Curiosity Finds An(other) Alien Visitor on Mars

The Curiosity rover has been on Mars since Aug. 6, 2102. In the more than four years it's been there, it's seen wonders beyond our Earthly reckoning: evidence of ancient flowing water, evidence of ancient standing water, methane in the atmosphere now, carbon in the rocks, dark basaltic sand dunes, weird lumpy moons circling a dusty red planet. Mars is indeed an alien world. But even with all that, sometimes Curiosity still manages to find things on Mars that are able to surprise and delight: The...