Limits on the atmospheric metallicity and aerosols of the sub-Neptune GJ 3090 b from high-resolution CRIRES+ spectroscopy
Monthly Notices of the Royal Astronomical Society, Volume 538, Issue 4, pp.3263-3283
Abstract:
The sub-Neptune planets have no solar system analogues, and their low bulk densities suggest thick atmospheres containing degenerate quantities of volatiles and H/He, surrounding cores of unknown sizes. Measurements of their atmospheric composition can help break these degeneracies, but many previous studies at low spectral resolution have largely been hindered by clouds or hazes, returning muted spectra. Here, we present the first comprehensive study of a short-period sub-Neptune using ground-based, high-resolution spectroscopy, which is sensitive to the cores of spectral lines that can extend above potential high altitude aerosol layers. We observe four CRIRES+ K-band transits of the warm sub-Neptune GJ 3090 b (T eq = 693 卤 18 K) which orbits an M2V host star. Despite the high quality data and sensitivity to CH4, H2O, NH3, and H2S, we detect no molecular species. Injection-recovery tests are consistent with two degenerate scenarios. First, GJ 3090 b may host a highly metal-enriched atmosphere with > 150 Z 鈯 and mean molecular weight > 7.1 g mol 鈭1, representing a volatile dominated envelope with a H/He mass fraction xH/He<33 per cent, and an unconstrained aerosol layer. Second, the data are consistent with a high altitude cloud or haze layer at pressures < 3.3 脳10鈭5 bar, for any metallicity. GJ 3090 b joins the growing evidence to suggest that high metallicity atmospheres and high altitude aerosol layers are common within the warm (500 < Teq < 800 K) sub-Neptune population. We discuss the observational challenges posed by the M-dwarf host star, and suggest observing strategies for transmission spectroscopy of challenging targets around M-dwarfs for existing and ELT instrumentation.
Modeling Atmospheric Ion Escape from Kepler-1649 b and c over Time
The Astrophysical Journal Letters, Volume 994, Number 2, L50 (2025)
Abstract:
Rocky planets orbiting M dwarf stars are prime targets for atmospheric characterization, yet their long-term evolution under intense stellar winds and high-energy radiation remains poorly constrained. The Kepler-1649 system, hosting two terrestrial exoplanets orbiting an M5V star, provides a valuable laboratory for studying atmospheric evolution in the extreme environments typical of M dwarf systems. In this Letter, we show that both planets could have retained atmospheres over gigayear timescales. Using a multispecies magnetohydrodynamic model, we simulate atmospheric ion escape driven by stellar winds and extreme-ultraviolet radiation from 0.8 to 4.0 Gyr. The results reveal a clear decline in total ion escape rates with stellar age, as captured by a nonparametric LOWESS regression, with O+ comprising 98.3%鈥99.9% of the total loss. Escape rates at 4.0 Gyr are 2 to 3 orders of magnitude lower than during early epochs. At 0.8 Gyr, planet b exhibits 3.79脳 higher O+ escape rates than planet c, whereas by 4.0 Gyr its O+ escape rates becomes 39.5脳 lower. This reversal arises from a transition to sub-magnetosonic star鈥損lanet interactions, where the fast magnetosonic Mach number, Mf, falls below unity. Despite substantial early atmospheric erosion, both planets may have retained significant atmospheres, suggesting potential long-term habitability. These findings offer predictive insight into atmospheric retention in the Kepler-1649 system and inform future JWST observations of similar M dwarf terrestrial exoplanets aimed at refining habitability assessments.
Transformational astrophysics and exoplanet science with Habitable Worlds Observatory's High Resolution Imager
White paper submitted to the UK Space Agency's initiative "UK Space Frontiers 2035
Abstract:
Habitable Worlds Observatory (HWO) will be NASA鈥檚 flagship space telescope of the 2040s, designed to search for life on other planets and to transform broad areas of astrophysics. NASA are
seeking international partners, and the UK is well-placed to lead the design and construction of its
imaging camera 鈥 which is likely to produce the mission鈥檚 most visible public impact. Early participation in the mission would return investment to UK industry, and bring generational leadership for
the UK in space science, space technology, and astrophysics.
seeking international partners, and the UK is well-placed to lead the design and construction of its
imaging camera 鈥 which is likely to produce the mission鈥檚 most visible public impact. Early participation in the mission would return investment to UK industry, and bring generational leadership for
the UK in space science, space technology, and astrophysics.
Magma Ocean Evolution at Arbitrary Redox State
Journal of Geophysical Research: Planets American Geophysical Union 129:12 (2024) e2024JE008576
Abstract:
Interactions between magma oceans and overlying atmospheres on young rocky planets leads to an evolving feedback of outgassing, greenhouse forcing, and mantle melt fraction. Previous studies have predominantly focused on the solidification of oxidized Earth鈥恠imilar planets, but the diversity in mean density and irradiation observed in the low鈥恗ass exoplanet census motivate exploration of strongly varying geochemical scenarios. We aim to explore how variable redox properties alter the duration of magma ocean solidification, the equilibrium thermodynamic state, melt fraction of the mantle, and atmospheric composition. We develop a 1D coupled interior鈥恆tmosphere model that can simulate the time鈥恊volution of lava planets. This is applied across a grid of fixed redox states, orbital separations, hydrogen endowments, and C/H ratios around a Sun鈥恖ike star. The composition of these atmospheres is highly variable before and during solidification. The evolutionary path of an Earth鈥恖ike planet at 1 AU ranges between permanent magma ocean states and solidification within 1 Myr. Recently solidified planets typically host H 2 O ${\mathrm{H}}_{2}\mathrm{O}$ 鈥 or H 2 ${\mathrm{H}}_{2}$ 鈥恉ominated atmospheres in the absence of escape. Orbital separation is the primary factor determining magma ocean evolution, followed by the total hydrogen endowment, mantle oxygen fugacity, and finally the planet's C/H ratio. Collisional absorption by H 2 ${\mathrm{H}}_{2}$ induces a greenhouse effect which can prevent or stall magma ocean solidification. Through this effect, as well as the outgassing of other volatiles, geochemical properties exert significant control over the fate of magma oceans on rocky planets.Volatile-rich Sub-Neptunes as Hydrothermal Worlds: The Case of K2-18 b
The Astrophysical Journal Letters American Astronomical Society 977:2 (2024) l51