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 ± 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 ⊙ and mean molecular weight > 7.1 g mol −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 ×10−5 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.
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‐similar planets, but the diversity in mean density and irradiation observed in the low‐mass 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‐atmosphere model that can simulate the time‐evolution of lava planets. This is applied across a grid of fixed redox states, orbital separations, hydrogen endowments, and C/H ratios around a Sun‐like star. The composition of these atmospheres is highly variable before and during solidification. The evolutionary path of an Earth‐like planet at 1 AU ranges between permanent magma ocean states and solidification within 1 Myr. Recently solidified planets typically host H 2 O ${\mathrm{H}}_{2}\mathrm{O}$ ‐ or H 2 ${\mathrm{H}}_{2}$ ‐dominated 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
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