Mars tidal data uncovers a deep thermal hotspot beneath the southern highlands
Analysis of 16 years of spacecraft tracking shows unexpected degree-3 gravity variations on Mars, pointing to a north-south mantle stiffness contrast and a 200-400 °C thermal anomaly under the southern highlands.
A team examined sixteen years of X-band Doppler tracking from the Mars Global Surveyor, Odyssey and Reconnaissance Orbiter to retrieve Mars's time-variable gravity field at the annual (687-day) period. They discovered that the degree-3 spherical-harmonic coefficients deviate by as much as 300 % from values expected for a spherically symmetric planet, a signal that can only be produced by lateral heterogeneity in the mantle's shear modulus.
Bayesian inversions of the gravity data reveal north-south, east-west and meridional shear-modulus variations exceeding 20 % and matching the surface expression of the crustal dichotomy. Converting the stiffness contrast to temperature using anelastic rheology suggests a persistent thermal anomaly of 200-400 °C beneath the southern highlands, consistent with either mantle upwelling or thermal insulation by the thick southern crust.
The study links deep-mantle structure to the long-standing debate over the dichotomy’s origin and offers a new tool—tidal tomography—for probing planetary interiors. Future missions with dedicated gravity experiments could refine these observations and extend the method to other bodies.
Why it matters
It reveals hidden heat beneath Mars’s southern highlands, reshaping theories of the planet’s formation and interior dynamics.
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