Evolution of Mars's Atmosphere

The Early Mars Climate Problem
The morphology and the mineralogy of ancient Mars convincingly show that liquid water existed on its surface at some point in the distant past. In order to keep the liquid water from freezing, the temperature of Mars's surface must have been sufficiently warm. This indicates that ancient Mars may have had habitable, Earth-like conditions. Because Mars is relatively far from the sun, its ancient atmosphere must have provided a substantial greenhouse effect to create the required climate. However, Mars's current atmosphere is very thin, and provides almost no surface warming. So, how did Mars's ancient atmosphere support liquid water on the surface? This is known as the Early Mars Climate Problem.

At the Jet Propulsion Laboratory, Dr. Renyu Hu and I have investigated this problem by building a numerical model to trace the evolution of atmospheric species (e.g. CO2, N2, H2O, Ar) in Mars's atmosphere over the last 4 billion years. By tracking the sources and sinks of these species over time, we can reconstruct their abundances in Mars's ancient atmosphere and assess their contribution to the early Mars greenhouse effect.

A Nitrogen-Rich Atmosphere on Ancient Mars
In our first investigation, we focused specifically on the evolution of N2. Our model indicates that the ancient Martian atmosphere likely contained between 60-740 mbar N2 at 3.8 billion years ago. This result is in contrast to previous studies, which indicate that far less N2 was present. A large atmospheric N2 reservoir on ancient Mars may contribute substantially to the greenhouse effect by pressure broadening absorption lines of CO2.
  • This work is published in Nature Geoscience and on arXiv.
  • Here is the open-source code for this work.
  • Here is a recorded conference talk where I presented this work.
  • Citation: Hu, R., Thomas, T.B., A nitrogen-rich atmosphere on ancient Mars consistent with isotopic evolution models. Nat. Geosci. 15, 106–111 (2022).
Multi-species Model
In our second investigation, we are focused on simultaneously modeling the evolution of multiple important species in Mars's atmosphere. We hope that by coupling the evolution of these species, new constraints will emerge on the ancient conditions of Mars. This work is in preparation.

Modeling the Geologic Carbon Cycle

The geologic carbon cycle is a surface-mantle feedback loop that is proposed to control the atmospheric CO2 of Earth (and thus, the surface temperature) on timescales of roughly 1 million years. This mechanism is crucially important for investigating the evolution of Earth's climate and understanding Earth's ancient conditions. Moreover, if Earth is a good representative of other terrestrial exoplanets, then the geologic carbon cycle is likely important for determining their climates, and thus their habitability.

At the University of Washington, Professor David Catling and I are focused on numerically modeling the geologic carbon cycle on ancient Earth and on Earth-like exoplanets. Specifically, we are focused on investigating how the geologic carbon cycle operates during extreme glaciation states. This extreme climate state may have occured in Earth's history (Snowball Earth) and may occur in exoplanets at the outer edge of the habitable zone.

Trent Thomas


NSF Graduate Research Fellow
Department of Earth and Space Sciences
Astrobiology Program
University of Washington, Seattle


Design courtesy of Vasilios Mavroudis: Plain Academic