Gravity-rate signature of mantle flow on Mars

Recent Mars orbiters and landers have yielded valuable insights into the planet’s surface and interior. Radio tracking of Mars Global Surveyor, Mars Reconnaissance Orbiter, and Mars Odyssey has provided detailed knowledge on Mars’ gravity field, revealing subsurface structure in the crust and mantle. Seismic observations from the InSight mission indicate that marsquakes occur more frequently than previously expected, implying ongoing interior activity. InSight data also constrain the viscosity and density structure of the interior. New interpretations of the static gravity field and seismic observations suggest large negative mass anomalies in the mantle that may be associated with a mantle plume beneath the Tharsis Rise or Elysium Region.

In this study, we investigate whether mantle flow related to such a plume produces a detectable gravity-rate signal. Using currently available viscosity and density models of Mars’ interior, we perform a parameter search over plume depth, radius, thickness, and viscosity and density contrasts relative to the surrounding mantle. For each configuration, we compute the induced long-term gravity field variations and compare them with observed static and time-varying gravity models and surface topography. We use a fast axi-symmetric Stokes mantle flow code, coupled with a Spherical Harmonics code (GSH package) that can model 3D density distributions.

Plumes with low viscosity (10²¹ Pa s), deeper presence (1300 km), and high-density contrast with the surrounding mantle (-150 kg/m³) provide the highest gravity anomaly rate (of around 20 nGal/year). Furthermore, we see that smaller mass anomalies can in certain circumstances produce stronger gravity-rate signals than large anomalies. This is contrary to the static geoid signals. Our results assess the detectability of active mantle flow with present-day data and place constraints on the physical properties of possible Martian mantle plumes. These findings provide new insight into the thermal and geodynamic evolution of Mars and other terrestrial planets.