A map of the planet Mars and its putative “canals,” produced by the astronomer Percival Lowell for the October 1894 issue of Scientific American. Already, a growing pile of evidence suggests ancient Mars could very well have been an inhabited planet—and may still be. If it’s not so crazy to imagine that ancient Mars was a biological world, then maybe “life” isn’t such an extraordinary claim after all. “If we only let something’s rareness guide us to life, we may miss a lot of life that is just ordinary life, and we may be drawn to extraordinary nonbiological processes and think they’re life instead.” But a partial solution to Viking’s Mars life conundrum turned up unexpectedly in 2008.