The second largest volcano on the surface of Mars after Olympus Mons, and therefore the second largest in the Solar System, Arsia Mons is a part of the Tharsis Montes range of volcanoes which also include Pavonis Mons and Ascraeus Mons. It is a 9-kilometre-high shield volcano with a massive 120-kilometre-wide caldera, and one of the youngest volcanoes on Mars, with its most recent activity estimated at between 100-300 million years ago, which in Mars' geological terms is relatively new, especially as up to very recently it was thought that volcanic activity on Mars was a primordial process which had long ago ceased, leaving Mars a dead planet.

However, the relative lack of fresh impact craters within the caldera of Arsia Mons indicate not only that the volcano was active relatively recently (if Arsia Mons had been dead for billions of years as previously thought, then there would be a far higher number of impact craters from small meteorites), but also that there may be enormous deposits of ice beneath the caldera.

This new research was made possible by the Mars Global Surveyor satellite, which also revealed clouds of ice and water floating near Arsia Mons's flanks, adding to the growing evidence that there is a lot more water on Mars than we thought.


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