Mars’ Southern Half Is Weirdly Warm Underground. The ‘Thermal Anomaly’ Might Explain Why the Planet’s Hemispheres Look So Different

Researchers used a novel technique to figure out what’s going on inside the Red Planet. The work suggests that the interior of the southern hemisphere is hundreds of degrees hotter than that of the northern hemisphere and partially molten

Margherita Bassi | Daily Correspondent

September 1, 2026 11:47 a.m.

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Mars is a strange-looking planet. Its northern and southern halves take on vastly different appearances. While the north is characterized by low flat lands, the south features dramatic mountains and craters. Now, researchers seem to have discovered another surprising dichotomy, but this time deep beneath the Red Planet’s surface.

The interior of Mars’ southern hemisphere is hundreds of degrees hotter than its other half, according to a study published August 26 in the journal Nature. The findings might help explain several strange Martian phenomena and could help inform a longstanding question about our neighboring planet: Did it once have the conditions to host life?

Much of our knowledge about Mars’ insides comes from NASA’s InSight Lander, which detected seismic waves on the planet from late 2018 through late 2022. But relying on just one station, which sat near the planet’s equator, meant most models of the interior assumed it is uniform all the way around, reports Scientific American’s Jacek Krywko.

The researchers behind the new work used a different approach. They took advantage of variations in the Red Planet’s gravitational field, which can reveal secrets about Mars’ internal structure. These gravitational changes happen seasonally because of Mars’ oval-shaped orbit and tilted rotational axis, which regularly affects the sun’s gravitational influence on the planet.  

“That creates a tidal force, and the tidal force changes Mars’ shape over the year,” study co-author Alexander Berne, a planetary scientist at the University of Arizona, tells Scientific American. 

Berne and colleagues examined 16 years’ worth of data from three NASA spacecraft that circled the Red Planet: the Mars Global Surveyor, the Mars Odyssey and the Mars Reconnaissance Orbiter. Minute changes in the spacecrafts’ velocities, which hinted at changes in the planet’s gravitational field, helped the team build a model of Mars’ interior. The work suggested that the southern hemisphere is roughly 400 to 750 degrees Fahrenheit hotter than the northern half and partially molten.

“I was kind of surprised how sharp the result was, and how confident it was,” study co-author Nick Wagner, a geoscientist at Brown University, tells 404 Media’s Becky Ferreira. “But maybe we shouldn’t be surprised, because Mars seems to be dominated by these large-scale variations from the north to south, so it makes sense that these variations also extend into the mantle,” the layer below the crust.

What’s more, the team’s modeling indicates that the temperature asymmetry below the planet’s surface closely follows the north-south geographical boundary above.

The underground heat difference could explain other odd Martian features. For example, scientists have detected magnetic anomalies in iron minerals in the planet’s southern hemisphere. The interior thermal asymmetry could point to a past magnetic field so strong that it caused magnetic differences between the northern and southern hemispheres. Furthermore, InSight data revealed that seismic waves dispel faster in the south, which might result from the area being hotter.

“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,” study co-author Amirhossein Bagheri, a planetary scientist at Caltech, says in a statement.

An increasing body of research indicates that Mars was once a watery world, and this bygone hydrology is of particular interest to researchers looking for signs of past Martian life. Because water is crucial for life on Earth, its presence plays a key role in scientists’ search for habitability on other worlds.

But what caused this difference in the distribution of Mars’ internal heat? That’s still up for debate, but there are several hypotheses.

One suggests that a large impact caused the northern hemisphere to release its heat. Another posits that spontaneous upwelling brings heat from the core to Mars’ southern mantle. Alternatively, the strange warmth might come from thick geological features in the south preventing extra heat from dissipating. The south’s crust is, on average, about 15.5 miles thicker than that in the northern half, after all.

Regardless, there are still uncertainties, Paul Byrne, a planetary geologist at Washington University in St. Louis who did not participate in the study, tells Scientific American. For example, he wonders why Mars’ largest volcanic province is near the equator—on the margins of the thermal anomaly—and not above the study’s identified hotter region.

Wagner also has lingering questions. “I’m wondering how this anomaly plays into the idea of Mars maybe having the ability to have plate tectonics at one point, or maybe not having the ability,” he tells 404 Media. “It’s another piece in this puzzle to figure out what past Mars looked like, both habitability-wise, but also just for pure science.”

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.