Mysterious White Cloud Hangs Over Martian Volcano

Last month, the European Space Agency's Mars Express orbiter spotted a white cloud suspended over the western slope of Arsia Mons, an enormous volcano near the red planet's equator. The 930-mile-long cloud looks like the kind of volcanic plumes huffed out by Earth's active volcanoes -- but it's not; 'Arsia Mons is long extinct -- its last eruption is estimated to have occurred around 50 million years ago,' reports Motherboard. From the report: The volcano still plays a role in shaping the water-ice cloud, though, along with atmospheric dust levels and the Martian seasons. With its 12-mile-high peak and diameter of nearly 400 miles, Arsia Mons is 30 times more voluminous than the largest volcanoes on Earth. Its humongous bulk condenses and cools air currents as they pass over the summit, creating this âoeorographic cloudâ -- a nephologic formation that tend to form over leeward (downwind) slopes -- on the western flank of the volcano.

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