Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d
The Astrophysical Journal American Astronomical Society 989:2 (2025) 181
Abstract:
The nearby TRAPPIST-1 system, with its seven small rocky planets orbiting a late-type M8 star, offers an unprecedented opportunity to search for secondary atmospheres on temperate terrestrial worlds. In particular, the 0.8 R⊕TRAPPIST-1 d lies at the edge of the habitable zone (Teq,A=0.3 = 262 K). Here we present the first 0.6–5.2 μm NIRSpec/PRISM transmission spectrum of TRAPPIST-1 d from two transits with JWST. We find that stellar contamination from unocculted bright heterogeneities introduces 500–1000 ppm visit-dependent slopes, consistent with constraints from the out-of-transit stellar spectrum. Once corrected, the transmission spectrum is flat within ±100–150 ppm, showing no evidence for a haze-like slope or molecular absorption despite NIRSpec/PRISM’s sensitivity to CH4, H2O, CO, SO2, and CO2. Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (>3σ). We leverage our constraints on even trace amounts of CH4, H2O, and CO2 to further reject high mean molecular weight compositions analogous to a haze-free Titan, a cloud-free Venus, early Mars, and both Archean Earth and a cloud-free modern Earth scenario (>95% confidence). If TRAPPIST-1 d retains an atmosphere, it is likely extremely thin or contains high-altitude aerosols, with water cloud formation at the terminator predicted by 3D global climate models. Alternatively, if TRAPPIST-1 d is airless, our evolutionary models indicate that TRAPPIST-1 b, c, and d must have formed with ≲4 Earth oceans of water, though this would not preclude atmospheres on the cooler habitable-zone planets TRAPPIST-1 e, f, and g.JWST NIRISS transmission spectroscopy of the super-Earth GJ 357b, a favourable target for atmospheric retention
Monthly Notices of the Royal Astronomical Society Oxford University Press 540:4 (2025) 3677-3692
Abstract:
We present a JWST Near Infrared Imager and Slitless Spectrograph/Single Object Slitless Spectroscopy transmission spectrum of the super-Earth GJ 357 b: the first atmospheric observation of this exoplanet. Despite missing the first 40 per cent of the transit due to using an out-of-date ephemeris, we still recover a transmission spectrum that does not display any clear signs of atmospheric features. We perform a search for Gaussian-shaped absorption features within the data but find that this analysis yields comparable fits to the observations as a flat line. We compare the transmission spectrum to a grid of atmosphere models and reject, to 3 confidence, atmospheres with metallicities solar (4 g mol−1) with clouds at pressures down to 0.01 bar. We analyse how the retention of a secondary atmosphere on GJ 357 b may be possible due to its higher escape velocity compared to an Earth-sized planet and the exceptional inactivity of its host star relative to other M2.5V stars. The star’s XUV luminosity decays below the threshold for rapid atmospheric escape early enough that the volcanic revival of an atmosphere of several bars of CO is plausible, though subject to considerable uncertainty. Finally, we model the feasibility of detecting an atmosphere on GJ 357 b with MIRI/LRS, MIRI photometry, and NIRSpec/G395H. We find that, with two eclipses, it would be possible to detect features indicative of an atmosphere or surface. Further to this, with three to four transits, it would be possible to detect a 1 bar nitrogen-rich atmosphere with 1000 ppm of CO.SiO and a super-stellar C/O ratio in the atmosphere of the giant exoplanet WASP-121 b
Nature Astronomy Nature Research 9:6 (2025) 845-861
Abstract:
Refractory elements such as iron, magnesium and silicon can be detected in the atmospheres of ultrahot giant planets. This provides an opportunity to quantify the amount of refractory material accreted during formation, along with volatile gases and ices. However, simultaneous detections of refractories and volatiles have proved challenging, as the most prominent spectral features of associated atoms and molecules span a broad wavelength range. Here, using a single JWST observation of the ultrahot giant planet WASP-121 b, we report detections of H2O (5.5–13.5σ), CO (10.8–12.8σ) and SiO (5.7–6.2σ) in the planet’s dayside atmosphere and CH4 (3.1–5.1σ) in the nightside atmosphere. We measure super-stellar values for the atmospheric C/H, O/H, Si/H and C/O ratios, which point to the joint importance of pebbles and planetesimals in giant planet formation. The CH4-rich nightside composition is also indicative of dynamical processes, such as strong vertical mixing, having a profound influence on the chemistry of ultrahot giant planets.JWST NIRISS Transmission Spectroscopy of the Super-Earth GJ 357b, a Favourable Target for Atmospheric Retention
(2025)
A Moderate Albedo from Reflecting Aerosols on the Dayside of WASP-80 b Revealed by JWST/NIRISS Eclipse Spectroscopy
Astronomical Journal American Astronomical Society 169:5 (2025) 277