A huge geological structure on Mars resembling a bathtub ring may be evidence of an ocean that once covered a third of the Red Planet's surface, a new study finds. Decades of previous research have suggested that although Mars is now famously the "Red Planet," it once possessed liquid water on its surface. However, it remains uncertain whether that water was limited to lakes and streams, or if there was enough to form long-lasting oceans. Solving this mystery could shed light on whether ancient Mars once hosted life as we know it. In the new study, researchers instead searched for other geological features that might serve as signs of lost Martian oceans . Using computer simulations, they essentially dried up Earth's oceans to see which details remained. The scientists discovered the most distinct feature of Earth's oceans, besides their water, are flat bands of land up to several hundred miles wide and ranging in elevation from about 50 to 1,345 feet (15 to 410 meters) below sea level.…