Astronomers have revealed dramatic new images of the largest volcano in the solar system.
They show a crumpled feature at the base of Mars' Olympus Mons, resulting from an ancient catastrophic landslide on the Martian surface.
Olympus Mons is a giant shield volcano 13.6 miles tall, 2.5 times higher than Mount Everest's height above sea level. The volcano was first spotted in 1971 by NASA's Mariner 9 spacecraft.
However, in the decades that followed, it became clear that there was something unusual about the volcano's lower flanks. Spreading out from its base astronomers saw an expanse of rough-textured rock, stretching for hundreds of miles.
At the edges of this geological halo, know as an aureole, lay a steep cliff face, reaching 26,000 feet tall in places. The unusual feature was named Lycus Sulci, but it has taken years of observation to work out how it was formed.
In a statement on August 23, the European Space Agency announced that this raggedy, steep terrain was likely the result of catastrophic landslides at the volcano's lower flanks millions of years ago.
"Large amounts of lava once flowed down the volcano, triggering landslides that tumbled down its flanks to meet bedrock…containing ice and water," ESA said.
"The swelteringly hot lava caused this ice to melt and become unstable; as a result, the rocky rim of Olympus Mons broke off and partially slid away," the agency said. "This collapse came in the form of huge rockfalls and landslides, which slipped downwards and spread widely across the surrounding plains."
As these landslides traveled across the Martian surface, they became alternately compressed and stretched, creating the characteristic wrinkles seen in the aureole. Over time, these ridges became even more prominent as wind swept across the planet's surface, scattering dust and sand along its peaks.
These conclusions have been made possible by imagery from ESA's Mars Express spacecraft and its in-built High Resolution Stereo Camera. The satellite has been orbiting the Red Planet since 2003 and has revealed extensive insights into the Martian surface.
The mission has also provided a more complete map of the chemical composition of the Martian atmosphere and traced the history of water across the planet, providing tantalizing clues into the prehistoric conditions of our next-door neighbor and its potential capacity for supporting ancient life.
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