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1. Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes

   https://doi.org/10.3847/1538-4357/accd5d  

   Plummer, Michael K.; Wang 王, Ji 吉 (July 2023, The Astrophysical Journal)

   Abstract Extremely large telescopes (ELTs) present an unparalleled opportunity to study the magnetism, atmospheric dynamics, and chemistry of very-low-mass (VLM) stars, brown dwarfs, and exoplanets. Instruments such as the Giant Magellan Telescope–Consortium Large Earth Finder (GMT/GCLEF), the Thirty Meter Telescope’s Multi-Objective Diffraction-limited High-Resolution Infrared Spectrograph (TMT/MODHIS), and the European Southern Observatory’s Mid-Infrared ELT Imager and Spectrograph (ELT/METIS) provide the spectral resolution and signal-to-noise ratio necessary to Doppler image ultracool targets’ surfaces based on temporal spectral variations due to surface inhomogeneities. Using our publicly available code,Imber, developed and validated in Plummer & Wang, we evaluate these instruments’ abilities to discern magnetic starspots and cloud systems on a VLM star (TRAPPIST-1), two L/T transition ultracool dwarfs (VHS J1256−1257 b and SIMP J0136+0933), and three exoplanets (Beta Pic b and HR 8799 d and e). We find that TMT/MODHIS and ELT/METIS are suitable for Doppler imaging the ultracool dwarfs and Beta Pic b over a single rotation. Uncertainties for longitude and radius are typically ≲10°, and latitude uncertainties range from ∼10° to 30°. TRAPPIST-1's edge-on inclination and low $\upsilon \sin i$provide a challenge for all three instruments, while GMT/GCLEF and the HR 8799 planets may require observations over multiple rotations. We compare the spectroscopic technique, photometry-only inference, and the combination of the two. We find combining spectroscopic and photometric observations can lead to improved Bayesian inference of surface inhomogeneities and offers insight into whether ultracool atmospheres are dominated by spotted or banded features. 

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2. Evidence for a Volcanic Atmosphere on the Sub-Earth L 98-59 b

   https://doi.org/10.3847/2041-8213/adaf22  

   Bello-Arufe, Aaron; Damiano, Mario; Bennett, Katherine A; Hu, Renyu; Welbanks, Luis; MacDonald, Ryan J; Seligman, Darryl Z; Sing, David K; Tokadjian, Armen; Oza, Apurva V; et al (February 2025, The Astrophysical Journal Letters)

   Abstract Assessing the prevalence of atmospheres on rocky planets around M-dwarf stars is a top priority of exoplanet science. High-energy activity from M dwarfs can destroy the atmospheres of these planets, which could explain the lack of atmosphere detections to date. Volcanic outgassing has been proposed as a mechanism to replenish the atmospheres of tidally heated rocky planets. L 98-59 b, a sub-Earth transiting a nearby M dwarf, was recently identified as the most promising exoplanet to detect a volcanic atmosphere. We present the transmission spectrum of L 98-59 b from four transits observed with JWST NIRSpec G395H. Although the airless model provides an adequate fit to the data based on itsχ², an SO₂atmosphere is preferred by 3.6σover a flat line in terms of the Bayesian evidence. Such an atmosphere would likely be in a steady state where volcanism balances escape. If so, L 98-59 b must experience at least eight times as much volcanism and tidal heating per unit mass as Io. If volcanism is driven by runaway melting of the mantle, we predict the existence of a subsurface magma ocean in L 98-59 b extending up toR_p ∼  60%–90%. An SO₂-rich volcanic atmosphere on L 98-59 b would be indicative of an oxidized mantle with an oxygen fugacity offO₂ > IW + 2.7, and it would imply that L 98-59 b must have retained some of its volatile endowment despite its proximity to its star. Our findings suggest that volcanism may revive secondary atmospheres on tidally heated rocky planets around M dwarfs. 

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3. Early Results from the HUMDRUM Survey: A Small, Earth-mass Planet Orbits TOI-1450A

   https://doi.org/10.3847/1538-3881/ad500a  

   Brady, Madison; Bean, Jacob L; Seifahrt, Andreas; Kasper, David; Luque, Rafael; Stefánsson, Guđmundur; Stürmer, Julian; Charbonneau, David; Collins, Karen A; Doty, John P; et al (July 2024, The Astronomical Journal)

   Abstract M-dwarf stars provide us with an ideal opportunity to study nearby small planets. The HUnting for M Dwarf Rocky planets Using MAROON-X (HUMDRUM) survey uses the MAROON-X spectrograph, which is ideally suited to studying these stars, to measure precise masses of a volume-limited (<30 pc) sample of transiting M-dwarf planets. TOI-1450 is a nearby (22.5 pc) binary system containing a M3 dwarf with a roughly 3000 K companion. Its primary star, TOI-1450A, was identified by the Transiting Exoplanet Survey Satellite (TESS) to have a 2.04 days transit signal, and is included in the HUMDRUM sample. In this paper, we present MAROON-X radial velocities (RVs) which confirm the planetary nature of this signal and measure its mass at nearly 10% precision. The 2.04 days planet, TOI-1450A b, hasR_b= 1.13 ± 0.04R_⊕andM_b= 1.26 ± 0.13M_⊕. It is the second-lowest-mass transiting planet with a high-precision RV mass measurement. With this mass and radius, the planet’s mean density is compatible with an Earth-like composition. Given its short orbital period and slightly sub-Earth density, it may be amenable to JWST follow-up to test whether the planet has retained an atmosphere despite extreme heating from the nearby star. We also discover a nontransiting planet in the system with a period of 5.07 days and a $M\sin i_c=1.53\pm 0.18M_{\oplus }$. We also find a 2.01 days signal present in the systems’s TESS photometry that likely corresponds to the rotation period of TOI-1450A’s binary companion, TOI-1450B. TOI-1450A, meanwhile, appears to have a rotation period of approximately 40 days, which is in line with our expectations for a mid-M dwarf. 

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4. Constraining the Thickness of TRAPPIST-1 b’s Atmosphere from Its JWST Secondary Eclipse Observation at 15 μm

   https://doi.org/10.3847/2041-8213/ace03b  

   Ih, Jegug; Kempton, Eliza M.-R.; Whittaker, Emily A.; Lessard, Madeline (July 2023, The Astrophysical Journal Letters)

   Abstract Recently, the first JWST measurement of thermal emission from a rocky exoplanet was reported. The inferred dayside brightness temperature of TRAPPIST-1 b at 15 μ m is consistent with the planet having no atmosphere and therefore no mechanism by which to circulate heat to its nightside. In this Letter, we compare TRAPPIST-1 b's measured secondary eclipse depth to predictions from a suite of self-consistent radiative-convective equilibrium models in order to quantify the maximum atmospheric thickness consistent with the observation. We find that plausible atmospheres (i.e., those that contain at least 100 ppm CO 2 ) with surface pressures greater than 0.3 bar are ruled out at 3 σ , regardless of the choice of background atmosphere, and a Mars-like thin atmosphere with surface pressure 6.5 mbar composed entirely of CO 2 is also ruled out at 3 σ . Thicker atmospheres of up to 10 bar (100 bar) are consistent with the data at 1 σ (3 σ ) only if the atmosphere lacks any strong absorbers across the mid-IR wavelength range—a scenario that we deem unlikely. We additionally model the emission spectra for bare-rock planets of various compositions. We find that a basaltic, metal-rich, and Fe-oxidized surface best matches the measured eclipse depth to within 1 σ , and the best-fit gray albedo is 0.02 ± 0.11. We conclude that planned secondary eclipse observations at 12.8 μ m will serve to validate TRAPPIST-1 b's high observed brightness temperature, but are unlikely to further distinguish among the consistent atmospheric and bare-rock scenarios. 

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5. Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

   https://doi.org/10.1038/s41586-022-05677-y  

   Rustamkulov, Z; Sing, D K; Mukherjee, S; May, E M; Kirk, J; Schlawin, E; Line, M R; Piaulet, C; Carter, A L; Batalha, N E; et al (February 2023, Nature)

   Abstract Transmission spectroscopy^1–3of exoplanets has revealed signatures of water vapour, aerosols and alkali metals in a few dozen exoplanet atmospheres^4,5. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations’ relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species—in particular the primary carbon-bearing molecules^6,7. Here we report a broad-wavelength 0.5–5.5 µm atmospheric transmission spectrum of WASP-39b⁸, a 1,200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with the JWST NIRSpec’s PRISM mode⁹as part of the JWST Transiting Exoplanet Community Early Release Science Team Program^10–12. We robustly detect several chemical species at high significance, including Na (19σ), H₂O (33σ), CO₂(28σ) and CO (7σ). The non-detection of CH₄, combined with a strong CO₂feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4 µm is best explained by SO₂(2.7σ), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST’s sensitivity to a rich diversity of exoplanet compositions and chemical processes. 

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