Evolving Atmospheric Ion Escape from Kepler-1649 b and c: Power-Law Trends in Atmospheric Loss
ApJL in review
Abstract:
Rocky planets orbiting M-dwarf stars are prime targets for characterizing terrestrial atmospheres, yet their long-term evolution under intense stellar winds and high-energy radiation remains poorly understood. The Kepler-1649 system, which hosts two terrestrial exoplanets orbiting an M5V star, presents a valuable opportunity to explore atmospheric evolution in the extreme environments characteristic of M-dwarf stellar systems. In this Letter we show that both planets could have retained atmospheres over gigayear timescales. Using a multi-species magnetohydrodynamic model, we simulate atmospheric ion escape driven by stellar winds and extreme ultraviolet radiation from 0.7 to 4.8 Gyrs. The results show that total ion escape rates follow a power-law decline (∝ τ ^−1.6 for Kepler-1649 b, ∝ τ ^−1.5 for Kepler-1649 c ), with O+ dominating atmospheric loss (76.8%–98.7%). The escape rates at 4.8 Gyrs are two orders of magnitude lower than those during the early epochs (1.9 × 1027 s^−1 at 0.7 Gyr vs. 3.0 × 1025 s^−1 at 4.8 Gyrs for planet b ), while planet b consistently exhibits 1.1–1.9× higher O+ escape rates than planet c due to its closer orbit (0.051 AU vs. 0.088 AU). Despite substantial early atmospheric erosion, both planets may still retain significant atmospheres, suggesting the potential for long-term habitability. These findings offer predictive insight into atmospheric retention in M-dwarf systems and inform future JWST observations aimed at refining habitability assessments.
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.
archNEMESIS: An Open-Source Python Package for Analysis of Planetary Atmospheric Spectra
Journal of Open Research Software Ubiquity Press 13:1 (2025)
Abstract:
ArchNEMESIS is an open-source Python package developed for the analysis of remote sensing spectroscopic observations of planetary atmospheres. It is based on the widely used NEMESIS radiative transfer and retrieval tool, which has been extensively used for the investigation of a wide variety of planetary environments. The main goal of archNEMESIS is to provide the capabilities of its Fortran-based predecessor, keeping or exceeding the efficiency in the calculations, and benefitting from the advantages Python tools provide in terms of usability and portability. ArchNEMESIS enables users to compute synthetic spectra for a wide variety of planetary atmospheres, supporting multiple spectral ranges, viewing geometries (e.g., nadir, limb, and solar occultation), and radiative transfer scenarios, including multiple scattering. Furthermore, it provides tools to fit observed spectra and retrieve atmospheric and surface parameters using both optimal estimation and nested sampling retrieval schemes. The code, stored in a public GitHub repository under a GPL-v3.0 license, is accompanied by detailed documentation available at https://archnemesis.readthedocs.io/.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