Investigating mantle flow on Mars

The largest volcano in our solar system, Olympus Mons, is part of the Tharsis rise volcanic complex. Studies have shown that the free-air gravity anomaly at the Tharsis rise that goes up to 3,540 mGal at Olympus Mons, cannot only be explained by a flexure in the lithosphere and requires a substantial mass anomaly in the mantle to account for the heat needed to sustain Tharsis (Root et al., 2026; Redmond and King, 2004). Corroborating this, Le Maistre et al. (2023) detected a long-term acceleration in Mars' rotation rate from InSight's RISE experiment, suggesting ongoing redistribution of mass in the Martian interior that cannot be attributed to atmospheric processes alone, pointing to active internal dynamics.

Previous work has demonstrated that time-variable gravity measurements from satellite tracking offer a promising path toward detecting active mantle flow on Mars. Low viscosity and deep plumes with high density contrast with the surrounding mantle produce the strongest gravity-rate signals, reaching up to ~20 nGal/year, values that are at the edge of current observational capabilities. However, the wide uncertainty range in plume and mantle properties, including size, temperature excess, depth, and viscosity structure, translates into a broad spread of predicted signals, preventing definitive interpretation.

To move beyond this limitation, we investigate the long-term geodynamical evolution of the Tharsis mantle plume from its initiation to the present day. We model it as the product of a multi-billion-year thermal and dynamic history, to track how the plume head and tail develop, stall, and potentially persist as a thermal anomaly in the Martian mantle. The signal detectable by satellites tracking today does not necessarily reflect an actively rising mantle plume. Instead, it could be an imprint of a residue structure, whose characteristics are shaped by Mars' long thermal history.

A central focus of our study is the role of mantle viscosity, which governs the timescales of thermal diffusion, the longevity of plume structures, and the amplitude of time-variable gravity signals. We systematically explore a range of depth-dependent viscosity scenarios based on the literature, to assess how sensitively the present-day plume state depends on these assumptions, and to identify which configurations remain consistent with existing observational constraints from InSight and orbital gravity data.

By forward-modeling the gravity-rate signatures of different plume evolution scenarios, we narrow the plausible parameter space of present-day plume states and evaluate their detectability with current and future satellite missions. Our results provide refined constraints on the physical characteristics of a possible Martian mantle plume or its remnant and offer an explanation of the gravity anomaly of the Tharsis rise. This work advances our understanding of the present-day thermal and geodynamic state of Mars, with broader implications for the long-term interior evolution of terrestrial planets.

Bibliography:

Alkahal, R., Root, B. C., Dirkx, D., Thieulot, C., Fayolle, S., Goossens, S. (under review) Investigating gravity trends from realistic simulated satellite orbits. Icarus.

Le Maistre, S., et al. (2023). Spin state and deep interior structure of Mars from InSight radio tracking. Nature, 619, 733–737. https://doi.org/10.1038/s41586-023-06150-0

Redmond, H. L., and King, S. D. (2004). A numerical study of a mantle plume beneath the Tharsis Rise: Reconciling dynamic uplift and lithospheric support models. Journal of Geophysical Research: Planets, 109, E09008. https://doi.org/10.1029/2003JE002228

Root, B. C., Qin, W., van der Tang, Y., Thieulot, C. (2026). Describing the global gravity field of Mars with lithospheric flexure and deep mantle flow. Journal of Geophysical Research: Planets, 131, https://doi.org/10.1029/2024JE008765