Mars is a quiet world. Stiff breezes can stir up big dust storms, and chunks of space rock occasionally gouge holes in its crust, but otherwise not much happens.
That wasn't always the case, though. In the distant past, rain fell from the sky, and rivers carved deep canyons. And giant volcanoes poured lava onto the surface, building mountains that are miles high.
The largest and youngest are in a region known as Tharsis Ridge. The biggest of the bunch, Olympus Mons, is as big as Missouri. There's evidence that it's been active within the last few million years -- and perhaps even the last few thousand.
A second group of volcanoes is a quarter of the way around the planet, on the Elysium Ridge. The largest of its three volcanoes is Elysium Mons. It's about 250 miles across, and it towers eight miles above the surrounding plains. It has a steeper slope than Olympus Mons, so it might be a good target for mountain climbers.
Elysium Mons is probably older than Olympus Mons. There are no recent lava flows on its flanks, and it's pockmarked by more impact craters. That indicates that the volcano has been quiet for several hundred million years.
Mars is in good view early tomorrow. It's just a little below the Moon as they rise around 1 or 2 o'clock. It looks like a fairly bright orange star. Mars and the Moon will be at their closest at first light, when they'll stand high in the south.
More about Mars and the Moon tomorrow.
Script by Damond Benningfield, Copyright 2009
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