Cristobal Bordiu et al 2026 ApJL 1005 L34

Researchers have detected SO and SO₂ for the first time in an early-type evolved star; these results suggest that B[e]supergiants could be useful for studying sulfur chemistry under extreme radiation conditions.

The post Discovery of Sulfur Oxides in the Ejecta of a B[e] Supergiant appeared first on AAS Nova.

Light and dark regions speckle the Sun and other stars, complicating the interpretation of exoplanet transmission spectra. New modeling suggests that faculae — bright areas on the visible surface of the Sun — appear dark on cooler stars, adding a new wrinkle to this challenge.

Dark Spot, Bright Spot

It’s an adage as old as exoplanet science itself: know thy star, know thy planet. This recommendation is key when using transmission spectroscopy to tease out the components of an exoplanet’s atmosphere; the backdrop to this process is a rotating star dotted with ever-changing active regions, and the better the star’s behavior is understood, the more reliable the extracted spectrum becomes.

The Sun is freckled with dark spots — sunspots — as well as bright regions called faculae. Sunspots form where the Sun’s magnetic field bubbles up, creating pockets of cooler, less luminous plasma. Solar faculae form in regions of concentrated magnetic field, creating bright spots that line the dark crevasses between convective cells.

Other stars also have starspots and faculae, but thus far, astronomers have no direct observations of faculae on any star except the Sun. Out of necessity, researchers interpreting exoplanet spectra assume that faculae on other stars are similar to those on the Sun — but are they actually?

Would a Facula on Any Other Star Look as Bright?

To explore what faculae might look like on stars other than the Sun, Alexander Shapiro (University of Graz; Max Planck Institute for Solar System Research) and collaborators turned to three-dimensional radiative magnetohydrodynamics simulations and radiative transfer modeling. Their aim was to simulate the appearance and spectra of faculae on stars of spectral type G2, K2, M0, and M4 — from Sun-like to substantially smaller and cooler than the Sun.

The modeled faculae on the Sun-like G2 star were bright, as expected. On the K2 and M0 star, these features were fainter, with the faculae on the M0 star being roughly as bright as the surrounding stellar surface. On the M4 star, the faculae were darker than surrounding areas, upending the assumption that faculae on all stars are brighter than the stellar surface.

Exoplanetary Effects

The transition from bright faculae on Sun-like stars to dark faculae on M4-class stars directly affects interpretations of exoplanet transmission spectra. The existence of dark faculae increases the derived exoplanet radius, whereas bright faculae on Sun-like stars decrease the derived radius. The contamination due to the faculae is wavelength dependent, with the largest contamination occurring at shorter wavelengths. This contamination, if not fully accounted for, can mimic spectral features from an exoplanet’s atmosphere.

What determines whether faculae appear brighter or darker than their surroundings? Using a qualitative framework, Shapiro and coauthors found that the appearance of faculae can be traced to a few competing factors: the strong magnetic fields within faculae prevent the incursion of hotter material (making the spots appear darker), while the magnetic field lowers the opacity of the gas in that region, allowing us to peer deeper and glimpse hotter material (making the spots appear brighter). On cooler stars, effects related to higher surface gas pressure tilt the balance in favor of darker faculae.

Citation

“The Curious Case of Dark Faculae on M Dwarf Stars,” A. I. Shapiro et al 2026 ApJ 1008 24. doi:10.3847/1538-4357/ae7105

The post When Bright Spots Go Dark appeared first on AAS Nova.

Jamie Dietrich et al 2026 AJ 172 35

Some systems in the Habitable Worlds Observatory (HWO) Exoplanet Exploration Program (ExEP) Mission Star List have more than a 50% chance of hosting a temperate terrestrial exoplanet.

The post Predictive Rankings of the Probability of Hosting a Temperate Terrestrial World for the HWO ExEP Mission Star List 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: Thermal Electrons in the Radio Afterglow of Relativistic Tidal Disruption Event ZTF22aaajecp/AT 2022cmc
Authors: Lauren Rhodes et al.
First Author’s Institution: McGill University
Status: Published in ApJ

Tidal disruption events (TDEs, see Figure 1), which occur when a star gets a little too close to a supermassive black hole (SMBH) and gets ripped apart, are a hot topic across the electromagnetic spectrum. During a TDE, the star can no longer hold itself together under the gravitational pull of the SMBH. Some bits of the star end up accreting onto the black hole, which can launch a temporary outflow, or, in especially dramatic cases, a relativistic jet.

Aside from being cool transients (as far as spectacular stellar deaths go, they are rivaled only by the supernova), TDEs are valuable to study for a variety of reasons. They likely play a role in galaxy evolution, SMBH growth, and even the life cycles of active galactic nuclei (AGN, in which material is constantly swirling onto the SMBH). Not to mention, they are a great tool for eyeballing the mass of the SMBH responsible for the TDE; if the black hole is any bigger than about 1 billion times the mass of the Sun, its event horizon — the point at which not even light can escape its gravity — extends too far, and a star will disappear across the event horizon before it ever gets ripped apart.

How to Spot a TDE

Usually, TDEs are discovered in the X-ray (after all, not many transients are powerful enough to generate an X-ray flare) or in the optical (thanks to high-cadence, wide-field surveys like the Zwicky Transient Facility and the Legacy Survey of Space and Time). However, radio is a particularly useful regime for TDE searches, especially in dusty host galaxies where we cannot see the optical TDE signatures at all; while dust obscures optical light, the radio is unaffected! There is just one catch: how exactly can we identify a TDE based on only its radio emission?

The radio light in a TDE is generated via synchrotron radiation — which is caused by fast moving electrons in strong magnetic fields — and originates in jets or shocks. Unfortunately, this is also the case in AGN, the primary extragalactic source of variable radio emission, and it can be difficult to distinguish between the two. Additionally, the amount of light we see from synchrotron radiation at a given frequency depends on how energy is distributed among the electrons in the source, which is unknown. Perhaps the simplest case — or at least the one you’ll learn about first in your undergraduate statistical mechanics course — is that the energy is distributed among the electrons thermally (left panel in Figure 2). However, most radio transients associated with black holes are assumed to have non-thermal electron energy distributions, usually where there are exponentially many more low-energy electrons than high-energy electrons (right panel in Figure 2).

As a further challenge, very few TDEs have had extensive follow-up observations in the radio, so we don’t have strong constraints on how most TDEs should behave, especially in the long term. Luckily, some astronomers are working to change this.

This includes today’s authors, who have focused on one particular TDE, ZTF22aaajecp/AT2022cmc (I’m sure everyone mispronounces her name), or 2022cmc for short. 2022cmc is a special TDE: it is one of only five TDEs suspected to have launched a relativistic jet, and it has the highest redshift (z ~ 1.2) of the five. It was observed first in the optical and then in the X-ray and radio. The X-ray emission was highly variable for 400 days post-TDE, and then disappeared, and the first 100 days of radio emission indicated there was a relativistic outflow. At the time, it was concluded that the jet shut off and the X-ray emission ceased. However, the story doesn’t end there; the authors of today’s article continued to observe 2022cmc in the radio for an additional 900 days at frequencies spanning about 1–100 GHz.

Our authors had two key observing strategies: wide frequency coverage and long duration. Measuring the change in brightness with observing frequency, or the spectral energy distribution (SED), is important for determining which processes are responsible for the radio emission, since thermal electrons and non-thermal electrons will produce different SEDs. On the other hand, measuring the change in brightness over time, or the light curve, is important for determining what is happening at the source, such as whether there is a jet and, if so, how long it lasts. Here, our authors combine light curves at six different frequencies (Figure 3) and SEDs at nine different epochs (Figure 4) to investigate both.

The Findings

Our authors find a couple of interesting results. First, in the time domain, they find the highest-frequency light curves fade with time, while the lower-frequency light curves increase initially, hit peaks at different times (after 300 days at 15.5 GHz, and after 800 days at 1.3 GHz), and then begin to decay. The spectral evolution is even more intriguing; the SED is always peaked, and the peak shifts to lower frequencies over time, which is typical for an expanding emission region. At frequencies below the peak, the SED doesn’t change much. However, the high-frequency side of the SED shows confusing behavior: early on, it has a very steep slope (the amount of light drops off sharply at higher frequencies), but it eventually flattens.

Investigations Begin

Next, our authors consider three possibilities to explain these observations. They first consider synchrotron radiation from only non-thermal electrons in a relativistic jet (Figure 5), which is the canonical model for a gamma-ray burst radio afterglow. Initially, the jet is so fast that all its radio light is relativistically beamed in one direction (like a flashlight), and we can only see the jet if it’s pointed directly at us. Eventually, the jet slows down enough that it is no longer beamed, and light is emitted in all directions (like a light bulb). At this point, we see the light fade over time, which is exactly what happened in the high-frequency light curves. However, there is one glaring problem: this model cannot possibly explain the observed long-lasting steep SED at high frequencies. So, our authors discard this theory.

Instead, our authors consider a jetted outflow that has non-thermal and thermal electrons both independently generating synchrotron emission¹, giving us the superposition of two radio spectra. This model also doesn’t fit the data well. The peak of the SED moves too slowly, a very dense local environment is required, and, once again, the authors cannot reconcile that steep high-frequency SED.

Lastly, our authors keep the thermal/non-thermal electrons combo and ditch the jet entirely, modeling a spherical outflow. Excitingly, this model best fits the observations, and, most importantly, can explain the mysterious high-frequency behavior. Initially, most of the radio emission originates in the thermal electron population, which produces more light at higher frequencies. As the outflow expands, the non-thermal electrons begin to dominate, and the SED transforms into the classic non-thermal synchrotron shape.

Next Steps

Ideally, our authors want to compare 2022cmc to other TDEs, but few TDEs have such thorough follow-up observations. They speculate that thermal electrons were important in the radio evolution of one of the few such TDEs, Swift J1644, and recommend we revisit its emission models. More broadly, they recommend two future priorities: first, we need extensive radio observations for larger samples of TDEs, especially around 100 GHz, where the thermal electrons contribute most to the SED; secondly, we should stop neglecting thermal electrons not just in TDE models, but in models of any black hole jets, including gamma-ray bursts and X-ray binaries. While this work addresses only one event, one thing is clear. For theorists and observers alike, there is a myriad of exciting work to be done, so it’s no wonder TDEs have garnered so much attention lately.

1. A convenient property of extragalactic synchrotron sources is that all their electrons radiate independently of one another, even if they are part of the same electron population. This is called incoherent emission. (Galactic sources are another story, but I’ll save that for another time.) ︎

Original astrobite edited by Flavia Pascal.

About the author, Chloe Klare:

I’m a PhD student in astronomy and astrophysics at Penn State (with a physics minor, so I get to use my semester spent in QFT for something!). I study active galactic nuclei (in the radio!), and I’m currently looking for baby synchrotron jets in active galactic nuclei.

The post Thermal Electrons Can Explain the Mysterious Radio Behavior of a Tidal Disruption Event appeared first on AAS Nova.

Junwei Zhao et al 2026 ApJ 1004 175

More than half of solar magnetic flux appears to emerge in three bands, two of which rotate faster than the Carrington rate; this finding suggests a connection between surface flux and interior dynamical processes.

The post Long-Term Clustering Pattern of Solar Active Regions and Their Potential Connection with Magneto-Rossby Waves appeared first on AAS Nova.

A planned flagship spacecraft to Uranus was aiming to use Jupiter for a gravitational boost to shorten its journey to the outer solar system. Now that the mission’s launch date has been pushed back, it’ll need to find another way to its target.

Redesigning the Route

Uranus and Neptune, the ice giants of our solar system, have been comparatively neglected by humanity’s fleet of interplanetary probes. While all of the other major bodies have been visited by at least an orbiter or even a lander, the most detailed exploration we’ve done of these two planets happened when the Voyager 2 spacecraft went screaming past on its way toward interstellar space.

So it was no surprise when a panel of scientists and engineers charged with setting scientific exploration priorities between 2023 and 2032 recommended finally sending a spacecraft to Uranus, depositing it into orbit around the planet, and keeping it there for a while to collect data. The study itself suggested a basic design for the mission: a pair of spacecraft, one orbiter and one sacrificial atmospheric probe, collectively weighing about 4,000 kg.

Getting these spacecraft to their destination will be a challenge The thriftiest path to get to Uranus, a trajectory called a Hohmann transfer that’s been used for other missions aimed elsewhere in the solar system, would take 16–17 years. Rather than accept the long wait, the original authors suggested that the mission instead fly toward Jupiter, using the giant planet’s massive gravitational tug to slingshot the spacecraft toward Uranus.

However, this plan relied on Jupiter being in just the right place when the spacecraft approached. This in turn relied on the mission launching sometime in 2031 or 2032: any earlier or later, the slingshot would be aimed in the wrong direction. Now that timelines and budgets have slipped for this flagship mission, hitting this launch window seems unlikely. And, without the boost from Jupiter, the mission will have to cross 20 au of open interplanetary space on its own.

Solar Electric Propulsion to the Rescue

Recently, a team led by Amy Simon, NASA Goddard Space Flight Center, took on this challenge and tried to chart a new path through the solar system. The team realized that solar electric propulsion (SEP), a technique that relies on using solar panels to create electricity and accelerate ions to create thrust, might offer a path forward. By using SEP, the mission could leave Earth, unfurl wings of solar panels, then gradually accelerate for as long as there was enough sunlight to power the engine.

The power levels would likely get too low just a few astronomical units into their journey, but that would be enough: after discarding the SEP stage, the mission could coast to Uranus on a journey that would take only 13 years. Even better, this technology has a proven flight history and would require little maturation or development. The BepiColombo mission to Mercury is currently using SEP, and similar techniques are used on satellites in Earth orbit today.

Simon and collaborators also took on a number of other challenges that have cropped up since the mission was proposed, including fewer available plutonium power sources and a re-assessment of Uranus’s rings that revealed hazards in the original flight path. Their work brings the mission closer to the launch pad and illustrates how much iteration goes into the spacecraft that finally takes to the stars.

Citation

“Uranus Orbiter and Probe: Mission Challenges and Concept Updates Since the Origins, Worlds, and Life Decadal Survey,” Amy A. Simon et al 2026 Planet Sci. J. 7 143. doi:10.3847/PSJ/ae680c

The post Who Needs Jupiter? appeared first on AAS Nova.

Zhecheng Hu et al 2026 ApJS 284 70

Researchers have identified six new candidate circumbinary disk systems, potentially greatly increasing the number of known systems of this type; these system exhibit deep and prolonged dimming episodes.

The post Six New Circumbinary Disk Occultation Candidates from the Zwicky Transient Facility appeared first on AAS Nova.

Yapeng Zhang et al 2026 ApJL 1005 L29

Ultra-hot Jupiter KELT-9b possesses an outflow with a mass-loss rate above 10¹³ g s^-1 — one of the highest mass-loss rates measured for a gaseous exoplanet — and a diagnostic hydrogen Balmer line from its dayside.

The post Hydrogen Airglow from an Escaping Ultrahot Jupiter Atmosphere appeared first on AAS Nova.

While previous investigations of planet formation across the universe’s history suggest that planets trickled into the picture, a recent study has found that primordial planetesimals could have formed much earlier from the insides of the first stars in the universe.

First Stars, First Planets?

When the first stars flickered on, the universe was filled with pristine gas, containing only hydrogen, helium, and a little lithium. This gas, though great at making massive stars known as Population III (Pop III) stars, was not yet enriched with the heavy elements necessary for planet formation and, of course, life. Past studies have suggested that planet formation in the universe was gradual, taking several billion years to peak after billions of stars created and spilled the needed metals into the universe. However, local pockets of enriched gas from Pop III stars could have created the right conditions for planet formation earlier in the universe’s history.

Pop III stars burned bright and fast, exploding violently in pair-instability supernovae that completely shredded the progenitor, ejecting over 100 solar masses of metals into their previously pristine surroundings. Cosmological simulations suggest that oxygen from these supernovae could have produced significant water fractions within the dense cores of the supernova remnant. This may have set the stage for planet formation in water-rich disks around subsequent generations of stars as early as 150–200 million years after the Big Bang — does numerical modeling support this planet formation hypothesis?

Primordial Planetesimals in Simulated Water-Rich Disks

To test if these water-rich dense cores within Pop III supernova remnants could form planetesimals, the building blocks of terrestrial planets, Eduard I. Vorobyov (University of Innsbruck; Southern Federal University) and collaborators performed numerical simulations tracing the collapse of one such gas core into a protoplanetary disk around a protostar. The simulations begin from the gravitational collapse of a 1-solar-mass gas cloud core, with a protostar emerging 24 thousand years after the initial cloud collapse. As the protostar’s gravity pulled in material from its surroundings, a rotating disk formed around the growing star.

Tracking the gas and dust evolution in the disk, the authors found that several Earth masses of planetesimals formed within 0.5–1.0 au of the 0.4-solar-mass protostar. While the simulations did not trace the disk all the way to planet formation (this requires complex multi-body modeling and lots of computing power), enough planetesimals formed to create a Mars- or Earth-mass planet in the future. Luckily, unlike their live-fast and die-young predecessors, low-mass stars born from Pop III supernova remnants would still be burning hydrogen in their cores today, and ancient metal-poor stars in the Milky Way’s halo may be home to the universe’s first planets that could be detected in future exoplanet surveys. This study showed, for the first time, that water-rich protoplanetary disks with planetesimals could pop up billions of years earlier than previously thought, changing our understanding of planet formation in the universe.

Citation

“Planet Formation at Cosmic Dawn: Planetesimals in H₂O-rich Disks around Low-mass Stars,” Eduard I. Vorobyov et al 2026 ApJL 1007 L51. doi:10.3847/2041-8213/ae907c

The post Primordial Planetesimals from the Guts of Population III Stars appeared first on AAS Nova.

Asad Ukani et al 2026 ApJ 1004 171

Modeling of the Milky Way’s circumnuclear disk of molecular gas suggests that the gas is distributed in a disk with inner and outer radii of 1.0 and 2.9 parsecs and an inclination of 60 degrees.

The post Modeling the Milky Way Circumnuclear Disk: Rosettes and Rings 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: JWST Discovery of Warm Dust in the Circumgalactic Medium of the Makani Galaxy
Authors: Sylvain Veilleux et al.
First Author’s Institution: University of Maryland
Status: Published in ApJ

The Windy Galaxy

Billions of light-years away lies Makani, a record-breaking galaxy discovered in 2019 by researchers at the Keck Observatory atop Maunakea, Hawaiʻi. The galaxy shows evidence of a large merger event, where two galaxies collided to form a larger galaxy. This event triggered starburst activity, or several waves of intense star formation, that changed the makeup of not just Makani, but the region around it.

There are several processes that can create galactic winds. An active supermassive black hole at the center of the galaxy can slingshot particles out of the galaxy at close to the speed of light, or supernovae leftover from previous starburst activity can help to expel material from the galaxy. Makani, whose name in Hawaiian just so happens to mean “wind,” has both factors contributing to its galactic winds: massive amounts of star formation and a very active black hole in its center.

This contributes to some of the strongest galactic winds discovered to date, stretching approximately 100 kiloparsecs (330,000 light-years) beyond the galaxy, roughly ten times the extent of a typical galactic wind. These galactic winds remove gas from the galaxy and help to enrich the circumgalactic medium around the galaxy. There is still much to discover about how galactic winds change the makeup of such galaxies, and what exactly they take with them on their way out.

Earth’s Favorite Carcinogen: Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs, pronounced P-A-Hs or “paws”) are small flat dust grains scattered into every corner of the universe, from the atmosphere of Earth in the form of exhaust and wildfire smoke to the circumgalactic medium (the mostly empty space between galaxies). These PAHs contribute to regulating the temperature of the interstellar medium, but astronomers have long wondered how they migrate across galaxies.

Even though they are smaller than a human hair, PAHs are still easily observable even in very distant galaxies.  These dust grains emit infrared light, and if there are enough PAHs in a region, they are bright enough to be observed with modern telescopes, such as JWST. By combining multiple observations across multiple filters, astronomers can calculate ratios that reveal information about the PAHs’ size, temperature, and charge, allowing reserachers to further discern properties about the regions in which these PAHs reside.

With redshifted galaxies like Makani, the light from PAHs is stretched beyond its usual wavelength, but fortunately for today’s authors, the light was stretched just enough to land known PAH features well within JWST filters, as seen in Figure 1. The authors were then able to use this information to track the distribution of these PAHs across Makani.

PAHs Gone Extragalactic

Using JWST, the authors scrutinized Makani for any signs of PAHs. They found that not only did PAHs exist within the galaxy, these molecules were found up to 30 kpc (~100,000 light-years) outside the galaxy. Makani’s strong galactic winds were ejecting the dust grains from the galaxy over an estimated timescale of a billion years.

Previously, astronomers had not expected to find high quantities of dust grains outside the protection of a galaxy. The journey across a galaxy is long and hot, with temperatures in the millions of degrees. A dust grain would likely not survive the trip, as it would be destroyed by high-energy photons. This suggests that the PAHs were somehow shielded from the hotter parts of the interstellar medium and circumgalactic medium in large enough volumes to make it beyond the edge of Makani.

This answered questions about how galaxies enrich the circumgalactic medium, but it also added several more. Since today’s authors were limited by the sensitivity and range of their instruments, they were unable to confirm if there were PAHs along Makani’s entire wind structure, or just the first 35 kpc (114,000 light-years) of it. They also would like to turn their sights towards the intergalactic medium to see if PAHs could make it even farther beyond the reach of their host galaxy.

Original astrobite edited by Chloe Klare.

About the author, Natalie Price:

As a first-year master’s student at Wesleyan University, I study how stellar winds interact with the local interstellar medium. Outside of the observatory, you can find me dancing, with my nose in a book, or running at non-relativistic speeds.

The post Hitchhiking PAHs Caught Catching a Ride on Galactic Winds appeared first on AAS Nova.

Michelle L. Hill et al 2026 Planet. Sci. J. 7 140

Planets with radii 20% or possibly 30% smaller than Earth’s radius can maintain atmospheres, with initial carbon content, core radius fraction, initial mantle temperature, and other factors playing a role.

The post Smaller Than Earth Habitability Model (STEHM): The Lower Size Limit for Atmosphere Retention in the Habitable Zone appeared first on AAS Nova.

Aneesh Baburaj et al 2026 AJ 172 28

New observations of the coldest directly imaged planetary-mass companion of the pre-JWST era show a potential planetary formation pathway for the 25.2-Jupiter-mass object.

The post JWST-TST High Contrast: First Direct Spectroscopy of GJ 504 b Reveals Clouds and Possible Metal Enrichment appeared first on AAS Nova.

When a massive star collapses, the subsequent supernova can leave behind the star’s condensed core in the form of a neutron star. Some neutron stars are also pulsars, which rotate at incredible speeds, emit beamed radio emission, and expel winds of charged particles. A pulsar’s relativistic charged-particle winds billow around the pulsar as it travels through space — often at a few hundreds of kilometers per second or faster, having received a “kick” when its progenitor star exploded. When these winds interact with the surrounding supernova ejecta or the interstellar medium, the interaction creates a detectable pulsar wind nebula. The image above combines data from the Australian Square Kilometre Array Pathfinder (orange) and Wide-field Infrared Survey Explorer (cyan) to show a pulsar wind nebula, indicated with a white rectangle, within a larger supernova remnant. Sanja Lazarević (Western Sydney University) and collaborators discovered this pulsar wind nebula, which they’ve named “Thunder” in a nod to the supernova remnant’s moniker, “Nimbus.” The cometary shape of the pulsar wind nebula suggests that the pulsar is moving quickly, traveling outward from the center of the explosion that occurred some 30,000–45,000 years ago. To learn more about the discovery and characterization of this pulsar wind nebula, check out the article linked below.

Citation

“EMU Discovery of Thunder: A Bow-Shock PWN Powered by PSR J1631–4722 Escaping the Nimbus SNR (G336.7+0.5),” S. Lazarević et al 2026 ApJ 1007 159. doi:10.3847/1538-4357/ae7f11

The post Featured Image: A Pulsar in a Nebula in a Supernova Remnant appeared first on AAS Nova.

Astronomers have been measuring comets for centuries. But in December of last year, researchers collected a unique set of comet observations: they recorded some of the highest-quality data of one of the weirdest known comets while it was far from the Sun.

Simultaneous Spectra and Images

A few months after the famous interstellar comet 3I/ATLAS rounded the Sun and began its journey back into the space between the stars, a group of astronomers led by Nathan Roth (NASA Goddard Space Flight Center) aimed JWST in the direction of its retreat to watch it fade away. Using a special observing mode that leveraged the Integral Field Unit (IFU) in JWST’s Near Infrared Spectrometer, these observations didn’t result in just a single image of the comet, but a full stack of images, each corresponding to a different wavelength of light.

Using the IFU allowed the observers to combine the best of both regular imaging, which reveals spatial structure, and standard spectroscopy, which reveals wavelength dependencies. As a result, they could make spatially resolved maps of how the emission from the comet’s fuzzy atmosphere of gas and dust, or coma, changed with distance from the comet’s icy nucleus and angle to the Sun. Since different molecules radiate at different wavelengths, these maps in turn reveal the composition and geometry of 3I/ATLAS’s coma.

Mapping the Coma

These maps, and the spectrum created by summing all of the spatial pixels together, reveal the comet’s coma in gorgeous detail, including hundreds of individual spectral lines that can be attributed to specific molecules. These maps revealed two unique features.

First, in contrast with normal solar system comets where water is the most abundant molecule, water was actually a secondary player here: there was significantly more carbon monoxide, or CO, than water in 3I/ATLAS’s coma. The researchers note that this might not be representative of the true distribution of the two species, but instead be the result of the timing of these observations. When observing a standard solar system comet, astronomers usually examine their targets when the object in question is within 2 au of the Sun. At these close distances, solar radiation is strong enough that water ice dominates the outgassing and activity in a coma.

However, these IFU measurements were taken when 3I/ATLAS was about 2.4 au from the Sun, or right in the transition region where water doesn’t sublimate as easily as CO or carbon dioxide (CO₂). It’s likely that as the comet approaches the so-called “ice line” where water will naturally freeze out, CO will only increase its domination of the coma.

Every Molecule for Itself

Second, each molecule seemed to be outgassing in its own unique direction from the coma. CO is leaving the nucleus in two different jets, one aimed directly back at the Sun and one perpendicular to it; CO₂ and methane (CH₄) are both leaking away in the anti-Sun direction; and water and methanol (CH₃OH) are sublimating in nearly spherically symmetric shells. The authors speculate that these geometries may be caused by different “active sites” on the comet, and that had they observed the comet for one full rotational period, they might have seen these jets pointing in different directions.

Although 3I/ATLAS is now too far and faint for observations like these, this study reveals just how much we can learn in the brief time interstellar visitors spend in our solar system. When the fourth interstellar comet inevitably wanders through the inner solar system, astronomers will doubtless be ready to use this observing mode again.

Citation

The post An Interstellar Comet’s Coma Composition appeared first on AAS Nova.

Itai Sfaradi et al 2026 ApJL 1005 L19

Recent radio rebrightening of a supernova observed in 2012 suggests that either the progenitor star experienced a past change in mass-loss rate or wind speed, or there is an off-axis relativistic jet present.

The post A 14-Yr-Old Mystery: The Peculiar Case of the Engine-Driven SN 2012ap appeared first on AAS Nova.

Ádám Mátéfy et al 2026 ApJ 1004 142

Gaia21bja is a young stellar object that brightens by up to 1.7 magnitudes during its outbursts, with its luminosity and mass-accretion rate increasing by a factor of 5.5–6 during the bursts.

The post Gaia21bja: Pre-Main-Sequence Star with Quasiperiodic Bursts appeared first on AAS Nova.

Yunshi Zeng et al 2026 ApJS 284 63

Using more than 50,000 images of coronal mass ejections, researchers have developed a novel machine-learning classification framework applicable to coronal mass ejections.

The post Automatic Detection and Segmentation of Coronal Mass Ejections in LASCO C3 Images appeared first on AAS Nova.

New research suggests that the circumplanetary disk surrounding the exoplanet PDS 70c contains a ring of dense dust, and the conditions within this ring may allow baby moons to form.

A Disk Within a Disk

The young star PDS 70 has become famous for its protoplanetary disk and its two growing giant planets, PDS 70b and PDS 70c. At least one of these planets is surrounded by a disk of its own; in 2019, researchers using the Atacama Large Millimeter/submillimeter Array (ALMA) reported the first-ever observation of a circumplanetary disk around PDS 70c, and later observations with ALMA brought clearer views of this disk.

There’s still debate over the exact source of the emission detected by ALMA. Does this emission come from dust, and if so, how is the dust distributed? Is the disk optically thick or optically thin? Does the emission even come from dust, or could it instead be free–free emission from unbound electrons navigating a charged-particle maze?

Dust Diagnosis

Yuhito Shibaike (Kagoshima University) and collaborators recently examined the hypothesis that the emission from PDS 70c’s circumplanetary disk arises from dust distributed in an optically thick ring. To test this hypothesis, the team explored two possible dust distributions, which they call “drift” and “ring.” In the drift model, dust grains within the circumplanetary disk migrate inward toward the planet, leaving much of the disk optically thin. Modeling suggests that this migration is typical in protoplanetary disks, and it might be common in circumplanetary disks as well.

In the ring model, the dust grains are concentrated within an optically thick ring at a certain distance from the planet. Simulations suggest that the formation of this type of dust ring is feasible, arising from a localized increase in gas density, outflows, or other causes.

Shibaike and coauthors found that the ring model naturally reproduced the observed spectral energy distribution for a range of reasonable parameters. The drift model, on the other hand, required an unrealistically high dust-to-gas ratio for the material accreted onto the circumplanetary disk from the parent protoplanetary disk to reproduce the observed spectral index.

Future Prospects and Moon-Making Possibilities

This work demonstrated the feasibility of the dust-ring model, but it didn’t rule out a contribution due to free–free emission from unbound electrons, which has also been proposed to explain the disk’s appearance. The team noted that distinguishing between thermal dust emission and free–free emission is challenging with existing data, as the two sources produce spectral energy distributions with similar shapes.

Luckily, this likely won’t remain a mystery forever: the next-generation Very Large Array, which is anticipated to begin full science operations in the mid-2030s, should be able to resolve the location of the dust within the circumplanetary disk and illuminate the source of emission.

Finally, if the dust surrounding PDS 70c is concentrated within a ring, what does that mean for the possibility of moons forming within the disk? Shibaike and collaborators found that the conditions within the ring likely satisfy the requirements of both the streaming instability and the gravitational instability, which are required for dust grains to clump together and form the rocky building blocks of baby moons. Perhaps the PDS 70 system will one day be the site of not only a circumplanetary disk, but an exomoon as well!

Citation

“Interpreting ALMA Multiwavelength Continuum Observations of PDS 70 c: An Optically Thick Dust Ring in the Circumplanetary Disk,” Yuhito Shibaike et al 2026 ApJL 1006 L26. doi:10.3847/2041-8213/ae86f5

The post Probing Dust in the Disk of a Growing Giant Planet appeared first on AAS Nova.

Sandeep Kumar et al 2026 ApJ 1006 26

By combining ground-based and space-based solar observations, researchers found that solar minimum solar wind predictions require higher source-surface heights than solar maximum predictions.

The post Source Surface Height Optimization for Improved Solar Wind Velocity Forecasting Across Solar Cycles 23, 24, and 25 appeared first on AAS Nova.