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Recent geological activity on the Moon and Mars
Posted: 21 February 2012

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Marsquakes on the red planet and crustal stretching on the Moon show that planet Earth is not the only geologically active body in our local Solar System neighbourhood.

The largest of the newly detected graben found in the highlands of the lunar farside. The broadest example measures 500 metres across and could be up to 20 metres deep. Image: NASA/Goddard/Arizona State University/Smithsonian Institution.

New images from NASA’s Lunar Reconnaissance Orbiter (LRO) suggest that the Moon’s crust was being stretched as recently as 50 million years ago. Tiny valleys many times longer than they are wide were formed as the crust pulled apart, dropping down between two bounding fault lines. Known by geologists as graben, these features have been identified in a number of locations across the Moon, but the finding contradicts the signs of global contraction identified by LRO in 2010. By examining scarps – lobe-shaped cliffs – planetary scientists then estimated that the Moon had shrunk by about 100 metres since it formed over 4.5 billion years ago (read our story The Moon is shrinking, here).

“We think the Moon is in a general state of global contraction because of cooling of a still hot interior,” says Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington. “The graben tell us forces acting to shrink the Moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the Moon cannot be large, or the small graben might never form.”

This graphic illustrates how graben are formed when the lunar crust was stretched and pulled apart. Image: Arizona State University/Smithsonian Institution.

Meanwhile the HiRISE camera onboard the Mars Reconnaissance Orbiter has identified boulders lying along the young Cerberus Fossae fault system that were toppled from a cliff during ‘marsquakes’. MRO scientists compared the trails that the dislodged boulders made in the Martian soil with those made during earthquakes to arrive at this conclusion and found that the same patterns would not have been created if the boulders had been bound up in a glacier and were deposited as the ice melted, for example.

The boulders range in size from two to twenty metres across, and the size and number decrease over a radius of 100 kilometres from a central point along the Cerberus Fossae fault. “This is consistent with the hypothesis that boulders had been mobilized by ground-shaking, and that the severity of the ground-shaking decreased away from the epicenters of marsquakes,” says Gerald Roberts, an earthquake geologist at Birkbeck, University of London.

Scientists have found evidence of relatively recent quakes on the surface of Mars by studying boulders that fell off cliffs, leaving tracks behind. Image: HiRISE.

Since the Martian winds have not yet erased any traces of the boulder tracks the scientists conclude that the marsquakes were recent. Given that it can take just a few years for Martian winds to completely erase the tracks of Mars rovers in particularly exposed areas, it is possible that marsquakes are still occurring today. If that is the case, the Martian rumblings are likely driven by movements of magma within the mighty Elysium Mons volcano nearby. Such volcanic activity would produce enough heat to melt subsurface ice and perhaps even create habitats conducive for life.

The new LRO results will be published in the March issue of the journal Nature Geoscience and the MRO study will be published Thursday in the Journal of Geophysical Research-Planets.