Martian Tharsis bulge’s volcanic history

The Mars Express mission, launched in 2003, aims to study of the atmosphere, surface, subsurface and interior of Mars.  While the Beagle 2 lander, due to land of Mars on Christmas day 2003, failed to communicate and was declared lost in February 2004, the orbiter has been successfully doing science since 2004. A series of on-board instruments have been mapping the surface at high resolution (10m/pixel globally and 2m/pixel in targeted areas), producing surface mineral composition maps, probing the subsurface structure to depths of a few kilometres, determining the composition and circulation of the atmosphere,  as well as studying the effect of the atmosphere on the surface and the interaction of the solar wind with the atmosphere.

With more than five years of high resolution gravity data produced by radio tracking of  Mars Express and the Mars Reconnaissance Orbiter, Mikael Beuthe from the Royal Observatory of Belgium and collaborators have gained unique insights into the structure and formation of the Mars’ largest volcanoes.  The enormous mass of the volcanic Tharsis bulge region on Mars, which hosts the Solar System’s largest  volcano Olympus Mons which reaches a height of 21 km, perturbs the trajectory of Mars Express as it flies overhead. These wobbles produce a Doppler shift in the spacecraft’s radio signal which is measured from Earth and translated into measurements of density variations below the surface.

The three Tharsis Montes and Olympus Mons as seen from the Mars Global Surveyor. (Credits: NASA)

The new data suggests that the three Tharsis Montes – Arsia, Pavonis and Ascraeus Mons – formed one by one, starting in the south with Arsia Mons, possibly by a single mantle plume moving under the surface. The gravity data indicates that the lava became denser over time and the thickness of the crust varies across the region, suggesting that the lava density changed during the build up of the three Tharsis Montes volcanoes.  These density changes could reflect changes in heating processes beneath the surface in the form of a single mantle plume, an upwelling of abnormally hot rock from deeper within the viscous mantle which slowly moved sideways to create each of the three Tharsis Montes in turn.  For more information, see

[Francesco Pignatale, Guido Moyano Loyola & Sarah Maddison]

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