Mars may have once had an ocean so vast that it covered one-third of the planet before evaporating billions of years ago and leaving behind a telltale sign: a flat band of land, outlining the former ocean — similar to the ring left behind in a drained bathtub.
If confirmed by direct observations, this “coastal shelf,” as researchers call it, would contribute crucial evidence to a long-standing scientific debate, according to a study describing the new evidence. While dried-up river networks, deltas and lakebeds offer proof that Mars had a watery past, there is no consensus among experts on whether it also had a large ocean, which would have made Mars look much more similar to Earth than it does today.
