A picture of Mars today looks much different than what it looked like about 3 billion years ago. New research is out describing a “huge tilt” that tilted the red planet by 20 to 25 degrees. Folks a lot smarter than us figured out what caused the tilt.

Geomorphologists, geophysicists and climatologists figured out Mars’ tilt wasn’t caused by the planet’s rotation axis. Instead, the incredible mass of the Tharsis volcanic dome caused the crust and mantle of Mars to rotate around its core.

A trip to Mars’ ancient past

3.7 billion years ago, a massive structure began forming on the surface of Mars. Today, we call it the Tharsis volcanic dome. It first formed at a latitude of around 20 degrees North. For several hundred million years, all sorts of volcanic activity created a plateau more than 5,000 kilometers in diameter and about 12 kilometers thick with a mass of billion billion tons. So yeah, it was huge.

It was so huge, it caused Mars’ crust and mantle to shift. The Tharsis volcanic dome started at 20 degrees North. Today? It sits at the red planet’s equator.

old face of Mars

The old face of Mars

The ramifications of the Tharsis volcanic dome are huge. 3.7 billion years ago, Mars’ poles would have been in different positions. Research by Isamu Matsuyama (from the University of Arizona) backs this up. In 2010, Matsuyama used a geophysical model to show what would happen if you took the Tharsis dome away from Mars. Because it’s so massive, removing it would change the planet’s orientation.

Fast forward to today and research from geomorphologists Sylvain Bouley and David Baratoux show where rivers were originally distributed.

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According to scientists, “the rivers were originally distributed along a south tropical band on a planet Mars that rotated around poles shifted by about 20 degrees with respect to their current positions. These poles are consistent with those calculated independently by Matsuyama.”

Other observations backup Mars’ ancient poles including hints of glacier melting and evidence of ice below the surface where the polar regions used to be.

This new research answers three mysteries of Mars. It tells scientists why rivers formed where we see them today, why evidence of subsurface ice is seen far from today’s polar regions and why the Tharsis dome sits near the equator.

Besides changing the way we think of ancient Mars, the new research also changes the timeline of events and how we should look at Mars today. The scientists believe the period of liquid water stability that helped make the formation of river valleys possible was a result of the volcanic activity at the Tharsis dome. Plus, scientists exploring Mars should take into account the new geography proposed by this new research according to the scientists behind the study.

Mars’ ancient puzzle is far from complete. This new research adds a few new pieces to it, but it doesn’t answer several fundamental questions. What happened to Mars’ magnetic fields? The planet’s atmosphere? All of the water? Those mysteries are for another day, but now we know the face of Mars looked much different billions of years ago.

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