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.

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.

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.

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.

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.

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.

The supernova remnant W50 — nicknamed “the Manatee” because its blobby radio emission resembles an aquatic mammal floating through starry waters — harbors an extreme system at its heart. Near the center of the remnant, the microquasar SS 433 exhibits an immense pair of relativistic jets, likely powered by a stellar-mass black hole accreting material from a companion star. In the image of W50/SS 433 above, radio emission is in red, optical light is in yellow, and soft, medium, and hard X-ray emission are in green, cyan, and magenta, respectively. Brydyn Mac Intyre (University of Manitoba) and collaborators focused on the region circled above, using NuSTAR and XMM-Newton to understand the source of the X-ray emission in that region and the potential for SS 433 to accelerate particles to relativistic velocities. These observations suggest that W50/SS 433 accelerates electrons up to energies of more than 100 teraelectronvolts, and it may launch other particles into the highly sought-after petaelectronvolt range. To learn more about the particle-acceleration possibilities in this remarkable region, be sure to check out the full research article linked below.

Citation

“The Western Jet of SS 433/W50: Hard X-Ray Emission, Spectral Evolution, and Comparison to the Eastern Jet,” Brydyn Mac Intyre et al 2026 ApJ 1006 69. doi:10.3847/1538-4357/ae7a47

The post Featured Image: The Microquasar and the Manatee appeared first on AAS Nova.

Yejing Zhan et al 2026 ApJL 1004 L46

The combination of gravitational wave emission, magnetic dissipation, and tidal interactions should cause the beat clock period of the CHIME/ILT J1634+44 system to change by tens of seconds per year.

The post A Falsifiable Timing Test for the Double-White-Dwarf Model of Long-Period Transients appeared first on AAS Nova.

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The post ALMA-QUARKS View of W49N: Multipolar Episodic Outflow Associated with the Most Energetic Galactic Water Maser appeared first on AAS Nova.

Ultra-hot Jupiter WASP-121b is once again puzzling astronomers. New JWST observations have revealed aspects of this superheated planet’s atmosphere that models cannot yet explain.

An Extreme Planet

Among the more than 6,000 known exoplanets, there are many types of worlds that aren’t represented in our solar system. The most exotic and unfamiliar planets might be the ultra-hot Jupiters: giant planets nestled so close to their host stars that they are tidally locked, with temperatures on their permanently starlit sides climbing to thousands of degrees.

WASP-121b, which circles its F-dwarf host star every 30.5 hours, is one of the best-studied ultra-hot Jupiters. Previous work has started to reveal the complexity of its atmosphere, and now, data from JWST have opened a new window onto WASP-121b’s behavior.

New View from JWST

To learn more about WASP-121b’s atmosphere, Robert C. Frazier (University of Michigan) and collaborators analyzed JWST Near Infrared Imager and Slitless Spectrograph (NIRISS) observations covering more than one full orbit of the planet. These observations allowed them to construct the system’s phase curve, which describes the total amount of emitted and reflected light from the planet and its host star over an entire orbit.

The team used two 3D general circulation models to predict the planet’s atmospheric structure and extract synthetic spectra and phase curves to compare against the JWST observations. Using nine model configurations in total, the team varied several inputs, including sources of atmospheric opacity, sources of atmospheric drag, and assumptions about whether clouds are able to form on the planet’s cooler nightside.

Left with a Mystery

Frazier and collaborators found two aspects of WASP-121b’s phase curve that their models couldn’t explain: the planet emits less light overall than predicted, and the location of its phase-curve offset changes with wavelength.

The models predict, on average, 12–15% more emission from the planet than observed. This discrepancy might be traced back to how the planet’s radius is determined, which is a simple-sounding task that can be deceptively difficult; WASP-121b isn’t perfectly spherical, and its emitting area changes with wavelength, making it challenging to normalize the planet’s radius for use in models.

The phase-curve offset is the difference between a planet’s sub-stellar point (where the star is directly overhead) and the brightest point in the planet’s atmosphere. In general, some degree of offset is expected because planetary winds tend to whisk heat away from the sub-stellar point, placing the brightest point somewhere to the east (usually). For WASP-121b, the offset is unexpectedly small — suggesting a source of drag in the atmosphere that prevents winds from transporting heat away from the sub-stellar point — and it’s larger at shorter wavelengths. This wavelength dependence isn’t predicted by any of the models, and it’s not clear what causes it.

These results demonstrate something remarkable: that our observations of a planet nearly 900 light-years away have become so precise that they’re pushing our already complex models to include more physics — an exceptionally exciting motivation for model improvement!

Citation

“The Days Drag On on WASP-121 b: Interpreting Its NIRISS Spectroscopic Phase Curve with General Circulation Models,” Robert C. Frazier et al 2026 ApJ 1004 102. doi:10.3847/1538-4357/ae69ca

The post Complexities and Mysteries in the Atmosphere of Ultra-Hot Jupiter WASP-121b appeared first on AAS Nova.

The post X-Ray Spectroscopy Mass Constraints on V1674 Her: The Fastest Nova Does Not have a Near-Chandrasekhar White Dwarf appeared first on AAS Nova.