Ares Vallis was the landing site of NASA's Mars Pathfinder spacecraft, which studied a region of the valley near the border with Chryse in 1997.

It has been argued that Uzboi, Ladon, Margaritifer and Ares valles, although now separated by large craters, once comprised a single outflow channel, flowing north into Chryse Planitia.

[2] The source of this outflow has been suggested as overflow from the Argyre Crater, formerly filled to the brim as a lake by channels (Surius, Dzigai, and Palacopus Valles) draining down from the south pole.

[3][4][5][6][7] Research, published in January 2010, suggests that Mars had lakes, each around 20 km (12 mi) wide, along parts of the equator.

Volcanoes would have released gases that thickened the atmosphere for a temporary period, trapping more sunlight and making it warm enough for liquid water to exist.