge has been shown to be a promising and observable biosignature in Earth-like atmospheres. This study has also laid the groundwork for future work on other surface biosignatures and their potential impact on spectra of habitable planets. Confirming signs of life in multiple different ways, both on the surface and in the atmosphere, will finally allow astronomers to say we are not alone in the universe. In fact, life likes to live on the (red) edge!

Original astrobite edited by Madison VanWyngarden.

About the author, Kaz Gary:

I am a fourth-year PhD candidate at The Ohio State University with a passion for planets. My current work focuses on modeling exoplanet observations for the Habitable Worlds Observatory and understanding planetary atmospheres. Outside of research, I help develop planetarium shows and love all forms of science communication. In my free time, I enjoy playing tabletop RPGs, painting, watching terrible reality TV, and hanging out with my pet hedgehog.

The post Life on the (Red) Edge appeared first on AAS Nova.

Each Jupiter-size planet in the galaxy falls into one of three distinct categories: hot, warm, or cold. A new study suggests that despite the apparent differences between these populations, they may have all formed from the same underlying dynamical process: a game of pool played at planetary scales.

A Diversity of Jupiters

Though our solar system has only one Jupiter-size planet, elsewhere in the galaxy we have found three different species of these massive gas giants. Cold Jupiters closely resemble their namesake and orbit far from their host stars; hot Jupiters are the opposite and are found whipping around their stars on extremely close-in orbits. In between these are the warm Jupiters, which tend to orbit in the intermediate space between 0.1 and 1.0 au.

Though these three populations are defined by their orbital distances, they differ from each other in other ways as well. For example, hot Jupiters almost never have nearby companions; if there are any other planets circling the same star, they’re usually far-out cold Jupiters. They can also orbit in pretty much any direction, including opposite the direction of their star’s spin, and are usually on perfectly circular orbits. In contrast, warm Jupiters often have friends nearby, are much more aligned with their stars’ spins, and can have modest eccentricities.

Given these differences, it’s often thought that each of these populations arrived at its current location through different dynamical processes and that the history of the warm Jupiters is likely quite different from the history of the hot Jupiters. However, a new study led by Julia Esposito (Georgia Institute of Technology) has proposed an alternative view. Maybe these populations, though they appear different now, were all created by the same process: planet–planet scattering.

Virtual Planetary Billiards

Esposito and collaborators set up 1,500 virtual planetary systems with three massive planets each, then simulated how the orbits evolved before probing the final configurations. In crucial contrast to previous simulation studies, the team initialized their Jupiters across a range of different distances and included the effects of tides sapping energy from orbits of planets that got too close to their host stars.

At the end of the simulation, the team surveyed the digital carnage. Almost every virtual system ended with only two planets after either ejecting one away from the star or having two planets collide. But, remarkably, the remaining two-planet systems looked tantalizingly similar to what we actually observe, with a mix of hot, warm, and cold Jupiters. Even more exciting, the end populations were highly correlated to where the violent scattering event took place.

For example, the warm Jupiters were almost all produced by “warm scattering” simulations, where the scattering took place between 0.1 and 1.0 au. The planets that survived the simulations and ended up as warm Jupiters matched all of the properties of the real warm Jupiter population: they had nearby companions, were moderately eccentric, and were mostly aligned with their stars. The hot Jupiters, meanwhile, were almost all produced by “cold scattering” events where the flybys happened far from the star and resulted in one planet hurtling inwards. These also matched all of the observed properties of real hot Jupiters.

The researchers concluded that planet–planet scattering can produce both the warm and hot Jupiter populations so long as you let the planets scatter from a variety of different distances. This exciting theoretical insight, if correct, would mean that astronomers could stop searching for different pathways to create each population. Happily, this model also provides testable predictions, and the authors lay out how the theory could be supported or disproven with additional data. Through virtual experiments like these, astronomers continue to build up an understanding of how the wide range of planetary architectures observed across the galaxy came to be.

Citation

“Unified Formation Channel of Hot and Warm Jupiters via Planet–Planet Scattering,” Julia Esposito et al 2026 ApJL 1003 L3. doi:10.3847/2041-8213/ae61b0

The post Playing Pool with Planets appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: A Deep Search for Exomoons Around WISE 0855 with JWST
Authors: Mikayla J. Wilson et al.
First Author’s Institution: University of California, Santa Cruz
Status: Published in AJ

The “Moon”-umental Question

The solar system hosts hundreds of moons, ranging from volcanic worlds like Io around Jupiter, to icy objects like Enceladus around Saturn, to captured objects like Neptune’s retrograde moon Triton. Moons are essential to our model of how the solar system formed and also offer some of the best chances we have for finding life beyond Earth.

Astronomers also expect exomoons, or moons orbiting planets outside the solar system, to be abundant around other giant exoplanets. But how common are exomoons? How do they compare to the moons in our solar system?

In order to begin answering those questions, we must first detect an exomoon, which has proved difficult despite decades of searching by astronomers. Fortunately, JWST presents a new opportunity to uncover the exomoon population by looking at lonely free-floating planets as they drift through space.

Why Free-Floating Planets?

One proposed method for searching for exomoons is by looking for their transits in front of their host planets, characterized by the dips in brightness of the planet as the moon passes in front, blocking the planet’s light. Looking for exomoon transits around planets orbiting stars is quite difficult, as the bright starlight can easily drown out the small signals of exomoon transits. Free-floating planets solve this issue by removing the star entirely, increasing our sensitivity to such detections. (See this bite for a good review.)

The authors of today’s article directed the exomoon hunt towards the free-floating WISE J085510.83-071442.5 (or WISE 0855). It has the prestige of being the coldest known brown dwarf (250–285K) while also sitting at a relatively low mass (3–10 Jupiter masses). Notably, it is also one of our closest neighbors at a distance of only 7.4 light-years, making it ideal for high-precision observations despite its faintness. Even though brown dwarfs are technically distinct from planets, the authors opt to refer to companions around WISE 0855 as moons given WISE 0855’s “planetary-mass” status. (It’s complicated…)

Repurposing JWST Data… for Moons!

The JWST observations used in this study contain 11 hours of near-infrared (2.87–5.27 microns) time-series spectra originally intended to study water clouds and weather on WISE 0855. Time-series brightness monitoring can also be used for transit searches, which the authors take advantage of.

One complication is that WISE 0855 is variable, meaning its intrinsic brightness changes over time. Variability is likely driven by clouds and other dynamic processes within its atmosphere. So how do the authors distinguish between a passing moon and a turbulent atmosphere? The key idea is that variability is wavelength dependent, meaning that the brightness of WISE 0855 will fluctuate differently depending on the observed wavelength. In contrast, transits are “gray,” meaning that the same amount of light is blocked at all wavelengths, producing a consistent feature across the entire spectrum.

Finding Moons with Statistics!

The authors apply this idea and pick out two wavelength regions of WISE 0855’s spectrum that contain two distinct variability patterns, which should both contain an identical moon transit signal (if present). They then generate a light curve (how brightness changes over time) for these two regions (see Fig. 1).

To appropriately model the variability, the authors employ Gaussian processes, a flexible tool that can model complex, quasi-periodic signals like atmospheric variability. They compare fits from two types of models:

• Gaussian processes–only model: Assumes that all observed variability is intrinsic to the planet itself
• Gaussian processes + transit model: Includes a simple trapezoidal exomoon transit signal that is simultaneously fit in both light curves

Using Bayesian evidence (a measure of how well each model explains the data), they determined which model was favored. So, what do they find?

The Bad News and the Good News

Based on Bayesian evidence, the authors conclude that there are no statistically significant detections of exomoons in the data. The results suggest very weak evidence for a ~0.53-Earth-radius moon at a wide separation from WISE 0855 — an unlikely scenario given that transit probability decreases at greater separations (and therefore longer orbital periods).

Yet, the study goes further: What kinds of moons is JWST able to detect, if any? To answer this, the authors performed injection and recovery tests, where they injected artificial transit signals of varying depths (exomoon sizes) into the data and tested how well their models were able to recover them (results shown in Fig. 2). They find that JWST is capable of detecting 96% of transits with depths ≥0.5%, equivalent to a Titan-like moon. Smaller Io-like moons were also detectable more than half of the time. This means that if a Titan analog had actually transited during these observations, we would almost certainly have seen it!

JWST will continue to gather more time-series data of free-floating planets, brown dwarfs, and directly imaged exoplanets, each providing a new opportunity to help us better understand the moon population outside of our solar system. We’re still waiting for the first confirmed exomoon, but when that transit finally happens, we know that JWST will be ready.

Original astrobite edited by Kelsie Taylor.

About the author, Jared Bull:

I am a 2nd-year PhD student at Johns Hopkins University. I study brown dwarf variability and am interested in using time-series observations to uncover dynamic processes within their atmospheres. In my free time I like to read, cook, and do astrophotography.

The post Hunting for Exomoons Around a Lonely Planet appeared first on AAS Nova.

Orbiting a white dwarf, the exoplanet WD 0806b is the subject of a recent study using JWST to measure the atmospheric conditions governing the planet.

Directly Imaged Exoplanet WD 0806b

Most of the 6,000 and counting exoplanets discovered thus far have been detected due to their impacts on their host star — passing in front of the star and causing it to dim, or gravitationally tugging on the star and causing it to wobble. On rare occasions, though, astronomers have been able to catch the exoplanet itself through direct imaging. Directly imaged exoplanets offer key insights that cannot be obtained through indirect detection methods. Luminosity measurements and spectral emission features allow astronomers to more directly measure planet mass, radius, and composition otherwise inferred from the host star.

Included in the about 90 distant planets that have posed for a picture is WD 0806b, a rare exoplanet companion trotting around a white dwarf at an orbital distance of 2,500 au (50 times the distance from the Sun to the Kuiper belt!). Originally discovered with the Spitzer Infrared Array Camera in 2011, WD 0806b is the second-coldest directly imaged exoplanet to date. With JWST’s high-precision photometric and spectroscopic capabilities, WD 0806b provides a unique opportunity to probe the atmospheric chemistry of cold giant planets and take steps toward understanding the co-evolution of white dwarfs and their surviving exoplanets.

WD 0806b’s Atmospheric Abundances from JWST

Aiming to characterize the physical properties and atmospheric composition of WD 0806b, Ben W.P. Lew (Bay Area Environmental Research Institute; NASA Ames Research Center) and collaborators used JWST’s Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec) to obtain high-resolution imaging and spectroscopy of the exoplanet. Combining these observations, prior lower-resolution observations, and evolutionary planet models, the authors estimated the physical properties of WD 0806b including mass, radius, surface gravity, and effective temperature.

From the derived physical properties, the authors modeled the NIRSpec spectrum to estimate molecular abundances and elemental abundance ratios in the atmosphere of WD 0806b. They obtained measurements of multiple molecules including carbon dioxide, carbon monoxide, and ammonia; these molecular abundances offer the opportunity to test chemical equilibrium and disequilibrium as well as eddy diffusion, or bulk mixing, in the planet’s atmosphere. The authors developed a novel chemical analysis framework to determine how bulk mixing varies with altitude in WD 0806b and reported the first observational evidence that mixing becomes weaker at higher altitudes in exoplanet atmospheres. This result points to the need for future studies exploring the impact of these chemical processes on spectra and photometry, which are essential to characterizing cold giant planets.

This study highlights how high-precision JWST data can reveal a rich collection of atmospheric conditions, chemical composition, and physical processes occurring in cold giant planets. With such a wide orbit from its host white dwarf, WD 0806b serves as an interesting case study for how giant planet composition may reflect the formation and evolutionary history of the overall system. Future observations of and comparisons to similarly cold giant planets will further uncover how atmospheric characterization may fit into our understanding of exoplanets and their histories.

Citation

“JWST Spectral Retrieval of Cold Directly Imaged Planet WD 0806b and the First Measurement of Altitude-dependent K_zz in Exoplanet Atmospheres,” Ben W.P. Lew et al 2026 AJ 171 227. doi:10.3847/1538-3881/ae4747

The post Characterizing the Atmosphere of Exoplanet WD 0806b with JWST appeared first on AAS Nova.

After AAS 247 in Phoenix, Arizona, AAS Nova Editor Kerry Hensley and I had the chance to travel about 150 miles south for a tour of Kitt Peak National Observatory.

A Window into Kitt Peak

Located 60 miles southwest of Tucson, Kitt Peak National Observatory (KPNO) resides on a mountain top within the Tohono O’odham Nation reservation. Founded in 1958, Kitt Peak is home to nearly two dozen active telescopes ranging in wavelength coverage and scientific objectives. Ronald Proctor, Lori Allen, and Jacelle Ramon-Sauberan, all serving in crucial roles for the observatory, led our tour around the mountain.

Our visit began in the new Windows on the Universe Center — the first science center inside of a telescope. Situated inside the retired McMath-Pierce Solar Telescope, the Windows Center takes visitors through exhibits exploring the universe, the telescope’s original control room, and the observatory’s connection to the Tohono O’odham Nation.

The center’s lobby introduced visitors to the beautiful land KPNO calls home. Working with Tohono O’odham linguists, Jacelle, the observatory’s Tohono O’odham Nation Education Liaison, curated the lobby exhibit that features the native language and the Nation’s connection to astronomy and the observatory. The science center serves as an educational resource and place of cultural exchange, expanding the relationship between the observatory and the Tohono O’odham Nation. 

After walking through an introduction to the universe exhibit, visitors enter the original control room of the telescope. Mirrors across the room’s ceiling focus the Sun’s light onto table screens where visitors can observe the Sun in real time without burning their eyeballs. In addition to observing the Sun, the solar telescope allowed astronauts in the 1960s to view a projection of the Moon’s surface and plan their landing site for the Apollo 11 mission. Visitors can stand in the same place and witness the instruments that made the moon landing possible.

At the end of the Windows Center is a Science On a Sphere Theater — a spherical display system that allows visitors to see planets, stars, moons, and even large-scale structures of the universe in 3D. Featuring multiple programs, the theater takes visitors through the universe and displays data collected right there on the mountain!

A WIYN for Exoplanetary Science

Though not typically open to the public for tours, our next stop took us to the WIYN 3.5-meter telescope. This telescope is operated and owned by the WIYN Consortium, a partnership between the University of Wisconsin, Indiana University, NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory; formerly NOAO), Pennsylvania State University, and Princeton University. Operating since 1994 with a strong collection of instruments, WIYN has observed galaxies near and far, stars across their lifetimes, and exoplanets tugging on their host stars.

WIYN’s newest instrument, NEID (pronounced “NOO-id”), has been advancing exoplanetary science since its first light in early 2020. Derived from the word meaning “to see” in the Tohono O’odham language, NEID is a high-resolution spectrograph that uses the radial velocity method to detect exoplanets. As a planet orbits its host star, its gravitational pull induces a wobble in the star, and NEID can detect these wobbles with unprecedented precision. This instrument allows astronomers to find exoplanets that were previously undetectable.

The partnership between public and private universities and a government institution was the first of its kind. Through this consortium, hundreds of undergraduate and graduate students have conducted research with WIYN, and the telescope’s suite of instruments have enabled early career astronomers to explore the universe both near and far.

Mysteries of Dark Energy at Mayall

We concluded our tour at the Mayall 4-meter Telescope, the tallest telescope dome on the mountain at a staggering 18 stories high. This iconic telescope saw first light in 1973, and at the time, was the second-largest (in diameter) telescope in the world. Originally built for wide-field optical and infrared studies of the universe, the Mayall has enabled decades of critical scientific research.

Mayall is now home to the Dark Energy Spectroscopic Instrument (DESI), the most powerful multi-object survey spectrograph in the world. The DESI survey measures the impact of dark energy on the expansion of the universe through creating the largest ever 3D map of the universe. Mapping the distances to hundreds of millions of galaxies, DESI has revolutionized cosmology and enabled groundbreaking research into the origins of the universe. 

From the telescope’s massive dome, to the busy DESI control room, to the gallery floor with a nearly 360 degree view of the surrounding desert, the Mayall offers visitors a unique glimpse into Kitt Peak’s history and its future. While WIYN is a hidden gem, the Mayall 4-meter Telescope is open to the public for tours daily, so you can experience the exciting era of research and discovery at KPNO. 

Visit Kitt Peak

Interested in getting a peek yourself? KPNO is open to the public daily with multiple tour types to choose from, including both daytime and nighttime visits! Plan your visit to Kitt Peak here.

The post Getting a Peek of Kitt Peak National Observatory appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Soot Planets Instead of Water Worlds
Authors: Jie Li et al.
First Author’s Institution: University of Michigan
Status: Published in ApJL

They Might Be Planets with a Lot of Water…

Since the discovery of PSR B1257+12 c and d in 1992 and  51 Pegasi b in 1995, we have found evidence for thousands of planets in other star systems. One of the most striking things (aside from how common planets seem to be) is how many of them are so unlike anything we had imagined we would find. Our growing list of exoplanets includes a truly remarkable variety of types, from cold rocky planets smaller than Earth to scorching hot giants bigger than Jupiter.

However, one category of planets is particularly interesting: the sub-Neptunes. These planets, smaller than Neptune but larger than Earth, are characterized by their low densities, which suggests they could be dominated by water or volatile-rich atmospheres. What makes sub-Neptunes so intriguing is that we don’t have a clear counterpart for them in our own solar system. As such, we don’t really know a lot about them other than there seem to be a lot of them out there.

Although these planets are sometimes theorised to be rocky worlds with large hydrogen–helium envelopes, they have alternatively been considered as water worlds, i.e., worlds with giant planet-wide oceans thousands of kilometres deep. The thinking goes that since water ice appears to be abundant beyond the snow line, water worlds would be a natural consequence of planet formation. And if these planets exist, some might host a temperate liquid ocean with the conditions for life.

…or They May Just Be CHON(ky)

However, today’s article suggests that these supposed water worlds may not be as wet as we think they are. They may instead be rich in what are called refractory carbonaceous materials. This term describes solids rich in carbon, hydrogen, oxygen, and nitrogen, or CHON. It is a bit of a mouthful and is often just referred to as “soot,” but it is important to remember that it is different from the black stuff you would find in ye old chimney. Soot, in this case, is a major component of comets. We know that this type of material is present around planet formation, as protoplanetary dust contains not just silicates (rock) and water ice but also a significant amount of CHON, and comets are leftovers from this dust.

Soot is stable and remains in the solid state to much greater temperatures (∼500K) than water ice (∼160K), so the authors argue that there should be regions in the protoplanetary disk where planets accrete both rock and soot but little water. They define a “soot line” akin to the snow line and look at three archetypical planets that may form, shown in Figure 1.

Inside the soot line, planets would be rock-rich worlds with low carbon or water content (e.g., terrestrial planets) because it is just too hot for any soot to stay together. Beyond the soot line but before the snow line, you would find carbon-rich rocky worlds (soot planets). They have low water content, as it is still too hot for water ice to exist, but these planets are rich in CHON. Beyond the snow line, a combination of rock/carbon/water worlds becomes possible, here labelled as soot-water worlds. The authors note that even though the last one has a significant fraction of water, it is distinct from traditional “water worlds” because it includes a significant component of hydrocarbon-rich material. Again, it is also important to remember that a soot world wouldn’t mean a black powder ball hanging in space, but rather a world that is composed of a lot of CHON, like Saturn’s moon Titan.

What Do the Models Say?

The authors got down to modelling planet compositions based on both observations of protoplanetary disks and the distribution of solid materials found in comets.

They considered two model planets. One is fully stratified, i.e., with a metallic core enclosed in a silicate mantle overlain by a hydrocarbon-rich layer and then a water-ice surface layer. The other, a single-layer mixed planet, is a hypothesised scenario where iron, silicate, soot, and water are fully mixed throughout the planet as a result of exotic chemistry from the high temperature inside the sub-Neptune planet. They expect any potential real planets to lie somewhere between the two extremes. The mass–radius relations for these models can be seen in Figure 2, where they are also compared to a number of known exoplanets, of which several fall within the models’ parameter spaces.

A particularly interesting result that the authors note is that the predicted mass–radius relationship for the water worlds, which incorporates soot, is similar to that predicted previously for a 50% water planet with no carbon. That is, if you base your interpretation on the mass–radius relationship alone, it is impossible to distinguish between a world made of rock and water and a water-rich planet that incorporates a significant amount of soot.

We Might Have a Telescope That Can Help

How might we break through this impasse? Well, because significant fractions of methane and other simple hydrocarbons are expected to be released from the interior, the soot-rich planets may feature methane-rich atmospheres. These may naturally lead to the formation of hydrocarbon hazes, akin to the tholins in Titan’s atmosphere.

Looking at the atmospheres of exoplanets is one of the main mission goals of JWST. Many of the spectra from sub-Neptunes have so far been featureless, which may indicate the presence of clouds or photochemical haze. The telescope also has the ability to detect carbon-bearing species in the atmospheres of other sub-Neptunes, like with the discovery of CO₂ and CH₄ in the atmospheres of K2-18b and TOI-270d. Although these planets currently orbit interior to the soot lines of their respective stars, they may have originally formed farther out and later migrated inward during their evolution. Of particular interest is TOI-270d. Aside from also showing signs of water, it has a carbon-to-oxygen ratio that is moderately high for the planet, hinting that it could be a world with a considerable amount of soot.

The presence of soot may have significant implications when it comes to habitability. The planet’s core may be rich in diamond, which would impede the movement of volatiles in the mantle. This would make it challenging for the planet to generate a magnetic field and thus leaving any potential life vulnerable to cosmic radiation. However, they could also be abundant in methane and other volatile organic compounds, substances thought to be crucial for the development of prebiotic chemistry. Regardless, it is interesting that there might be something out there that is not so unlike something we know from our own solar system, a hazy supersized Titan. While the frigid moon is unlikely to show signs of life, a temperate soot-water world might be one place to look in the future.

Original astrobite edited by Sowkhya Shanbhog.

About the author, Kasper Zoellner:

I have a Master of Science in astronomy and I am currently working towards a PhD in physics and educational science. My greatest passion is the search for exoplanets and how stellar variability may influence the possibility of life. I am also interested in science outreach, education and discussing what sci-fi novel to read next!

The post Are Water Worlds Just Made of Soot? appeared first on AAS Nova.

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

Earth Detecting Earth: At What Distance Could Earth’s Constellation of Technosignatures Be Detected with Present-day Technology?

Published February 2025

Main takeaway:

In a collaborative effort between the Search for Extraterrestrial Intelligence (SETI) Institute and the Penn State Extraterrestrial Intelligence Center, Sofia Sheikh (SETI Institute) and team turned inward to expand the search for intelligent life in the universe. Right here on Earth, humans have created a laboratory of technological signatures that can be detected from space — if another Earth-like civilization is out there, could they detect us? Using theoretical modeling, the authors determined the reaches of various human technosignatures such as radio transmissions, optical and infrared emission, satellites, and other probes sent into space. They found humanity’s strongest signals, radio transmissions, could be detected as far as 12,000 light-years away.

Why it’s interesting:

Scientists search for intelligent civilizations by hunting for signs of technology — signals or patterns that natural phenomena cannot explain. While we cannot expect other intelligent life to look exactly like Earth’s, many SETI projects have surveyed the skies for hypothetical signals far exceeding humanity’s own technological advancements. Taking a step back, Sheikh and collaborators considered where human technology is currently and what present-day instrumentation could pick up on if we were to search for ourselves. This “Earth detecting Earth” paradigm recenters the search for intelligent life and provides a multiwavelength framework for understanding the detectability of technology on far-away worlds.

Earth’s constellation of technosignatures:

What exactly are Earth’s many technosignatures, and how far could our current technology detect them? The most prominent and farthest detectable signal comes from radio transmissions. As the authors noted, these signals come from multiple sources: targeted radar transmissions used to characterize planets and asteroids, radio transmissions used to communicate between space probes and ground stations (e.g., space telescopes, Mars rovers, etc.), and radio leakage from Earth’s communication systems like cell towers and broadcasting stations. Additionally, there are atmospheric technosignatures from air-polluting compounds, optical and infrared emission from cities, targeted lasers from telescopes, and interplanetary and interstellar probes sent into space. All of these combined create a constellation of technosignatures detectable across a range of distances from Earth. This study underscores the importance of assessing Earth’s technology and detection capabilities, and repeating this type of study as technological advancements continue will enhance the search for intelligent life.

Citation

Sofia Z. Sheikh et al 2025 AJ 169 118. doi:10.3847/1538-3881/ada3c7

The post Selections from 2025: Could Earth Detect Earth? appeared first on AAS Nova.

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e

Published September 2025

Main takeaway:

Ana Glidden (Massachusetts Institute of Technology) and collaborators used JWST to collect transmission spectra of the exoplanet TRAPPIST-1e. The team found evidence of stellar contamination in all of their observations, and they found that the data didn’t lean strongly in favor or against the planet having an atmosphere. Venus-like or Mars-like atmospheres were disfavored, hydrogen-rich atmospheres with traces of methane and carbon dioxide were excluded, and nitrogen-rich atmospheres with traces of methane and carbon dioxide were permitted.

Why it’s interesting:

TRAPPIST-1e is one of seven confirmed planets orbiting TRAPPIST-1, a cool M-dwarf star that is just larger than Jupiter and only 41 light-years away. All of these planets are roughly the size and mass of Earth, and as many as four of them — planets d through h — are thought to lie within the tiny star’s habitable zone. Thus, this system offers an excellent opportunity for powerful observatories like JWST to characterize the atmospheres of several potentially habitable planets. This study by Glidden’s team presents JWST’s first look at TRAPPIST-1e’s atmosphere through transmission spectroscopy.

How TRAPPIST-1 complicated the observations:

When examining an exoplanet that closely orbits its host star, special care must be taken to separate the signals from the planet and the star. This is especially tricky for active stars like TRAPPIST-1, whose surfaces are peppered with dark starspots and bright faculae. TRAPPIST-1’s surface features have contaminated observations of other planets in the system, as described in previous research, and these observations of TRAPPIST-1e were not exempt from the star’s meddling. Luckily, researchers are conducting further JWST observations that should help disentangle the star’s impact; an ongoing program will capture closely spaced transits of TRAPPIST-1e and TRAPPIST-1b, which trace nearly the same track across the star’s disk. Since TRAPPIST-1b appears to be a bare rock, any features that are shared between its spectrum and TRAPPIST-1e’s are likely to come from the star. Identifying these features will allow for better characterization of TRAPPIST-1e’s spectrum and atmosphere.

Citation

Ana Glidden et al 2025 ApJL 990 L53. doi:10.3847/2041-8213/adf62e

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Astronomers often assume that sub-Neptune exoplanets have magma oceans hiding beneath their atmospheres. New research suggests that this might not always be the case.

Puzzling Type of Planet

In the 30 years since the discovery of the first exoplanet, astronomers have come to appreciate that many of the most common planets in our galaxy look nothing like the worlds in our solar system. One type of planet in particular appears to be ubiquitous despite not appearing in our own cosmic neighborhood: sub-Neptunes. As their name suggests these planets are slightly smaller than Neptune, but still much larger than Earth or what we’d expect from a planet composed mostly of rock.

What sub-Neptunes are made of and how they formed are still mysteries under active investigation by the research community. It is possible that these worlds are mostly rocky and sport puffy, light atmospheres over their surfaces; it’s also possible that these worlds are watery, and that most of their mass comes from heavy, steamy atmospheres. In most cases, though, it’s assumed that the high pressures and temperatures at the surfaces of these worlds foster a permanent, fiery magma ocean.

This key assumption that there’s no solid surface to stand on influences our models about how these planets cool and evolve over time. However, new research led by Bodie Breza (University of Maryland) suggests that this premise might not always be appropriate.

Solid Ground

To test the assumption that every sub-Neptune has a magma ocean, Breza and collaborators simulated hundreds of thousands of feasible exoplanet interiors and atmospheres. Each simulation slightly tweaked various characteristics, like the surface temperature or the planet’s total mass, then checked whether the temperature and pressure conditions at the planet’s surface would leave any rocks in solid or liquid form.

Somewhat surprisingly, the team found that about a third of the models they simulated had solid, not magma, surfaces. They found there were two distinct ways to solidify the magma and create a firm shell. First and most intuitively, if the surface temperature falls low enough, the magma will simply freeze. Second and more intriguingly, they found that a planet can also suppress a magma ocean if its atmosphere is heavy enough to drive up the surface pressure beyond the solid–liquid threshold.

This latter result is particularly insightful in light of recent JWST observations that suggest many sub-Neptunes have heavy atmospheres. These new models suggest that these worlds might have solid surfaces, and that models attempting to explain their compositions should be tweaked to account for this finding. In these early days where astronomers are still puzzling out the most basic properties of these strange worlds, research like this demonstrates the power of using advanced theoretical modeling to help interpret our cutting-edge observations.

Citation

“Not All Sub-Neptune Exoplanets Have Magma Oceans,” Bodie Breza et al 2025 ApJL 993 L46. doi:10.3847/2041-8213/ae0c07

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What would happen to a gaseous exoplanet if it was struck by a protoplanet? Recent research suggests that it would ring like a bell, and that just maybe, we’d be able to observe this ringing back on Earth.

Heavy Metal Mystery

Previous studies have hinted that giant planets have more heavy elements in their cores than we’d expect if they had formed from the exact same stew of gas and dust as their host stars. How exactly they end up with these enriched compositions is something of a mystery, though. Astronomers have proposed two potential theories: one somewhat dull, and one that involves dramatic collisions between the massive protoplanets.

In the first case, perhaps growing giant planets clear out the gas along their orbits, then steadily and quietly accrete the dust that spills over into the gaps. In the latter case, theorists have conjured a model in which growing gas giant planets repeatedly collide and merge with large and somewhat rocky protoplanets. Both of these mechanisms would produce the enhanced heavy element contents observed today, so how can we tell these two paths apart? Recent work by a team led by J.J. Zanazzi (University of California, Berkeley) proposes one such test.

Ringing Planets

Through mathematical derivations, the researchers demonstrate that if a gas giant were to collide with a protoplanet, the impact would cause the planet’s surface to physically oscillate inwards and outwards, and for its surface temperature to vary. In other words, the planet would “ring” like a bell struck with a hammer, and as it physically convulses in the aftermath of the merger it would grow brighter and fainter in a repeating, periodic pattern. In principle, if the ringing lasts for long enough and the oscillations in brightness were large enough, observers back on Earth could record the amplitude and period of the changes and back out some constraints on what had happened and when.

Excitingly, the researchers demonstrate that not only would the oscillations last for millions of years, they would also be bright enough for JWST to detect for one specific planet named Beta Pictoris b. Should this world have undergone a merger in the last 18 million years, just a few hours of observations with JWST’s Near-Infrared Camera would reveal 45-minute pulsations in which the planet’s brightness changes by about 1%. Since the planet is too far away from its host star for these oscillations to be caused by any gravitational interactions, detecting any periodic signal would be a slam-dunk for the major merger theory.

Beta Pictoris b is a young planet in a system that’s still forming, and it orbits its host star on an eccentric path that takes it through dense regions of the disk. Hopefully, future observations will test whether this treacherous path produced any massive collisions in the relatively recent past. Until then, though, we can all enjoy charming visions of massive planets colliding with one another and ringing through the night.

Citation

“Seismic Oscillations Excited by Giant Impacts in Directly Imaged Giant Planets,” J. J. Zanazzi et al 2025 ApJ 993 3. doi:10.3847/1538-4357/ae04ec

The post Planets Can Be Bells: The Aftermath of Major Mergers appeared first on AAS Nova.

Have you ever eaten a meal so quickly that you started to glow? Although this behavior likely isn’t relatable for most humans, astronomers are beginning to find more and more baby planets doing just that.

Planetary Glow Up

Planets are, famously, quite large. But astronomers know that they don’t start out that way, and that instead, stars and planetary systems start as wispy collections of dust and gas. This raw material eventually compresses itself into stars and planets and life capable of contemplating such things, but how exactly that happens is not perfectly understood.

Astronomers have the broad contours sketched out at least. Protoplanets destined to become gas giants like Jupiter and Saturn start by gobbling up all the material around them and eventually clear out gaps in the disks in which they are born. What little material flows into these gaps gets sucked onto the planet in a process called accretion, though exactly where this material lands and how gravity and magnetic fields interact is up for debate.

A number of different mechanisms predict that during this process, the protoplanet should emit light at a certain frequency associated with electrons jumping between energy levels in hydrogen atoms — what astronomers call Hα emission. In other words, they should glow at that specific wavelength only when they are accreting, though how strongly and consistently will depend on exactly what is happening around the planet.

These ideas existed only on paper until 2019, when a team first observed two glowing, growing planets around the star PDS 70. Recently, however, a powerful new instrument has begun collecting data, and astronomers just announced it has found another similar protoplanet: WISPIT-2b.

A New Discovery

A team of researchers led by Laird Close (University of Arizona) announced the discovery of this new world after analyzing images taken with the powerful new MagAO-X instrument on one of the 6.5-meter Magellan telescopes in Chile. The team outfitted the camera with a narrow filter that only admitted the Hα emission associated with accretion, then collected thousands of images over about two hours in April 2025. After stacking and post-processing their data, a faint dot jumped out beside the central star, right in the gap between two bright rings in the star’s disk.

This protoplanet, which the authors name WISPIT-2b in honor of their Wide Separation Planets in Time (WISPIT) survey, is likely about five times the mass of Jupiter and only 5 million years old, making it a baby on astronomical timescales. Based on how strongly it’s glowing, the team estimates that it’s accreting the equivalent of about 100 times the mass of Phobos, Mars’s largest moon, each year. This process won’t continue forever, as eventually the remains of the star’s disk will disperse and the planet will have to go hungry.

This remarkable find is only the third protoplanet unambiguously found to be embedded within a disk, and the first to be found in the gap between rings in a disk. With MagAO-X collecting data and the WISPIT survey underway, we’re likely in store for many other discoveries in the coming years. With enough observations and examples of these growing worlds, astronomers will fill in their models of how exactly giant planets as we know them are formed.

Citation

“Wide Separation Planets in Time (WISPIT): Discovery of a Gap Hα Protoplanet WISPIT 2b with MagAO-X,” Laird M. Close et al 2025 ApJL 990 L9. doi:10.3847/2041-8213/adf7a5

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Astrometric Methods for Detecting Exomoons Orbiting Imaged Exoplanets: Prospects for Detecting Moons Orbiting a Giant Planet in α Centauri A’s Habitable Zone
Authors: Kevin Wagner et al.
First Author’s Institution: University of Arizona
Status: Published in ApJL

Six of the eight planets in our solar system host at least one moon; the innermost planets Mercury and Venus are the exceptions. The origins of these moons are widely studied and hotly debated. Earth’s very own moon seems to have formed in the aftermath of a collision between the young Earth and another protoplanet. Mars seems to have captured two asteroids as its moons, Phobos and Deimos, a process thought to have produced many of the irregular satellites orbiting the gas giants as well. Using our solar system as a model, the presence of moons seems like a natural outcome of planet formation.

Why then don’t we observe exomoons, moons orbiting any of the ~6,000 known exoplanets? Well, the largest moon in our solar system, Ganymede, is 2.5% as massive as Earth and has 40% of the radius, making it marginally larger than Mercury but still less massive. You might have heard how difficult it is to find Earth-like exoplanets, and finding exomoons is even harder. A few exomoon candidates have been announced via microlensing and transits, but the authors of today’s article investigate whether a different technique, astrometry, could help find moons.

Astrometry involves precisely tracking the positions of objects like stars or planets on the sky. In a simple star–planet system, the star and planet trace out ellipses around their shared center of mass. With a moon present, there is an additional deviation, as the planet wobbles to and fro due to the gravitational tug of the moon. The authors of today’s article check whether moons can be detected by tracking such wobbles exhibited by directly imaged planets.

To start, the authors consider whether any known planets are promising targets for astrometric moon searches. There just so happens to be a giant planet candidate in Alpha Centauri, and if there were a massive moon orbiting this large planet around this nearby star, it would be as good as it gets. The authors simulate orbits of this system (a Saturn-like planet in a 1.8 au orbit around a Sun-like star at a distance of 4.2 light-years) with a 30-Earth-mass moon injected. They simulate observing such a system with a space-based 6.5-meter telescope (similar to the planned Habitable Worlds Observatory) with realistic noise over a 3-year observing campaign. The simulated and modeled orbits are shown in Figure 1. After the authors subtract the best-fit planet orbit, they are left with what is shown in Figure 2, where a clear periodic perturbation from the moon as it orbits is visible.

The authors then repeat this procedure with more realistically sized moons and a more optimistic observing campaign (5-year baseline, 1-hour observing cadence, precision of 0.1 milliarcsecond) looking at the Alpha Centauri giant planet candidate. They use the difference in the chi-squared (χ²) test statistic to determine whether the presence of a moon is statistically preferred. Figure 3 shows the moon-induced deviations for two different moon masses and the resulting χ² difference. Using their χ² difference threshold of ~5, the lowest-mass detectable moon is ~0.2 Earth mass. This is much more massive than the Moon, which is around 1% of Earth’s mass. The authors additionally vary the moon’s orbital period and find that periods of 4–30 days are detectable. The authors continue to consider more specific observing scenarios: a 39-meter ground-based telescope (similar to the planned European Extremely Large Telescope) and a 3-meter space telescope built specifically to find moons. They find that the ground-based telescope observing once per day could detect an Earth-mass moon around a Saturn-like planet over a 5-year observing campaign. The dedicated space telescope observing once per hour could make the same detection observing over 5 years. While detecting moons astrometrically is neither easy nor fast, it may be feasible to start finding moons around planets orbiting nearby stars in the coming decades.

All of this is great news for fans of the hit movie (and still the highest-grossing movie of all time) Avatar, which features a habitable exomoon in the Alpha Centauri system. Searching for moons will help us understand their properties and formation, probe whether our solar system is unique, and even look for life on rocky moons orbiting gas giants in the habitable zones of their stars.

Original astrobite edited by Ryan White.

About the author, Kylee Carden:

I am a PhD student at Johns Hopkins University, where I am an observer of planets outside the solar system. I’m interested in dynamics, disks, demographics, the Roman Space Telescope. I am a huge fan of my cat Piccadilly, cycling, and visiting underappreciated tourist sites.

The post Finding Avatar’s Pandora: Exomoons with Astrometry appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The Gap–Giant Association: Are Planets Hiding in the Gaps?
Authors: Caleb Lammers and Joshua Winn
Authors’ Institutions: Princeton University
Status: Published in ApJ

The Kepler space telescope played an almost decade-long game of hide-and-seek. After nine and a half years of operation, Kepler detected more than 2,700 planets outside of our solar system primarily by using the transit method, which is particularly efficient at detecting planets that orbit close to their host stars. Astronomers have also been detecting planets with the radial velocity technique, which is better at finding larger planets at longer orbital periods. By looking for planets with both the transit and radial velocity techniques, astronomers can look for both close-in and far-out planets to paint a more complete picture of other solar systems in our galaxy.

Using the Kepler Giant Planet Survey, the authors of today’s article found that among the 26 systems with three or more transiting planets, four were found to also have an outer giant planet. They quickly noticed that instead of an evenly spaced out inner system of planets, every single one of these four systems with the outer giant planets revealed a notable gap between two of their inner planets. They dubbed this phenomenon the “gap–giant association” — in other words, when an outer giant planet exists in a planetary system, there is evidence of a large gap between two of the inner planets, as shown in Figure 1. This pattern has been observed before, but there has been little theoretical work to explain the effects of outer giants on orbital spacings. In today’s article, the authors ask the question: are there planets inside the gap hiding from us? To address this, they conduct simulations to see if (a) these systems can host a hiding planet in their gaps without becoming dynamically unstable and (b) if such a planet can remain hidden when looked for with the transit method.

Close Your Eyes and Count to N

The authors of today’s article model these four systems (Kepler-48, Kepler-65, Kepler-90, and Kepler-139) with a planet added to their gaps and use an N-body simulation (i.e., fancy physics calculations that track how planets gravitationally interact) to evolve the systems over time and evaluate their long-term stability. They find that each of these injected planets has a high survival rate, which means that each of these four systems could stably host an additional ~2–20 Earth-mass planet in its gap for billions of years without falling apart. The authors then calculated whether the outer giants could “hide” these theoretical gap planets by tilting the planets’ orbits enough so that they would not be detectable with the transit method. In order to do this, the outer giant would have to exert a large enough gravitational force on the gap planet to cause it to precess at a rate independent of its neighbors, allowing its orbital inclination to grow. However, they found that the outer giant planets are either too far away or not massive enough to do the job.

Only one system, Kepler-90, has an outer giant that could potentially tilt the gap planet’s orbit enough for it to fly under the radar if the giant were also on a modestly inclined orbit. However, previous detections of Kepler-90’s outer giant suggest that its orbit is well-aligned with those of the inner system, making this hypothesis implausible. They therefore concluded that it is unlikely that planets between ~2 and 20 Earth masses are hiding within these gaps.

Seeking Out Another Option

Before completely abandoning this hypothesis, the authors propose that maybe the gaps do contain planets, but they’re just too small for Kepler to detect. They calculate the detection efficiencies as a function of planet radius and orbital period for each of the four systems and find that planets smaller than about ~0.5–1 Earth radius could have gone unnoticed (as shown in Figure 2). While this would make these systems slightly unusual (most multiplanetary systems have relatively uniform planet sizes), it’s not completely impossible. However, they don’t rule out the possibility that these gaps are truly empty, and that the presence of an outer giant could prevent planets from forming in certain regions or disrupt their orbits after formation. While it is hard to draw any firm conclusions with a sample size of four systems, this study highlights how much we still don’t understand about planetary system architecture, and therefore planetary formation and evolution.

Though the Kepler mission has come to an end, ongoing radial velocity surveys will continue to expand the sample of systems like these four so astronomers can get a clearer picture of what’s behind this gap–giant association.

Original astrobite edited by Annelia Anderson.

About the author, Tori Bonidie:

I am a 5th-year PhD candidate studying exoplanet atmospheres at the University of Pittsburgh. Prior to this, I earned my BA in astrophysics at Franklin and Marshall College where I worked on pulsar detection as a member of NANOGrav. In my free time you can find me cooking, napping with my cat, or reading STEMinist romcoms!

The post Planetary Hide and Seek appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Clouds Can Enhance Direct-Imaging Detection of O₂ and O₃ on Terrestrial Exoplanets
Authors: Huanzhou Yang, Michelle Hu, and Dorian S. Abbot
First Author’s Institution: University of Chicago
Status: Published in ApJ

In the hunt for life beyond Earth, studying exoplanet atmospheres is one of our most powerful tools. The atmosphere of an exoplanet acts as a window into its environment and allows astronomers to take a guess at what processes are shaping the planet’s climate, chemistry, and thus, its potential for habitability. The gases present in the planet’s atmosphere impart a unique spectral fingerprint on the light that passes through the atmosphere and allows us to identify what gases might be present and look for possible signs of life.

JWST is already hard at work looking at distant worlds and gathering spectroscopic data for us to analyse. It has already observed several exoplanets and recorded the light that passed through their atmospheres. This has not only sparked a debate over what could be interpreted as the first possible signs of biological activity, but has also given us a glimpse of worlds that are remarkably different from our own.

However, JWST is mostly limited to observing the atmospheres of transiting exoplanets. That means planets that orbit close to their host star and are more or less directly edge-on, as viewed from us, so that they transit across the face of the star. The only planets that the telescope is able to observe directly are big, young, and hot planets farther from their host star, at distances more resembling those of the outer planets in our solar system, like Saturn or Uranus. If only we had a telescope powerful enough to image a potentially habitable planet directly and analyse the light reflected from it.

The Habitable Worlds Observatory

This is where the Habitable Worlds Observatory (HWO) will come in. Now, I know what you are thinking. Why must astronomers always look towards greener pastures bigger telescopes when we already have perfectly functional space telescopes in orbit or practically on the launch pad? Well, it is true that the next flagship space telescope from NASA, the Nancy Grace Roman Space Telescope, is designed to directly image exoplanets and analyse their atmospheres. But space telescopes can take decades to plan and are often built on lessons learned from previous missions. Roman, with its 2.4-meter primary mirror and coronagraph, will be able to observe planets similar in size and orbital distance to Jupiter and will get us some of the way, for sure, but not all the way. At three times the mirror size, HWO, NASA’s proposed successor to Roman that is planned for the 2040s, will carry the torch even further and be able to directly image Earth-like planets in the habitable zone, where liquid water can exist on the planet’s surface.

But It Might Be Cloudy Tomorrow

This brings us to today’s article. If the HWO is going to potentially observe Earth analogues, we might expect it to run into the same issue that plagues everyone living in the UK for most of the year — clouds. Clouds in the atmosphere of an exoplanet can sometimes cause trouble when trying to analyse the light. Cloud particles scatter different wavelengths of light differently, and cloud variability creates dynamic changes in the observed brightness that can make it hard to know what exactly you are looking at. Clouds can also mean varying levels of opacity to look through depending on cloud composition, and they can hide underlying atmospheric properties such as water content beneath a thick cloud layer. For transmission spectroscopy, even a thin layer of clouds can disrupt the measurements as the light has to travel a long distance through the atmosphere. However, for direct imaging, the effect of clouds is perhaps more nuanced. While a thick cloud deck will block the signal from whatever gas lies beneath it, it will also increase the overall albedo of the planet and make it easier to detect the gas above. This means that cloud height and type are both critical variables in understanding atmospheric properties of exoplanets, which is what the authors of today’s article set out to investigate.

To understand how clouds affect the ability to detect signs of life on distant Earth-like planets, the authors used computer simulations. They focused on two gases, molecular oxygen (O₂) and ozone (O₃). Both gases are often regarded as biosignatures, although their astrobiological significance has been debated. The authors first used a tool that simulates how a telescope like the HWO might observe an Earth-like planet around a star 15 parsecs away. This tool predicts how light bounces off a planet’s surface and atmosphere, and whether the two gases would show up clearly in the reflected light. Next, they created realistic cloud conditions using a cloud microphysics model. This model calculates how clouds might form and behave depending on factors like surface pressure or how much sunlight the planet gets. With this they were able to change things like cloud height and particle size. They then combined the two tools by adding the simulated clouds into the observations model and building a mathematical model to help explain what they saw in the simulations. The sketch for their model can be seen in Figure 1.

A Cloudy Sky Can Actually Be a Good Thing

The researchers discovered that low clouds can actually make gases like oxygen and ozone easier to detect, because these clouds reflect more light without blocking the gases above them. On the other hand, high clouds can make it harder since they can hide the gases from view. They tested different cloud types using real data from Earth as seen in Figure 2. They looked at five common cloud types, like stratus (flat and low), cirrus (high and wispy), and deep convective clouds (tall, thunderstorm-like), and compared them to their model clouds (labelled as CARMA in the figure).

They found that most clouds improved detection, especially if the cloud droplets were small (as they reflect more light). Stratus clouds and deep convective clouds gave the strongest boost to detection, because they have a lot of water and are either low (stratus) or extend through many layers (deep convective). Ozone saw the biggest bump in detectability as it is concentrated higher in the atmosphere, which means that it is in the region above most clouds where the increased reflection from the cloud layer below makes it easier to spot. This means that unlike the case for transit spectroscopy where clouds interfere with the detection of gases, for direct observations of the reflected light, clouds may actually be a good thing. This insight into the role of clouds in exoplanet atmospheres not only refines our current understanding but also helps guide the design of future telescopes, like the HWO, and our search for life on these remote worlds.

Original astrobite edited by Maria Vincent.

About the author, Kasper Zoellner:

I have a Master of Science in astronomy and I am currently working towards a PhD in physics and educational science. My greatest passion is the search for exoplanets and how stellar variability may influence the possibility of life. I am also interested in science outreach, education, and discussing what sci-fi novel to read next!

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JWST observations of a nearby star’s debris disk recently revealed what may be one of the lowest-mass planets ever imaged.

How to Find a Small Planet

Though it remains a formidable technical challenge, astronomers have gotten fairly good at taking images of planets around other stars by carefully blocking the light of the host and searching for the small points of light that remain. However, though this technique is well-suited for discovering large, bright, high-mass planets, their lower-mass cousins below the size of Jupiter remain challenging to detect. To get pictures of these smaller worlds, astronomers must resort to detective work and search for signs of their presence through indirect means.

One promising approach is to look not for the planet itself, but rather its effect on the dusty disk of material around the star. These structures, called debris disks, are constantly replenished by planetesimals colliding and grinding one another to dust. If a planet happens to orbit within this disk, it will “stir” the dust into distinctive patterns including rings and spiral arms. If astronomers observe that a star has a debris disk with gaps or spirals, they can analyze those substructures and deduce where a planet might be hiding.

The Star of this Show: TWA 7

TWA 7 is a tiny M-dwarf star just over 100 light-years from Earth. Data from the Spitzer Space Telescope revealed that TWA 7 was unusually bright when observed at infrared wavelengths, which hinted that there might be a warm, dusty disk surrounding the star. Follow-up observations with the Hubble Space Telescope and several major ground-based facilities confirmed that this star successfully met all the conditions listed above: TWA 7 is surrounded by a face-on debris disk with rings and a faint spiral arm. Using all of this information, astronomers predicted that a Saturn-mass planet might lie in a low-density pocket of the disk just beside the star.

This prediction led to a search with JWST last summer. Initial observations taken at mid-infrared wavelengths revealed a bright dot sitting near the predicted location of the planet. However, with just these observations, it was hard to confidently say that this source wasn’t just a distant background galaxy that happened to appear there by chance. To help settle the matter, JWST took another look in two different near-infrared wavelength bands a few weeks later.

Revisiting TWA 7

A team led by Katie Crotts (Space Telescope Science Institute) recently published these later observations. These new data show a dot in the exact same place as before, and with a color that’s much more planet-like than galaxy-like.

While this adds plenty of evidence to the planetary interpretation, the team cautions that one more set of follow-up observations is needed to be confident that this is, in fact, a planet. Assuming future observations back up these first hints, however, this would be the lowest-mass planet ever imaged, and a happy conclusion to a detective story that started with dust.

Citation

“Follow-Up Exploration of the TWA 7 Planet–Disk System with JWST NIRCam,” Katie Crotts et al 2025 ApJL 987 L41. doi:10.3847/2041-8213/ade798

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By pushing JWST to its limits, astronomers may have just spotted a planet around the nearest Sun-like star, Alpha Centauri A. Though another look at the star is needed next year to confirm the finding, if the detection holds up, this discovery easily earns several superlatives: the planet would be the nearest, oldest, coldest, and lowest-mass world ever directly imaged beyond our solar system.

Hi, Neighbor!

The scale of our Milky Way galaxy is hard to comprehend with our Earth-bound minds that are more attuned to measuring distances in miles than in light-years. However, even though our suburban stellar neighborhood is tens of thousands of light-years from the galactic downtown, it is not empty: there are a handful of nearby systems that offer unique opportunities to study stars and their potential planet children “up close.”

The nearest star system to the Sun at just over 4 light-years away is called Alpha Centauri. It’s a star “system” since what appears to the naked eye to be one star is actually three objects orbiting each other: Alpha Centauri A and Alpha Centauri B are two Sun-like stars that circle each other every 80 years or so, while Alpha Centauri C, better known as Proxima Centauri, circles the inner pair on a much wider orbit.

Though Proxima Centauri is the most famous of the trio, since it’s technically the closest star to the Sun, its larger siblings are arguably better targets for searching for planets. Since these stars are more massive, their habitable zones are large enough that astronomers can block out the star itself and search the surrounding area for planets using a tool called a coronagraph.

Challenging Observations

Back in 2019, a team of astronomers using a coronagraph on the Very Large Telescope uncovered tantalizing evidence of a giant planet orbiting Alpha Centauri A. However, confirming or rejecting this initial peek using telescopes on Earth’s surface was challenging. When JWST finally launched in 2021, following up on this hint was a top priority. Astronomers first attempted to point JWST toward the Alpha Centauri system in 2023, but unfortunately, the observations from that attempt were unusable.

Though one might think aiming a telescope at a nearby star is easier than taking a look at something more distant, this is unfortunately not the case. For one thing, the stars of the Alpha Centauri system are bright enough to overwhelm JWST’s sensitive detectors without careful calibration. For another, keeping the telescope locked on target and the star behind the coronagraph requires continuous tweaks to account for the Sun’s motion relative to Alpha Centauri, JWST’s motion relative to the Sun, and Alpha Centauri A’s motion relative to Alpha Centauri B. The team regrouped, tested a new observing strategy in mid-2024, then took three long observations in August 2024, February 2025, and April 2025.

A Planet Candidate

This time, the observations went off nearly without a hitch. After careful data processing, the team led by Charles Beichman and Aniket Sanghi of the California Institute of Technology found a bright blob positioned right beside the star in their August data. Interestingly, the blob disappeared in the next two observations. Working on the hunch that this blob was the same object as the planet candidate seen by the Very Large Telescope, the team realized that most allowed orbits would place the planet too close to the star to be visible in those later observations. In other words, the planet might be playing hide-and-seek, peeking out from behind the star in one month only to vanish in the next.

The authors estimated that the source is a 1–1.1 Jupiter radius planet with a mass of 90–150 Earth masses (0.28–0.47 Jupiter mass) on a 2–3-year orbit. The team stressed that with just one detection, this should still be regarded as a planet candidate, not a confirmed discovery. If the planet is eventually verified, however, it stands out among its peers as the first mature, cold planet ever imaged within its star’s habitable zone. Future detectors may be able to collect spectra of the planet itself, unlocking new insights into giant planet evolution and composition in multiple-star systems with nested orbits, like the Alpha Centauri system.

Now that JWST has a proven strategy for observing this challenging system, it should be possible to take follow-up images. If the planet is real and traveling on its expected orbit, it should reappear beside Alpha Centauri A in August 2026. Hopefully, JWST will be looking when it does, and we can finally confirm that we have a planetary neighbor next door.

Citation

“Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits,” Charles Beichman et al 2025 ApJL 989 L22. doi:10.3847/2041-8213/adf53f

“Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis,” Aniket Sanghi et al 2025 ApJL 989 L23. doi:10.3847/2041-8213/adf53e

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Unveiling the Interior Structure and Thermal Evolution of Super-Earth GJ 486b
Authors: Chandan K. Sahu et al.
First Author’s Institution: National Institute of Science Education and Research, India
Status: Published in ApJ

Planets between the sizes of Neptune and Earth, known as super-Earths, are the most frequently found planets in the galaxy. With no analog in our solar system, these worlds can offer a unique look at planet formation and evolution, and potentially life in the universe. To truly understand a planet’s environment and assess its potential for habitability, we must look at every part of it. This includes not just the atmosphere, but also the interior. Rocky planets, such as the inner solar system planets, typically don’t have enough gravitational pull to retain their primary atmospheres. Thus, only their secondary atmospheres remain. These secondary atmospheres are directly linked to the interior of the planet and are usually formed by volcanic outgassing, material from impacts on the planet’s surface, and other interior processes. By observing a rocky planet’s atmosphere and determining its composition, we can learn something about the interior of the planet as well.

The subject of today’s article, GJ 486b, is a warm super-Earth orbiting an M-dwarf star every 1.5 days. The transmission spectrum of the planet was recently observed by JWST, and when the data were analyzed, a potential water-rich atmosphere was discovered! Today’s authors take these recent discoveries of GJ 486b’s atmosphere and use them to model the interior of the planet.

One Model to Rule Them All

The interiors of rocky planets are not very well known. This is because the best way to understand what’s inside a rocky planet is through seismology. In order to do this, one must put a seismograph on a planet’s surface and measure how seismic waves move through the material inside the planet. Only three bodies have had seismographs landed on them: Earth, the Moon, and Mars. Rocky exoplanet interiors are even harder to understand when the only properties we know are the planet’s mass, radius, and certain aspects of its atmosphere. To understand exoplanet interiors, we have to use modeling to infer properties of the inside of the planet.

The authors of today’s article use the 1-D modeling package SERPINT (“structure and evolution model for rocky planet interiors”) to model GJ 486b’s interior based upon JWST observations of its atmosphere and assumptions made about rocky planets. Their model is broken down into four different parts, as illustrated in Figure 1.

In the structure module, the authors model the layers in the planet. They assume an Earth-like interior structure with an iron core, an inner mantle, and an outer mantle. The crust is not modeled as it’s considered a very complex structure and outside the scope of the article. The thermal module takes into account how the host star’s light changes over time and the radioactive decay of elements in the planet’s interior. The volatile module models the water and oxygen in the planet and how they are exchanged between the interior, surface, and atmosphere. Finally, the escape module looks at how the atmospheric escape of elements such as hydrogen and oxygen affect the atmosphere (and therefore the interior) over time.

Taking all of these factors into account is important when creating a comprehensive picture of a planet. Each module models different processes that influence the planet’s interior, surface, and atmosphere, making sure that we’re taking all of these things into account when trying to understand the planet. It truly is one model to rule them all.

Outgassing and Photolysis and Escape, Oh My!

The authors start the model for the planet and star together and allow them both to evolve for 10 billion years. The planet starts with a mantle temperature of 5000K, which ensures the surface is molten, creating a magma ocean. This is typically how we think all rocky planets, including Earth, started their formation. Figure 2 illustrates how the mantle solidifies over time, influencing the overall structure of GJ 486b. Both layers of the mantle start to cool after the start of the simulation, and the lower mantle cools and solidifies first, followed by the upper mantle. This is due to the different composition in each layer and thus, a different temperature at which they will solidify. Cooling is delayed for a while due to internal heating from radioactive decay of the elements. This can be seen in Figure 2b with the shallow slope of the orange line. The orange line represents the mantle’s equilibrium temperature, and the yellow shaded region is the time in which the mantle has not yet solidified. As the mantle cools, it turns into a thick mush and then eventually into solid rock (as shown in Figure 2d). This indicates the mantle has solidified, and we move from the yellow shaded region on the graphs into the orange shaded region.

The authors start the simulation with 10 Earth oceans of water on the planet. This water is initially inside the magma ocean, but as the mantle cools and solidifies, some of the water becomes solid while the rest of it is transferred to the atmosphere in the form of water vapor. Water vapor outgassing from the interior of the planet stops when the mantle becomes solid. At this same time, the luminosity of the host star shrinks (as shown in Figure 2a), causing the atmospheric escape of hydrogen and oxygen to stop and for atmospheric water vapor to stop being broken down by radiation from the host star (known as photolysis). This results in a buildup of oxygen and water over time. This final atmospheric composition matches the transmission spectroscopy data from JWST. This exchange between outgassing, the breaking down of atmospheric water vapor and hydrogen/oxygen escape impacts the planet’s sources of water (shown in Figure 3) and influences the atmosphere we see on GJ 486b today. Today’s article summarizes the possible interior structure of the super-Earth GJ 486b. While the modeling is able to reproduce the atmospheric data obtained with JWST, there are many limitations to the model. First, it assumes a simplified version of Earth’s interior structure, when in reality, Earth’s structure has a much more complex composition and these minerals are distributed non-uniformly across Earth’s layers. This can result in different temperatures and pressures for each layer, something that was not modeled in this article. It’s challenging to determine the composition of rocky exoplanets, and because super-Earths are much larger than Earth, the pressures inside of the planet will be more extreme, leading to unknown effects on the materials inside. Furthermore, GJ 486b is expected to be tidally locked, presenting a whole new set of assumptions and challenges to modeling its interior. And lastly, even though there is evidence to suggest that GJ 486b could have a water-rich atmosphere, the JWST transmission spectrum could also be attributed to starspots on the host star, making the assumption of a water-rich atmosphere wrong. While this is a good first step, more data and new ways to understand the interiors of exoplanets will be needed to truly understand what is going on inside GJ 486b.

Original astrobite edited by Tori Bonidie.

About the author, Kaz Gary:

I am a third-year PhD student at The Ohio State University with a focus in exoplanetary science. My current work focuses on modeling exoplanet observations for two upcoming space-based telescope missions: the Twinkle satellite and Habitable Worlds Observatory. Outside of research, I help develop exoplanet-focused shows for the Arne Sletteback Planetarium at OSU. In my free time, I enjoy playing tabletop RPGs, painting, watching terrible reality TV, and hanging out with my pet hedgehog.

The post What’s Going On Inside GJ 486b? appeared first on AAS Nova.

There’s been a lot of astronomy in the news lately! Many recent news stories have featured research published in the AAS journals, so today we’re taking a look at four research articles that have recently gotten attention from the media.

New Horizons Navigates by the Stars

Starting closest to home, the first article describes a technological demonstration that took place on the edge of our solar system. In the nearly 20 years since its launch, the New Horizons spacecraft has ventured from Cape Canaveral to its current berth in the Kuiper Belt, roughly 61 au (5.7 billion miles or 9.1 billion kilometers) from Earth. In that time, New Horizons became the first spacecraft to venture close to Pluto and its moons as well as a second Kuiper Belt object called Arrokoth.

New Horizons has also traveled a large enough distance for nearby stars to shift their positions relative to the background of more distant stars, enabling a measurement of the spacecraft’s position in space. Tod Lauer (NSF National Optical Infrared Astronomy Research Laboratory) and collaborators demonstrated this ability using New Horizons Long Range Reconnaissance Imager (LORRI) observations from April 2020, when the spacecraft was 47 au from the Sun. The stars used for the parallax measurements were Proxima Centauri and Wolf 359, two of the nearest stars to Earth. The team measured the stars’ positions relative to the positions of background stars and compared the results to observations made from Earth.

From the apparent shift in position of the two stars, the team determined the location of the spacecraft in space as well as the error in their measurement. They were able to ascertain the position of the spacecraft to within 0.44 au of its true position.

Though this measurement is far less accurate than localization with the Deep Space Network, it’s still an important step toward understanding the future prospects for autonomous spacecraft navigation via the stars. Looking ahead to future interstellar navigation systems, the team showed that measurements of a few nearby stars (Proxima Centauri and Barnard’s Star are the best bets for journeys within tens of thousands of astronomical units of the Sun) are more useful than measurements of a larger number of more distant stars. Basing measurements on a larger number of images to cut down on random scatter in the position of the star would also improve the results, as would simply using newer instruments. Ultimately, other types of navigation systems, such as those based on measurements of pulsars, are more likely to reach the precision necessary for autonomous spacecraft navigation. However, this method remains interesting, given that the straightforward nature of the imaging and analysis is already well within the capabilities of modern spacecraft systems.

First Detection of Semiheavy Water Ice Around a Low-Mass Protostar

Next up is a discovery from 457 light-years away in the Taurus molecular cloud. With a mass of 0.3–0.5 solar mass, a disk spanning 75–125 au, and a surrounding envelope of 0.9 solar mass, the isolated low-mass protostar L1527 is likely to grow into a star of similar mass to the Sun. That makes it an excellent target for investigating how planetary systems like our own acquire critical molecules like water.

Katerina Slavicinska (Leiden Observatory) and coauthors used JWST to search L1527 for semiheavy water (HDO) — a water molecule in which one of the hydrogen atoms is replaced with a deuterium atom. HDO has been detected in many locations throughout our solar system, including in Earth’s oceans, and water in our solar system tends to contain a high abundance of HDO molecules. A high deuterium abundance can be linked to formation in a cold environment, suggesting that our solar system’s water may have formed in the icy clouds out of which the Sun and the planets were born.

Thanks to JWST’s high resolution and sensitivity, Slavicinska’s team was able to detect HDO ice in L1527, where previous, lower-resolution observations had only hinted at the presence of the molecule. They also measured emission from H₂O ice, yielding a ratio of the abundances of the two types of water. The ice HDO/H₂O ratio of L1527 is consistent with the gas HDO/H₂O ratios of other isolated low-mass protostars and 4–7 times higher than the gas HDO/H₂O ratios of clustered low-mass protostars. This difference may be due to differences in the star-forming environments of clustered protostars, or it may signal that the water in these protostars underwent gas-phase processing at some point. If environmental factors are the cause, that would suggest that L1527 should have a higher HDO/H₂O ratio than objects in our solar system, since the Sun likely formed in a cluster environment.

This study demonstrates JWST’s ability to investigate the chemistry of young stars and probe the chemical evolution of protostars and planetary systems. Slavicinska and coauthors identified two important next steps to advance our understanding of the chemistry of star- and planet-forming environments: 1) measuring gas-phase and ice-phase HDO/H₂O ratios in the same object to understand how gas-phase chemistry alters water around protostars and 2) measuring the HDO/H₂O ratios of larger samples of isolated and clustered protostars in order to understand the impact of environmental factors.

A Massive Planet Approaches Its Doom

TOI-2109b is an ultra-hot Jupiter exoplanet that orbits its host star every 16 hours, giving it the shortest period of any known hot Jupiter. Orbiting its host star so closely, TOI-2109b is susceptible to powerful tidal forces that can lead to an exchange of angular momentum between the planet and its home star, potentially causing the planet to spiral inward and be engulfed by its star.

Jaime Alvarado-Montes (Macquarie University) and collaborators investigated how and when TOI-2109b’s doom might come about. Critical to the discussion is the uncertain age of TOI-2109, which likely lies in the range of 1.09–2.65 billion years. If the star’s age is on the lower end of the range, TOI-2109b’s orbit would decay slowly (~4 milliseconds per year); if the star’s age is on the higher end of the range, the planet’s orbit would decay quickly (~1,100 milliseconds per year). The decay rate depends on the star’s age because planets lose their kinetic energy due to friction inside their host stars, and the efficiency of this process depends upon the interior structure of the star, which changes with age.

Alvarado-Montes and coauthors used data from the Transiting Exoplanet Survey Satellite (TESS), the CHaracterising ExOPlanet Satellite (CHEOPS), and multiple ground-based telescopes to constrain the rate of change of TOI-2109b’s orbital period. Taking into account changes in transit timing due to an outer planet candidate in the system, deviations from spherical symmetry, and other factors, the authors find a likely orbital decay rate of just 2.6 milliseconds per year. This is consistent with the rate predicted for a “young” host star, and it’s expected to shift TOI-2109b’s mid-transit time by a few seconds over a three-year period. This change is potentially detectable with high-cadence observations, helping to understand not just the fate of TOI-2109b, but of ultra-short-period planets as a whole.

Discovery of a Mysterious Long-Period Transient

Finally, Fengqiu Adam Dong (National Radio Astronomy Observatory; Green Bank Observatory) and coauthors recently described their discovery of an unusual long-period transient radio signal. Long-period radio transients exhibit signals that repeat with periods ranging from 10 seconds to multiple hours. While the exact origin of these signals remains unknown, researchers suspect that magnetic white dwarfs and neutron stars are the cause, with the two sources perhaps representing different classes under the long-period radio transient umbrella.

The signal was detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, which was searching for bursts of radio emission from pulsars within our galaxy. The newly discovered radio signal, which comes from a source named CHIME J1634+44, has a primary period of 841 seconds and a secondary period of 4,206 seconds, making it decidedly un-pulsar-like. Dong’s team performed follow-up observations of CHIME J1634+44 with the Very Large Array, the Neil Gehrels Swift Observatory, and the Green Bank Telescope. The Very Large Array and the Green Bank Telescope each detected two bursts from the source, bringing the total number of bursts reported in this study to 89.

CHIME J1634+44 is unusual in a number of ways. Its emission is almost entirely circularly polarized, meaning that the plane in which the electric and magnetic waves of the radio signal oscillates rotates in a circle as the signal travels through space. The time between pulses is also decreasing, slowly but steadily. If the pulsation period coincides with an object’s spin period, this means that the object is spinning faster as time goes on; this could occur if the source of the bursts is accreting material from a companion. If instead the pulsation period is linked to the orbital period of an object in a binary system, emission of gravitational waves could be causing the orbit to shrink.

What kind of object could produce this signal? Dong and coauthors considered binary systems containing either a white dwarf or a neutron star. Neither scenario perfectly fits the available evidence, but the team concluded that a binary system containing a neutron star is the likeliest source of the long-period, highly polarized, steadily accelerating pulses of CHIME J1634+44. The strongest evidence in favor of this scenario is that neutron stars are known to exhibit strongly polarized pulses of similar luminosity to those from CHIME J1634+44. Dong’s team expects that CHIME J1634+44 will remain an important test of theories of long-period radio transients — and as new information emerges about its identity, CHIME J1634+44 might just find its way into the news again!

Citation

“A Demonstration of Interstellar Navigation Using New Horizons,” Tod R. Lauer et al 2025 AJ 170 22. doi:10.3847/1538-3881/addabe

“HDO Ice Detected Toward an Isolated Low-Mass Protostar with JWST,” Katerina Slavicinska et al 2025 ApJL 986 L19. doi:10.3847/2041-8213/addb45

“Orbital Decay of the Ultra-Hot Jupiter TOI-2109b: Tidal Constraints and Transit-Timing Analysis,” Jaime A. Alvarado-Montes et al 2025 ApJ 988 66. doi:10.3847/1538-4357/ade057

“CHIME/Fast Radio Burst Discovery of an Unusual Circularly Polarized Long-Period Radio Transient with an Accelerating Spin Period,” Fengqiu Adam Dong et al 2025 ApJL 988 L29. doi:10.3847/2041-8213/adeaab

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