Study Findings: TESS Planet Occurrence Rates Reveal the Disappearance of the Radius Valley around Mid-to-late M Dwarfs

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Image (Credit): Artist’s rendering of NASA’s Transiting Exoplanet Survey Satellite (TESS). (NASA)

The Astronomical Journal abstract of study findings:

We present the deepest systematic search for planets around mid-to-late M dwarfs to date. We have surveyed 8134 mid-to-late M dwarfs observed by the Transiting Exoplanet Survey Satellite with a custom-built pipeline and recover 77 vetted transiting planet candidates. We characterize the sensitivity of our survey via injection–recovery and measure the occurrence rate of planets as a function of orbital period, instellation, and planet radius. We measure a cumulative occurrence rate of 1.10 ± 0.16 planets per star with radii >1 R⊕ orbiting within 30 days. This value is consistent with the cumulative occurrence rate around early M dwarfs, making M dwarfs collectively the most prolific hosts of small close-in planets. Unlike the bimodal radius valley exhibited by close-in planet populations around FGK and early M dwarfs, we recover a unimodal planet radius distribution peaking at 1.25 ± 0.05 R⊕. We additionally find 0.954 ± 0.147 super-Earths and 0.148 ± 0.045 sub-Neptunes per star, with super-Earths outnumbering sub-Neptunes 5.5:1, firmly demonstrating that the radius valley disappears around the lowest-mass stars. The dearth of sub-Neptunes around mid-to-late M dwarfs is consistent with predictions from water-rich pebble accretion models that predict a fading radius valley with decreasing stellar mass. Our results support the emerging idea that the sub-Neptune population around M dwarfs is composed of water-rich worlds. We find no hot Jupiters in our survey and set an upper limit of 0.012 hot Jupiters per mid-to-late M dwarf within 10 days.

Citation: Erik Diego Gillis et al. TESS planet occurrence rates reveal the disappearance of the radius valley around mid-to-late M dwarfs. AJ 171 317 (2026).

DOI: https://doi.org/10.3847/1538-3881/ae5810

Study-related stories:

Phys.org – “The Most Common Planets in the Galaxy Don’t Appear Around the Most Common Stars, TESS Observations Suggest”

Newsbreak – “TESS Uncovers Cosmic Surprise: Galaxy’s Most Common Planets Skip Its Most Common Star”

Universe Today – “Closing The Exoplanet Radius Gap”

Study Findings: Detection of an Atmosphere on a Trans-Neptunian Object Beyond Pluto

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Image (Credit): An artist’s rendering of NASA’s New Horizons spacecraft approaching Pluto with its largest moon Charon in the background. (NASA’s Goddard Space Flight Center/The Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

Nature Astronomy abstract of study findings:

The only trans-Neptunioan object (TNO) with a detected atmosphere so far is Pluto, which has an average surface pressure of 10 μbar. Investigations of other large (>500 km) TNOs have only been able to establish upper limits of 1–100 nbar. A recent near-infrared study reported methane gas emission from Makemake, although its origin remains uncertain. Here we report that a stellar occultation campaign performed on 10 January 2024 of the ~250-km-radius plutino (612533) 2002 XV93 reveals a refractive signature, indicating a thin atmosphere. We derive a surface pressure of 100–200 nbar, above the previous limits for other larger bodies. This discovery shows that even a few-hundred-kilometre TNO can host, at least transiently, an atmosphere, challenging standard volatile-retention scenarios. Our findings suggest that a fraction of distant icy minor planets can exhibit atmospheres, potentially sustained by ongoing cryovolcanic activity or produced by a recent impact of a small icy object.

Citation: Arimatsu, K., Yoshida, F., Hayamizu, T. et al. Detection of an atmosphere on a trans-Neptunian object beyond Pluto. Nat Astron (2026).

DOI: https://doi.org/10.1038/s41550-026-02846-1

Study-related stories:

CNN – “Astronomers Find Atmosphere Around a Solar System Object that Shouldn’t Have One”

Science News – “A Small Object Past Pluto May Have a Thin Atmosphere”

The Japan Times– “Japan Astronomers Find Thin Atmosphere on Small Celestial Body Beyond Neptune”

Study Findings: A Second Visit to Eps Ind Ab with JWST: New Photometry Confirms Ammonia and Suggests Thick Clouds in the Exoplanet Atmosphere of the Closest Super-Jupiter

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Image (Credit): Juno mission image of Jupiter taken on Juno’s 22nd close pass by Jupiter on Sept. 12, 2019. (NASA/JPL-Caltech/SwRI/MSSS / Image processing by Prateek Sarpal, © CC NC SA)

The Astrophysical Journal Letters abstract of study findings:

With JWST, we are directly imaging cold (∼200–300 K) solar-age giant exoplanets for the first time. At these temperatures, many molecular features appear, and water-ice clouds may condense and affect the emission spectrum; early photometric measurements of cold giant planets are already showing some tension with the predictions of cloud-free solar-metallicity atmosphere models. Here, we present new JWST/MIRI coronagraphic observations of the cold giant exoplanet Eps Ind Ab at 11.3 μm. Together with archival data, we use these new observations to study the atmosphere of this cold exoplanet, and we also refit its orbit, finding an updated mass of 7.6  ±  0.7MJup and an eccentricity of 0.24 +0.11/-0.08. The planet is significantly brighter (by 0.88  ±  0.08 mag) at 11.3 μm than at 10.6 μm, indicating the presence of ammonia. However, this ammonia feature is shallower than expected. This could indicate a low-metallicity or nitrogen-depleted atmosphere, but our preferred explanation is the presence of thick water-ice clouds that suppress the ammonia feature and the near-IR emission of Eps Ind Ab. Photometry of the small but growing sample of cold giant exoplanets demonstrates that they are consistently fainter than expected between 3 and 5 μm, consistent with the water-ice cloud hypothesis. 10.6 μm and 11.3 μm photometry of this cold exoplanet sample would be valuable to determine whether the suppressed ammonia feature is universal, and to frame a new open question about the underlying physical cause.

Citation: Elisabeth C. Matthews et al. a second visit to eps ind ab with JWST: new photometry confirms ammonia and suggests thick clouds in the exoplanet atmosphere of the closest super-Jupiter, ApJL 1002 L5 (2026).

DOI: 10.3847/2041-8213/ae5823

Study-related stories:

Max Planck Institute for Astronomy – “Cirrus Clouds Made of Water Ice May Surround a Jupiter-like Exoplanet”

Universe Today – “Webb Finds Water-Ice Clouds on Nearby Super-Jupiter”

Sci.News – “Webb Spots Icy Clouds on Distant Jupiter-Like Exoplane”

Study Findings: An Adolescent and Near-resonant Planetary System Near the End of Photoevaporation

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Credit: Image by Adis Resic from Pixabay

Nature Astronomy abstract of study findings:

Young exoplanets provide vital insights into the early dynamical and atmospheric evolution of planetary systems. Many multi-planet systems younger than 100 Myr exhibit mean-motion resonances, probably established through convergent disk migration. Over time, however, these resonant chains are often disrupted, mirroring the Nice model proposed for the Solar System. Here we present a detailed characterization of the ~200-Myr-old TOI-2076 system, which contains four sub-Neptune planets between 1.4 and 3.5 Earth radii. We demonstrate that its planets are near to but not locked in mean-motion resonances, making the system dynamically fragile. The four planets have comparable core masses but display a monotonic increase in hydrogen and helium (H/He) envelope mass fractions (from stripped to 1%, 5% and 5%) with decreasing stellar insolation. This trend is consistent with atmospheric mass loss due to photoevaporation, which predicts that the envelopes of irradiated planets either erode completely or stabilize at a residual level of ~1% by mass within the first few hundred million years, with more distant, less-irradiated planets retaining most of their primordial envelopes. Additionally, previous detections of metastable helium outflows rule out a pure water-world scenario for the TOI-2076 planets. Our finding provides direct observational evidence that the dynamical and atmospheric reshaping of compact planetary systems begins early and offers an empirical anchor for models of their long-term evolution.

Citation: Wang, MT., Dai, F., Liu, HG. et al. An adolescent and near-resonant planetary system near the end of photoevaporation, Nat Astron (2026).

https://doi.org/10.1038/s41550-026-02795-9

Study-related stories:

Florida Tech – “Assessment of Rare Teenage Planetary System Deepens Understanding of Cosmic Evolution”

Universe Today – “Adolescence Is Tumultuous, Even For Exoplanets”

Daily Galaxy – “Scientists Discover ‘Teenage’ Planetary System, Unlocking Secrets of Cosmic Growth”

Study Findings: Building Wet Planets Through High-Pressure Magma–Hydrogen Reactions

Posted on by onespaceman2000
Credit: Image by Yol Gezer from Pixabay

Nature abstract of study findings:

Close-in transiting sub-Neptunes are abundant in our Galaxy. Planetary interior models based on their observed radius–mass relationship suggest that sub-Neptunes contain a discernible amount of either hydrogen (dry planets) or water (wet planets) blanketing a core composed of rocks and metal. Water-rich sub-Neptunes have been believed to form farther from the star and then migrate inwards to their present orbits. Here we report experimental evidence of reactions between warm, dense hydrogen fluid and silicate melt that release silicon from the magma to form alloys and hydrides at high pressures. We found that oxygen liberated from the silicate melt reacts with hydrogen, producing an appreciable amount of water up to a few tens of weight per cent, which is much greater than previously predicted based on low-pressure ideal gas extrapolation. Consequently, these reactions can generate a spectrum of water contents in hydrogen-rich planets, with the potential to reach water-rich compositions for some sub-Neptunes, implying an evolutionary relationship between hydrogen-rich and water-rich planets. Therefore, detection of a large amount of water in exoplanet atmospheres may not be the optimal evidence for planet migration in the protoplanetary disk, calling into question the assumed link between composition and planet formation location.

Citation: Horn, H.W., Vazan, A., Chariton, S. et al. Building wet planets through high-pressure magma–hydrogen reactions. Nature 646, 1069–1074 (2025).

https://doi.org/10.1038/s41586-025-09630-7

Study-related stories:

Science News – “Some Planets Might Home Brew their Own Water”

Universe Today – “Some Exoplanets Can Create Their Own Water Through Crust-Atmosphere Reactions”

Space Daily – “Water Production on Exoplanets Revealed by Pressure Experiments”