The new radar data offer support—but not incontrovertible ground truth—for the long-held vision of an expansive body of water covering the Martian north. "The ancient ocean hypothesis will take awhile to prove to a high scientific standard, because it's a bit buried, so to speak, today," Schörghofer says. And one can always wonder about additional interpretations of the radar echoes, which provide a relatively nonspecific diagnosis of a given material. All the same, "it's another piece of evidence for an ancient ocean," he says. "I'm starting to believe it."