Something Under Mars South Pole Is 400 Degrees Hotter Than It Should Be

Two hundred to four hundred degrees Celsius. That is how much hotter the inside of Mars southern hemisphere runs than the north, according to work published in Nature on 27 August. Part of that southern interior may still be molten today.

The Mars thermal anomaly under the south pole was not found with a new instrument. Alexander Berne, a Caltech PhD now at the University of Arizona, built a model that infers interior structure from very small variations in gravity. He then fed it decades of measurements from three missions already sitting in the archive: Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter.

Why the temperature gap matters

Mars has a north south split that has bothered planetary scientists for decades. Crustal thickness differs sharply between the hemispheres. The southern highlands carry magnetic anomalies locked into iron minerals, a fossil record of a field that no longer exists. Seismic readings never matched a neatly uniform interior either.

Those read like three separate problems. A hot, partly molten southern mantle gives one cause for all three, and results that collapse several puzzles into one tend to survive scrutiny better than results that explain a single oddity.

It also feeds directly into the water question. A magnetic field strong enough and lopsided enough to leave that imprint in southern rock implies a more active early interior, and a magnetic field is what stops an atmosphere being stripped away. How long Mars held liquid water depends on how long that shielding lasted. The same logic runs through what we learn from meteorite chemistry: the early conditions decide almost everything that comes after.

What to watch next

Berne method is the part with legs. Gravity data is cheap in the sense that any orbiter with radio tracking produces it as a by-product, and every body we have orbited has an archive nobody has re-read with a modern model. Venus and the Moon are the obvious next targets.

The wider point is about instruments we already have. New telescopes such as the Roman Space Telescope get the attention and the launch coverage, but a lot of the near-term science is going to come from old data and better models. Physics results have gone the same way, as the quark gluon plasma work in small nuclei showed.

If the news has you wanting to look up, a pair of Celestron Cometron 7x50 binoculars is the standard cheap entry point for backyard observing. Mars itself needs a telescope before it shows any surface detail, so set expectations accordingly.

A planet we have circled for twenty five years turns out to be two planets stitched together, and the evidence was already on disk.

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