Imagery from the recent Messenger flyby seem to indicate lava once flowed on the planet's surface. Considering how close the thing is to the Sun, I'm surprised lava can cool. Then again, I'm (quite obviously) no geologist, so most likely I'm misunderstanding how lava works.
IIRC, the sunward side of Mercury is damnably hot. The rest of see a very cold side. That being said, the damnably hot side is still cooler than molten rock, so it could flow and cool. It'd just take a lot longer on the sunward side than the cold side.
Posted by: Ron on January 22, 2008 11:21 AM