A River Ran Through it (3.5 Billion Years Ago)
New astonishing pictures by the European Space Agency have revealed a 1,500km long and 7km wide river that once ran across Mars. The agency’s Mars Express imaged the striking upper part of the remnants of Reull Vallis river on Mars with its high-resolution stereo camera, ESA said.
Reull Vallis, is believed to have formed when running water flowed in the distant martian past, cutting a channel through the Promethei Terra Highlands before running on towards the floor of the vast Hellas basin. This structure, which stretches for almost 1,500 km, is flanked by numerous tributaries, one of which can be clearly seen cutting in to the main valley towards the upper (north) side.