Mars Is Two-Faced. Deep Down, Only One Side Runs Hot.

Far below the battered southern highlands of Mars, the rock is 200 to 400 degrees Celsius (360 to 720 degrees Fahrenheit) warmer than the rock beneath the north.

Nobody drilled to find this. In an Aug. 26, 2026, paper in Nature, a Caltech team led by Alexander Berne reported reading the heat from orbit, by way of gravity. Antennas on Earth tracked tiny shifts in the speed of three orbiters (Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter) across roughly 16 years of data. Those shifts map the pull of the ground below.

The sun's tides flex Mars over each 687-day Martian year. A planet built evenly inside should answer in a tidy, predictable way. Mars does not. Some of its gravity signals stray up to 300 percent from that prediction, which the team reads as softer mantle rock under the south. Heat, they infer, explains most of the softness.

The pattern traces the planet's famous split. The north is largely low, smooth plain; the south is high, rugged and pocked with craters. That lopsidedness, it seems, is not skin deep.

Why the south stays warm is still open. The researchers offer three candidates: a giant impact, heat churning through the southern mantle or a thick southern crust acting as a blanket. The split may also hold clues to basins that could once have held water.

Somewhere beneath Hellas basin, Mars is running a temperature. Three spacecraft diagnosed it without ever laying a hand on the patient.

Read the full story at EarthSky, September 4, 2026

Hot Take: Future Mars settlers will want to ask the estate agent which side of the divide comes with underfloor heating.