Exoplanets & Exomoons

Super-Earths and Earth-like Exoplanets

By Keith Cowing
Status Report
May 9, 2024
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Super-Earths and Earth-like Exoplanets
(Left) Measured exoplanet radii as a function of mass relative to idealized composition curves. (Right) Radii versus density deviation relative to Earth-like. Colored symbols represent the best-characterized exoplanets with mass uncertainties below 50% and radius uncertainties below 30%. Data points from Otegi et al. (2020), Lacedelli et al. (2022), Luque & Pallé (2022), DiamondLowe et al. (2022), and Piaulet et al. (2023). Mass-radius relations from Zeng et al. (2019) and Dorn & Lichtenberg (2021). Diamond symbols with attached names indicate planets with high transmission (TSM) or emission (ESM) metrics, which makes these planets favourable targets for observational characterization: TSM > 90 if Rp ≥ 1.5 REarth, otherwise TSM > 10, or ESM > 7.5 (Kempton et al. 2018). The translation of dayside irradiation to equilibrium temperature assumes efficient global heat redistribution and a constant bond albedo of 0.5. Color deviations and trend interpretation are discussed in the main text. — astro-ph.EP

In the last few years astronomical surveys have expanded the reach of planetary science into the realm of small and dense extrasolar worlds. These share a number of characteristics with the terrestrial and icy planetary objects of the Solar System, but keep stretching previous understanding of the known limits of planetary thermodynamics, material properties, and climate regimes.

Improved compositional and thermal constraints on exoplanets below ∼2 Earth radii suggest efficient accretion of atmosphere-forming volatile elements in a fraction of planetary systems, pointing to rapid formation, planet-scale melting, and chemical equilibration between the core, mantle, and atmosphere of rocky and volatile-rich exoplanets.

Meaningful interpretation of novel observational data from these worlds necessitates cross-disciplinary expansion of known material properties under extreme thermodynamic, non-solar conditions, and accounting for dynamic feedbacks between interior and atmospheric processes.

Exploration of the atmosphere and surface composition of individual, short-period super-Earths in the next few years will enable key inferences on magma ocean dynamics, the redox state of rocky planetary mantles, and mixing between volatile and refractory phases in planetary regimes that are absent from the present-day Solar System, and reminiscent of the conditions of the prebiotic Earth.

The atmospheric characterization of climate diversity and the statistical search for biosignatures on terrestrial exoplanets on temperate orbits will require space-based direct imaging surveys, capable of resolving emission features of major and trace gases in both shortwave and mid-infrared wavelengths.

Tim Lichtenberg, Yamila Miguel

Comments: 39 pages, 11 figures; review chapter accepted for publication in Treatise on Geochemistry, 3rd edition
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Geophysics (physics.geo-ph)
Cite as: arXiv:2405.04057 [astro-ph.EP] (or arXiv:2405.04057v1 [astro-ph.EP] for this version)
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Submission history
From: Tim Lichtenberg
[v1] Tue, 7 May 2024 06:59:48 UTC (5,567 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻