The weight of the lava from a massive volcanic eruption 3.5 billion years ago tilted Mars’ surface by 20 to 25 degrees, according to a study published on March 2 in the journal Nature. This lasted for 200 million years, creating the Tharsis dome, a plateau more than 5,000 square kilometres wide and 12 kilometres thick.

“If a similar shift happened on Earth, Paris would be in the Polar Circle,” says Sylvain Bouley, a geomorphologist at Université Paris-Sud. “We’d see Northern Lights in France, and wine grapes would be grown in Sudan.”

Bouley’s team matched their own simulations with findings of other scientists. The scientist adds that the Tharsis dome is large, which he describes as an aberration in relation to the size of the Red Planet.

Apparently, it weighed billions of tonnes and caused the planet’s crust and mantel to spin around. A study presented in 2010 said that Tharsis is so huge that if the dome is removed, the planet would shift on its axis.

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Mars: Exposure of silica-rich dust uncovered by the Spirit rover. Photo by NASA

The scientists say that this also explains the unexpected location of dry river beds and underground reservoirs of water ice. They said that the big underground reservoirs of frozen water ice should have been closer the planet’s poles instead of the random areas they are in today.

“Scientists couldn’t figure out why the rivers — dry river beds today — were where they are. The positioning seemed arbitrary. But if you take into account the shift in the surface, they all line up on the same tropical band,” Bouley adds. “Likewise, the huge underground reservoirs of frozen water ice that should be closer to the poles. Once upon a time, we now know, they were.”

The team speculates that these waterways would have flowed from Mars’ cratered highlands in the southern hemisphere to the low plains of the northern hemisphere. They also think that their study demonstrates that rivers were not formed after the creation of the Tharsis dome.

However, Bouley points out that a lot is still unknown. “Did the tilt cause the magnetic fields to shut down? Did it contribute to the disappearance of Mars’ atmosphere, or cause the rivers to stop flowing? These are things we don’t know yet.”