We talk a lot about Mars being dry, but that doesn’t mean it doesn’t have water: It means there’s no liquid water to be found. Instead, it’s in the form of ice.  There are millions of cubic kilometers of water ice frozen at the Martian poles . Small asteroid impacts have revealed water ice just below the surface at mid-latitudes , too; the impact excavates material from below, exposing the ice.  The equatorial regions have been more of a mystery. It’s cold enough in most spots there, especially below the surface, to support long-term water ice. But is it there? The answer is no, at least not in one spot in western Elysium Planitia. That’s a large flat region on the equator where NASA’s Mars InSight lander touched down.…