About 3.5 billion years ago, the Red Planet underwent a cataclysmic event. The surface of Mars tilted by 20 to 25 degrees, caused by a massive volcanic structure, which gives Mars the new face that we see today.
Mars hasn't always looked like it does today. About 3 to 3.5 billion years ago, the planet underwent a huge tilt, which has now been identified thanks to the combined work of geomorphologists, geophysicists and climatologists. It wasn't the rotation axis of Mars that shifted, but rather the outer layers that rotated with respect to the inner core, rather like turning the flesh of an apricot around its stone. This phenomenon had been predicted theoretically, but never demonstrated.
The tilt itself was actually caused by the gigantic Tharsis volcanic dome, which first started to form more than 3.7 billion years ago at a latitude of around 20 degrees North. This dome is the largest in the solar system, and its volcanic activity continued for several hundred million years, forming a plateau exceeding 5,000 km in diameter. Eventually, the mass was so huge that it caused Mars' crust and mantle to swivel around, shifting the Tharsis dome to the equator.
Before this cataclysmic event, the poles of Mars were not in the same place that they are today. In fact, the rivers that scientists have found today were originally distributed along a south tropical band.
This shift would have had a significant impact on the planet. This means that understanding the topography before the tilt could be used to study the early climate of the planet. It's likely that Mars had a cold climate and an atmosphere that was denser than it is today. In addition, ice accumulated in regions corresponding to the sources of now dry river beds.
The new findings change our perspective of the surface of Mars as it was 4 billion years ago and also significantly alters the chronology of events. According to the new scenario, the period of liquid water stability that allowed the formation of river valleys is contemporaneous with, and most likely a result of, the volcanic activity of the Tharsis dome.
The findings tell researchers a bit more about past climate, which could allow them to target specific locations as they hunt for the possibility of past life on the Red Planet.
