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"My name is Emily Lakdawalla -- I'm the senior editor and planetary evangelist for the Planetary
Society." What are the hollows on Mercury?
"Well, the Messenger mission has been mapping and orbiting Mercury and they've discovered
these new kinds of features that nobody had ever seen before that they were calling hollows
-- they're these pits in the ground, but they're not impact craters. They look like somewhere
where something has evaporated. They look like Swiss cheese -- like that terrain at
the south pole of Mars where the carbon dioxide cap is evaporating. They look kind of the
same, except that this is mercury -- there's no carbon dioxide or water ice. It's all gotta
be solid rock." "So what exactly is evaporating to create
these holes and how it's disappearing from the ground is still a complete mystery. And
the Messenger missions -- they're following up on the high-resolution imaging, but they
still don't have good info for what those hollows are."
Are they similar to the caves on the Moon and Mars?
"The caves that have been found on the moon and Mars are likely skylights into lava tubes.
There's vulcanism all over the solar system -- that's how most of the surfaces of most
of the surfaces of most of the planets were built -- with lava spewing out. And wherever
you have lava, you've got often a solid surface on the top and then liquid lava running underneath
the surface. Eventually that drains and you get a hollow tube, and then maybe an earthquake
happens or something opens a skylight down into the tube. So we've found cave skylights
on both the moon and Mars, and of course on Earth.
I don't know that we've found any of these on Mercury -- I don't think we have."
Read more: http://www.universetoday.com/110721/what-are-these-hollows-on-mercury/#ixzz2x5gU7ThX