If you remember back to March you may remember that I mentioned the discovery, with THEMIS on Mars Odyssey, of possible open-top caves on the flanks of Arsia Mons. THEMIS had a resolution of about 18m in the images. Now (via Cumbrian Sky via Emily's Planetary Blog) a new image from the HiRISE instrument on Mars Reconnaissance Orbiter shows one of those proposed cave entrances with a full resolution of 25cm per pixel!
Possible cave entrance on the flank of Arsia Mons, Mars CREDIT: NASA / JPL / U. Arizona
I must admit that these big holes sent my mind back a few years to the time I read First Men in the Moon by H.G. Wells. In that story, the main characters find an alien race (Selenites) living below the surface of our Moon. The beings had huge shafts connecting them to the surface that were covered in lids during the lunar night but let creatures called mooncalves out during the lunar day. I'm not saying that this hole is inhabited now, but for future Martian settlers, building your base underground may be a handy way to protect against harmful cosmic rays.