Mars’s Southern Mantle Is 200–400°C Hotter Than the North

Mars is divided at the surface between heavily cratered southern highlands and lower, younger northern plains. A new Nature study suggests that this contrast is not only a feature of the crust and topography: the mantle beneath the south is estimated to be 200–400°C hotter than the mantle beneath the north, and the hotter material appears softer and at least partly molten. 3

That result offers a new way to think about Mars’s “crustal dichotomy.” It points to a long-lived thermal difference inside the planet, while leaving open the question of how that difference formed.

What the study found inside Mars

The southern highlands appear to sit above a hotter, lower-viscosity mantle than the northern lowlands. In physical terms, hotter mantle rock deforms more readily; the study’s interpretation also allows for partial melting beneath the southern hemisphere. 310

The finding is significant because the surface divide is already one of Mars’s largest geological features. The southern highlands are higher and more heavily cratered, while the northern plains are lower and have been proposed as the location of an ancient ocean. Geological models also generally associate the south with thicker crust than the north. 31

The new measurements therefore suggest that Mars’s two-faced appearance may reflect an interior asymmetry as well as a difference in crustal elevation, age and thickness.

How tidal tomography revealed the thermal divide

The researchers reprocessed 16 years of precision radio-tracking data from three NASA orbiters: Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter. Tracking how Mars’s gravity affects spacecraft produces a detailed gravity field; the combined dataset is also sensitive to Martian tides, crustal thickness and other changes in the planet–spacecraft system. 2

The key signal comes from the small deformation raised in Mars by the Sun’s gravity. As Mars moves through its orbit, that tidal response changes. Instead of treating the planet as having one average tidal behavior, the researchers used tidal tomography to examine how the response varies from region to region. 812

A mantle’s temperature and physical state affect its rigidity, viscosity and ability to dissipate tidal energy. By modeling the geographic pattern of Mars’s time-varying gravitational response, the team inferred a warmer and mechanically weaker mantle beneath the south than beneath the north. The resulting estimate is a present-day thermal anomaly of roughly 200–400°C. 3

This is an indirect measurement: the spacecraft did not measure mantle temperature with a thermometer. They measured gravity and tidal behavior, then used physical models to infer the underlying structure.

Why the anomaly matters for Mars’s history

Southern magnetic anomalies

Strong remanent magnetic anomalies are concentrated mainly in Mars’s ancient southern highlands. These signals record magnetization acquired by crustal rocks when Mars had a global magnetic field. 3037

A hotter southern interior could have influenced early melting, volcanism and the formation or alteration of crust that later preserved magnetic signatures. That is a possible connection, not proof that the newly inferred anomaly alone produced the magnetic field or all of the observed crustal magnetism.

Heat, water and hydrothermal activity

Internal heat can drive volcanism and hydrothermal circulation. Previous work has associated parts of the southern highlands’ crustal magnetism with valley networks and possible hydrothermal discharge over crustal intrusions. 26

The new thermal result gives researchers another interior condition to test against Mars’s ancient hydrology. If heat persisted in the south, it could have helped sustain localized groundwater circulation or subsurface water-bearing environments. Those possibilities are relevant to the planet’s past habitability, but the finding does not demonstrate that a particular basin contained life or remained wet for a specific duration.

Tectonics and mantle motion

The anomaly also provides a constraint on competing models of early Martian evolution. Researchers have debated whether Mars experienced localized mantle convection, lithospheric recycling or limited plate-tectonic-like activity. Linear magnetic features have sometimes been cited in discussions of early plate tectonics, but that interpretation remains disputed; one NASA analysis concluded that the evidence did not strongly support Earth-like plate tectonics. 27

The study consequently does not establish that Mars had modern-style tectonic plates. It shows that any model of the planet’s early interior must account for a substantial north–south thermal contrast.

What caused the hot southern mantle?

The observation identifies an asymmetry, not its origin. Several explanations remain possible:

• An ancient giant impact: A very large early impact could have rearranged the crust and mantle, creating the surface dichotomy and leaving a thermal legacy.
• Long-lived southern convection: A persistent upwelling or plume could have transported heat toward the southern hemisphere.
• Heat trapped beneath thick structures: Thick southern crust or lithosphere could have insulated the underlying mantle and slowed cooling.

The available evidence does not decisively select one of these mechanisms. The strongest conclusion is narrower: Mars’s surface dichotomy has a deep thermal counterpart, and the southern mantle is currently inferred to be substantially hotter and weaker than the northern mantle. Further gravity, seismic and geological modeling will be needed to determine whether that contrast is a remnant of Mars’s earliest formation or part of a longer-lived pattern of interior activity.