When I first saw this image, I thought it was some kind of joke, or Photoshop trick. But nope, this is real. NASA’s Mars Reconnaissance orbiter has returned images of strange cavern entrances on Mars.
See that dark spot in the middle of the picture? It seems to be a hole, in an otherwise smooth landscape of lava. It isn’t an impact crater because it lacks a raised rim or ejecta. Light from the Sun must be getting down there, but it’s so deep that none of it is bouncing back out. It’s just a dark hole.
So what is it? Scientists think it’s some kind of chamber with a collapsed roof, or pit with extremely vertical sides. Whatever the case, it’s quite surprising to see.
And just in case you think this is an anomaly, there are actually 7 of these features discovered on Mars so far.
The Planetary Society’s Emily Lakdawalla has more details.