Even with the sun high in the sky, this collapse pit on a Martian lava plain is so deep that even the super-sensitive Mars Reconnaissance Orbiter cannot see the bottom. On Earth, openings like this one often lead to extensive cave networks, and on Mars, such a place could shelter life, or even future astronauts. Learn more.

Sent by: Mars Reconnaissance Orbiter | From: Mars | Released: October, 2008 | Credit: NASA/JPL/UA | Image source