- Mars is a cold world, with ice caps and lots of ice below the surface.
- But new research has discovered strange excess heat deep below the surface of southern hemisphere.
- Explanations range from a giant impact releasing thermal energy to thick geological features trapping heat.
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Mars’ southern hemisphere is unexpectedly hot deep below the surface
Mars is a very cold planet on the surface. Like Earth, it gradually gets warmer the deeper you go into its interior. But now, researchers at Caltech in California have found an unusual anomaly. They said on August 26, 2026, that there’s a huge excess of heat deep below Mars’ surface in the southern hemisphere. In fact, the region is about 200-400 degrees Celsius (290-750 degrees Fahrenheit) hotter than expected.
The heat anomaly seems to mirror the north-south asymmetry of Mars. The planet’s northern hemisphere is mostly flat lowlands, while the southern hemisphere is covered by craters and mountains. Because of this, Mars sometimes is referred to as as being “two-faced.” Now it seems that rather than being simply a surface feature, that characteristic runs deep into the inside of the planet as well.
The researchers published their peer-reviewed findings in Nature on August 26, 2026.
Measuring spacecraft velocities
How did the researchers discover this anomaly? Caltech alumnus Alexander Berne led the new study. Berne and his team used data collected over decades from three different Mars missions: Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter. The team measured tiny variations in the spacecrafts’ velocities and then used them to reconstruct the gravitational field around Mars.
Using a technique called tidal tomography, or planetary tomography, the researchers measured how those gravitational signatures vary over time. This enabled the team to create a model of the planet’s interior. As Berne explained:
Scientists usually assume that the interiors of planetary bodies are generally spherically symmetric, but this is not necessarily true. As we get more gravity data, we can determine the three-dimensional intricacies of a planet’s interior structure. These inferences in turn give us a blueprint for designing future missions and scientific exploration of these worlds. Understanding the interior structure of planetary bodies helps us unravel the processes that shaped their formation and evolution.
An unbalanced interior
Like Earth, Mars isn’t perfectly spherical. The northern lowlands are mostly quite flat, while the southern hemisphere has mountains and many deep craters. And this is where the thermal anomaly comes in. The interior of the southern hemisphere is much hotter than the north, by about 200-400 degrees Celsius (290-750 degrees Fahrenheit). At those temperatures, the rock is partially molten.
What could explain Mars’ southern hemisphere anomaly?
The researchers have proposed a few hypotheses to explain the anomaly. One is a giant impact that released heat from the northern hemisphere.
Another possibility is spontaneous convection – the movement of heat through fluids – in the southern mantle.
Finally, it could be caused by thick geological features in the southern hemisphere that trap excess heat from escaping.
The findings also have implications for the geological history of Mars and its habitability billions of years ago. Co-author Amirhossein Bagheri, a postdoctoral scholar at Caltech, said:
The dichotomy that we see between north and south is important to understand because it gives information about processes that may have influenced the hydrology of Mars, including the formation of basins that may have held water.
Bottom line: A new study from Caltech shows that Mars’ southern hemisphere is much hotter than expected deep below the surface. Why is that?
Source: Tidal tomography reveals a thermal anomaly beneath Mars’s crustal dichotomy
Via Caltech
Read more: Mars’ interior might contain remnants of baby planets
Read more: Marsquakes might explain Mars’ north-south hemisphere differences