Image 1 - Mars Express Helps Map History Of Martian Volcanic History
April 27, 2012

Mars Express Helps Map History Of Martian Volcanic History

Lee Rannals for

Mars Express has helped to unveil volcanic history of the Red Planet, providing more insight as to what lies underneath our celestial neighbor.

The spacecraft has been floating above Mars, mapping out the planet, for five years, during which it has helped researchers find that lava grew denser over time, and that the thickness of the planet's rigid outer layers varies across the Tharsis region.

The measurements were taken while Mars Express was orbiting at an altitude of between 170 to 205 miles above the Tharsis volcanic "bulge," and were combined with data from NASA's Mars Reconnaissance Orbiter.

This bulge includes Olympus Mons, which is the tallest volcano in the Solar System, as well as three smaller Tharsis Montes that are evenly spaced in a row.

This area, according to an ESA press release, is thought to have been volcanically active until 100 to 250 million years ago.

The large mass of the volcanoes caused tiny "wobbles" in the trajectory of Mars Express as it flew overhead.  These wobbles were measured from Earth through radio tracking, and translated into measurements of density variations below the surface.

The high density of the volcanoes corresponds to a basaltic composition that is in agreement with other Martian meteorites that have fallen to Earth.

The new data reveals how the lava density changed during the construction of three Tharsis Montes volcanoes, including Arsia Mons, Pavonis Mons, and Ascraeus Mons.

They started with a lighter andesitic lava that can form in the presence of water, and were then overlaid with heavier basaltic lava that makes up the visible surface of the Martian crust, according to the ESA.

Mikael Beuthe of the Royal Observatory of Belgium and lead author of the paper published in the Journal of Geophysical Research, said that Arsia Mons is the oldest of the volcanoes, followed by Pavonis Mons and then Ascraeus Mons.

The density of the lava at Ascraeus Mons decreased at a later stage, so the top of the volcano is of lower density, Beuthe said in a press release.

This transition may reflect changes in heating beneath the surface in the form of a single mantle plume, which is an upwelling of abnormally hot rock from deeper within the viscous mantle.

This plume slowly moved sideways to create each of the three Tharsis Montes, according to the researchers.

This process is the opposite of Earth, where "plates" of crust move above a stationary plume to form chains of volcanoes.

The researchers also found lateral variations between Olympus Mons and the Tharsis Montes, with the three smaller volcanoes having a higher density underground "root" than Olympus Mons.

These roots, according to ESA, could be dense pockets of solidified lava or an ancient network of underground magma chambers.

“The lack of a high-density root below Olympus Mons indicates it was built on a lithosphere of high rigidity, while the other volcanoes partially sank into a less rigid lithosphere,” co-author Veronique Dehant, also of the Royal Observatory of Belgium, said. “This tells us that there were large spatial variations in the heat flux from the mantle at the time of their formation.”

Because the Tharsis Montes sit on top of the Tharsis bulge, compared to the Olympus Mons which sits on the edge, the greater crustal thickness at the center may have acted as an insulating life to increase the temperature.

“These results show that data on the Mars interior are key to understanding the evolution of the Red Planet,” Olivier Witasse, ESA Mars Express Project Scientist, said. “One option for a future mission to Mars would be a network of small landers, simultaneously measuring seismic activity in order to probe the interior.


Image 1: Olympus Mons color-coded according to height from white (highest) to blue (lowest), based on images captured by the High Resolution Stereo Camera (HRSC) on board ESA´s Mars Express. The new data find that Olympus Mons is built on a rigid lithosphere whereas the nearby Tharsis Montes partially sank into a less rigid lithosphere, suggesting that there were large spatial variations in the heat flux from the mantle at the time of their formation. Credits: ESA/DLR/FU Berlin (G. Neukum)

Image 2: Shaded relief image of Tharsis Montes and Olympus Mons derived from Mars Orbiter Altimeter data which flew on board NASA´s Mars Global Surveyor. The new data suggest that Tharsis Montes formed one by one, starting with Arsia Mons, possibly by the movement of a single mantle plume moving under the surface. Credits: NASA