A Massive Primordial Atmosphere On Early Mars

Mars finished forming while the solar nebula was still present, and acquired its primordial atmosphere from this reservoir.

The absence of a detectable cometary xenon signature in the present-day Martian atmosphere suggests that the capture of solar nebular gas was significant enough to dilute later cometary contributions. By quantifying the mass of cometary material efficiently retained on Mars, we place a lower bound on the mass of the primordial Martian atmosphere.

To test the robustness of our conclusions, we use cometary bombardment data from two independent studies conducted within a solar system evolutionary model consistent with its current structure. Our calculations show that, even under the most conservative scenario, the minimal mass of the primordial martian atmospheres would yield a surface pressure of no less than 2.9 bar.

Such a massive nebular envelope is consistent with recent models in which atmospheric capture is strongly enhanced by the presence of heavier species on Mars – due to outgassing or redox buffering with a magma ocean.

Sarah Joiret, Alessandro Morbidelli, Rafael de Sousa Ribeiro, Guillaume Avice, Paolo Sossi

Comments: Accepted at EPSL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2509.10060 [astro-ph.EP] (or arXiv:2509.10060v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.10060
Focus to learn more
Submission history
From: Sarah Joiret
[v1] Fri, 12 Sep 2025 08:47:32 UTC (140 KB)
https://arxiv.org/abs/2509.10060
Astrobiology,