Free Astronomy Magazine May-June 2018

10 MAY-JUNE 2018 PLANETOLOGY Reconnaissance Orbiter. Curiously, one of the most fa- mous lunar skylights, the circular one visible in Marius Hills, has dimensions comparable to those of a famous elongated martian skylight visible in the region of Pavo- nis Mons: the former is 65 meters wide and 80 meters deep; the latter is 190×160 meters wide and at least 115 meters deep. We do not know how long the lava tubes connected to these and other skylights are, and we also do not know if they are empty for long distances or if, H iRISE image of a lava tube sky- light entrance on the martian volcano Pavonis Mons (top), and HiRISE image of a 180 m wide lava tube skylight on the southeast flank of Pavonis Mons (right). [NASA/JPL/Calthech]