Mars – dusty, dry, and desert-clad – was once so rich in water it had not just lakes, but oceans, according to a new study. Observations using ground-penetrating radar have revealed underground features consistent with beaches on the red planet, 4 billion years ago. It's some of the best evidence to date that Mars was once so soggy as to host a northern sea. The research team has named that sea Deuteronilus. "We're finding places on Mars that used to look like ancient beaches and ancient river deltas," says geologist Benjamin Cardenas of The Pennsylvania State University. "We found evidence...