When Mars Tipped Over

How a bulge of volcanoes shaped the Red Planet.

By Eric Betz|Thursday, October 06, 2016
RELATED TAGS: SOLAR SYSTEM, MARS
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Four massive volcanoes make up the Tharsis Bulge on Mars. The largest of the four, Olympus Mons, is at bottom right.
ESA/DLR/FU Berlin/Justin Cowart

For hundreds of millions of years, lava bubbled up from the depths of Mars, forming a staggering volcano system called the Tharsis Bulge. Its four major volcanoes near the equator — including Olympus Mons, the solar system’s largest — are all taller than Mount Everest. And now, new research reveals that the bulge’s massive size had serious consequences for the Red Planet.

According to a French-led team, the bulge made Mars tip over some 3 billion years ago. Its outer layers, the crust and mantle, rotated until the enormous volcanoes traveled about 20 degrees, from the polar regions down toward the equator.

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New research indicates that the load of Mars’ Tharsis bulge caused the planet’s outer layers to rotate. As a result, the planet’s axis reoriented — a phenomenon called true polar wander (TPW) — and tipped about 20 degrees, as this image shows. (Warmer colors denote higher elevations.)
Sylvain Boulet et al./Macmillan Publishers ltd/Nature/Vol 531, March 17, 2016
The research, published in Nature, rewrites the first billion years of Martian history. The team’s climate modeling contradicts existing theory by showing that the river valleys seen on Mars could’ve flowed while Tharsis was still forming, instead of emerging afterward. And the eruption of water-rich gases would’ve helped fuel Mars’ early atmosphere for a while, driving precipitation on a wet planet. But by the time the Tharsis volcanoes let out their final breath, the heat was gone, and the planet was abandoned to an endless, dry winter — a world not too different from what we see today.
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