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

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. 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. 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. Quick fact: Other recent insights about Mars’ interior Last year, two teams of researchers reported strange discoveries about the Red Planet’s innards using InSight data.

One suggests that Mars’ mantle preserves the remains of smaller planetary bodies that once collided to create the planet. The other hinted that Mars has a solid inner core. The underground heat difference could explain other odd Martian features.