Mars appears to be our twin in some ways—it is rocky, nearby, and of similar size. But after many a hopeful prodding, Mars remains a dead body. The rover Curiosity made a happy discovery last month, photographing river rocks in an ancient Martian streambed. This led Claire L. Evans to straighten out the legendary “canals” of Mars, popularized by astronomers such as Percival Lowell in the nineteenth century. Lowell’s carefully mapped waterways were much nearer than he thought—likely “projections of the vein structure of his own eyeball, a known nuisance among planetary observers using very high magnification.” No stranger to canals himself, Greg Laden writes “early research on Mars also suggested the possibility of ancient free water on the planet, and eventually, these suggestions panned out.” With a history of flowing water, could life on Mars have been far behind? Curiosity may soon have the answer.