Mars May Have Had a Vast Ancient Ocean, Traced by Canyon Deltas

Researchers using data from ESA's ExoMars Trace Gas Orbiter, Mars Express, and NASA's Mars Reconnaissance Orbiter modeled a former sea level in Coprates Chasma (within Valles Marineris) and identified delta-like structures matching Earth river mouths, suggesting a large ancient Martian ocean at least as big as Earth's Arctic Ocean during a period of abundant surface water; this supports the idea of a once-habitable Mars, though implications for life remain uncertain.