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.