Reduced late bombardment on rocky exoplanets around M dwarfs

Press release

astro-ph.EP

September 28, 2022

Illustration of the planet formation scenario incorporated into the N-body and long-term planetesimal bombardment simulations, described in more detail in Clement et al. (2022a). Varying initial conditions related to the water content of embryos and planetesimals in the three regions simulate different physical scenarios of material devolatilization and redox gradients (Lichtenberg et al. 2022) across the planetesimal disk.

astro-ph.EP

Oceanic vaporization impacts of chemically reduced planetesimals on early Earth have been suggested to catalyze atmospheric production of reduced nitrogen compounds and trigger prebiotic synthesis despite an oxidized lithosphere.

While geochemical evidence supports a dry and strongly reduced late plating on Earth, the composition of late-impact debris around lower-mass stars is subject to variable volatile loss due to the prolonged pre-main sequence phase of their hosts. . We run simulations of late-stage planet formation across the M-dwarf mass spectrum to derive upper bounds on the reduction of bombardment epochs in analog Hadean environments.

We compare the solar system scenario with variable initial volatile distributions due to prolonged primordial greenhouse gas phases on protoplanets and desiccation of smaller planetesimals by internal radiogenic heating.

We find a decreasing rate of late accretion-reducing impacts with decreasing stellar mass. Young planets around stars ≤0.4 M⊙ experience no impact of sufficient mass to generate relevant prebiotic concentrations of reduced atmospheric compounds once their stars have reached the main sequence.

For M dwarf planets not to exceed Earth-like volatile compound concentrations, larger planetesimals and protoplanets must undergo extensive devolatilization processes and can usually emerge from long-lived magmatic oceanic phases with sufficient atmosphere content to degas secondary atmospheres. Our results suggest that the transient reduction of surface conditions on young rocky exoplanets is favored around FGK stellar types over M dwarfs.

Tim Lichtenberg, Matthew S. Clement

Comments: 17 pages, 3 figures, 1 table; accepted for publication in ApJL
Subjects: Terrestrial and planetary astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2209.14037 [astro-ph.EP] (or arXiv:2209.14037v1 [astro-ph.EP] for this release)
Submission history
By: Tim Lichtenberg
[v1] Tue Sep 27 2022 2:25:48 PM UTC (595 KB)
https://arxiv.org/abs/2209.14037
Astrobiology

Co-founder of SpaceRef, member of the Explorers Club, ex-NASA, external teams, journalist, space and astrobiology, deceased climber.

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