Mars’s interior is likely 200 to 400 degrees Celsius hotter beneath its southern hemisphere than in the north, according to a study published in Nature. Researchers used “tidal tomography” to analyze 16 years of spacecraft data, revealing a deep thermal asymmetry that suggests the southern mantle is softer and potentially more iron-rich than the northern region.
Tidal Tomography Reveals Martian Mantle Asymmetry
Scientists analyzed radio-tracking data from three NASA orbiters: the Mars Global Surveyor, Mars Odyssey, and the Mars Reconnaissance Orbiter. By observing how the planet’s gravity field and shape responded to the seasonal redistribution of carbon dioxide ice—which freezes at one pole and evaporates at the other—the team could probe the interior without using seismic waves.
This method revealed that the mantle shear modulus, which measures resistance to deformation, varies by more than 20% across the planet. The strongest anomaly is located beneath the southern highlands. Dr. Alexander Berne, who is a postdoctoral associate at the University of Arizona who conducted the research as a PhD student at Caltech, and is lead author of the study, stated that while scientists usually assume planetary interiors are spherically symmetric, this is not necessarily true.
Did you know? Mars has a much more oval-shaped orbit than Earth. Its eccentricity is 0.093, compared to Earth’s 0.017, and its planetary tilt is 25.19 degrees, slightly steeper than Earth’s 23.44 degrees.
Temperature Inferences vs. Direct Measurement
The reported temperature difference of 200-400°C (392-752°F) is an inference based on mantle rigidity rather than a direct thermometer reading. The research team tested models varying both heat and iron composition to explain the data; their preferred models suggest the southern mantle is warmer and may contain up to 5% more iron.
This thermal contrast does not prove the existence of a continuous molten layer or a global magma ocean. Warmer rock can remain solid while flowing extremely slowly over geological timescales, though localized partial melting remains a possibility. These findings build on past findings from the now-retired NASA InSight lander that discovered seismic waves that passed through the southern hemisphere’s interior dissipated quicker than seismic waves passing through the northern hemisphere’s interior.
Geological Divide Between Northern Lowlands and Southern Highlands
The interior heat disparity mirrors the stark contrast seen on the Martian surface. The northern hemisphere consists of vast plains known as the northern lowlands, while the southern hemisphere is dominated by the southern highlands and vast mountain ranges. The only major exception is the Hellas basin, a massive impact site in the south that sits thousands of meters lower than the northern average elevation.
Researchers suggest the thicker crust of the southern hemisphere may have insulated its interior heat, preventing it from cooling as rapidly as the rest of the planet billions of years ago. This asymmetry could be the result of ancient giant impacts, extra radioactive heating, or long-lived mantle upwelling.
Expert Insight: Understanding the interior structure of planetary bodies helps us unravel the processes that shaped their formation and evolution, and gives us a blueprint for designing future missions and scientific exploration of these worlds.
Comparison of Research Framing
Different scientific outlets have highlighted different implications of the Nature study:
| Source | Primary Focus |
|---|---|
| Nature | The tidal tomography methodology. |
| Caltech | The thermal anomaly under the south polar region. |
| Science Times | Speculation regarding partial melting. |
Frequently Asked Questions
Does this mean there is magma on Mars today?
Not necessarily. While the southern mantle is warmer, the measurements do not establish a continuous molten layer; warmer rock can remain solid while flowing very slowly.
How does this affect the search for life?
A warm mantle is not direct evidence for current eruptions, accessible liquid water or life. According to the researchers, these possibilities require separate observations.
What spacecraft provided the data?
The study used archival and active data from NASA’s Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter.
Join the conversation: Do you think the thermal asymmetry of Mars suggests the planet is more geologically active than we previously thought? Let us know in the comments below or subscribe to our newsletter for more space exploration updates.