Mars Express uncovers megaflood landscape hinting at an ancient Martian ocean

ESA’s Mars Express reveals a hundreds-of-miles-long, several-miles-wide, and over-a-thousand-feet-deep channel in Shalbatana Vallis with chaotic terrain and layered deposits, strengthening the case that episodic floods fed a northern ocean on Mars. While the data support a pulsed-ocean scenario with water periodically releasing from subsurface ice, the debate over whether the ocean was long-lived or episodic remains unsettled.