[LINK] "An Ancient Volcanic Cataclysm Spun Mars Off Its Poles"

[rfmcdonald]

Universe Today's Evan Gough looks at new research suggesting a catastrophic history for Mars.

According to a new research paper from Sylvain Bouley at the University of Paris-South, and his colleagues, it may have been a massive, ancient outpouring of molten rock that threw Mars off kilter and helped change Mars into what it is today.

The Tharsis region is an ancient lava complex on Mars that dates back to between 4.1 billion and 3.7 billion years ago. It’s located in Mars’ Western Hemisphere, right near the equator. It’s made up of three huge shield volcanoes—Arsia Mons, Pavonis Mons, and Ascraeus Mons. Collectively, they’re known as Tharsis Montes. (Olympus Mons, the largest volcano in the Solar System, is not a part of the Tharsis complex, though it is near it.)

Tharsis is over 5,000 km across and over 10 miles thick, making it the largest volcanic complex in the Solar System. That much mass positioned after Mars was already formed and had an established rotation would have been cataclysmic. Think what would happen to Earth if Australia rose up 10 miles.

The new paper, published on March 2nd, 2016, in the journal Nature, says that the position of the Tharsis complex would have initiated a True Polar Wander (TPW.) Basically, what this means is that Tharsis’ huge mass would have forced Mars to shift its rotation, so that the location of Tharsis became the new equator.

It was thought that the emergence of Tharsis made Martian rivers—which formed later—flow the direction they do. But the study from Bouley and his colleagues shows that Martian rivers and valleys formed first—or maybe concurrently—and that the Tharsis TPW deformed the planet later.

The authors of the study calculated where the Martian poles would have been prior to Tharsis, and looked for evidence of polar conditions at those locations. The location of this ancient north pole contains a lot of ice today, and the location of the ancient south polar region also shows evidence of water.

The Nature paper is here.

The Tharsis region is the largest volcanic complex on Mars and in the Solar System. Young lava flows cover its surface (from the Amazonian period, less than 3 billion years ago) but its growth started during the Noachian era (more than 3.7 billion years ago). Its position has induced a reorientation of the planet with respect to its spin axis (true polar wander, TPW), which is responsible for the present equatorial position of the volcanic province. It has been suggested that the Tharsis load on the lithosphere influenced the orientation of the Noachian/Early Hesperian (more than 3.5 billion years ago) valley networks and therefore that most of the topography of Tharsis was completed before fluvial incision. Here we calculate the rotational figure of Mars (that is, its equilibrium shape) and its surface topography before Tharsis formed, when the spin axis of the planet was controlled by the difference in elevation between the northern and southern hemispheres (hemispheric dichotomy). We show that the observed directions of valley networks are also consistent with topographic gradients in this configuration and thus do not require the presence of the Tharsis load. Furthermore, the distribution of the valleys along a small circle tilted with respect to the equator is found to correspond to a southern-hemisphere latitudinal band in the pre-TPW geographical frame. Preferential accumulation of ice or water in a south tropical band is predicted by climate model simulations of early Mars applied to the pre-TPW topography. A late growth of Tharsis, contemporaneous with valley incision, has several implications for the early geological history of Mars, including the existence of glacial environments near the locations of the pre-TPW poles of rotation, and a possible link between volcanic outgassing from Tharsis and the stability of liquid water at the surface of Mars.