CosmicGravity · News & analysis · September 5, 2026

Mars looks cold, dusty and still. Its interior is a different story. A new study suggests that parts of the mantle beneath the southern hemisphere are substantially hotter than their northern counterparts.

The new Mars southern mantle heat research, described by Caltech on August 26, uses spacecraft tracking to investigate how the planet responds to the Sun’s gravitational pull. The researchers’ models indicate a southern region roughly 200–400 degrees Celsius warmer than the comparison northern mantle, with partial melting possible. These are inferred differences deep inside Mars, not temperatures measured at the surface. Caltech’s report sets out the approach.

Using an orbit as a probe

The study draws on tracking of Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter. Small changes in their motion carry information about gravity. Because the Sun’s pull slightly deforms Mars, the way that gravitational field varies can reveal properties of the interior.

This is an indirect measurement. The analysis connects observed orbital behaviour to physical models; it does not photograph a chamber of magma. The Nature study on tidal tomography investigates the relationship between that response and the planet’s striking north–south crustal contrast.

Why one half of a planet might keep more heat

Mars’s southern highlands and northern lowlands have long posed a geological puzzle. The new work explores possible contributors to the thermal contrast, including differences in crustal insulation, the redistribution of heat in the mantle and the consequences of ancient impacts. The measurement does not select a single, finished origin story.

That distinction makes the finding more useful, not less. Each explanation implies a somewhat different history. Future measurements can test which combination fits the rest of what we know about Mars.

How this fits with InSight

NASA’s InSight lander investigated the interior through seismic waves. Its results helped reveal the structure of the crust, mantle and core. NASA’s InSight explainer shows how waves passing through different materials provide clues that surface photographs cannot.

Spacecraft tracking and seismology ask related questions with different tools. Agreement between them can strengthen an interpretation; disagreement can expose an assumption that needs work.

None of this establishes a hidden ocean or underground organisms. Heat is relevant to a planet’s evolution and potentially to habitability, but it is only one ingredient. Water, chemistry, energy sources and their persistence would all need separate evidence.

That is the thread connecting Mars to our coverage of Europa’s ocean and Enceladus’s plumes: discovering a promising environment is the beginning of the search, not its conclusion.

Lead image: Historical Mars Global Surveyor mosaic of Tharsis and Valles Marineris, April 1999. This is a surface view, not a thermal image of the new anomaly. NASA/JPL/MSSS. Image source and usage information.

Editorial note: Reporting checked September 5, 2026. Linked sources distinguish the underlying observations from interpretation. Future plans and preliminary results may change.