Meteorite-Triggered Floods on Mars

Present day Mars is cold and dry with water mostly locked up as ice in the polar caps or in the subsurface. Abundant evidence, in the form of dry valleys, channels, deltas, and lake beds, exists for water having flowed and ponded on the surface of the planet in the distant past, typically more than a few billion years ago. There are examples of more “recent” (i.e., 1-3 billion years) lesser amounts of more localized surface drainage, sometimes occurring as channel-carved deposits of rocks and debris called alluvial fans that are much like those flanking mountains in the desert southwest of the United States. However, there are also examples of large-scale valleys and channels around some large impact craters whose formation and activity appears to vary but indicates tremendous discharges of water that largely postdate the ancient period of widespread water flow on the Red Planet. 

Two examples of drainage forms around craters are found around the 125 by 150 km-in diameter (~78-93 miles-in diameter) Hale crater in the northern Argyre region and on the western side of the ~90 km-in-diameter (~56 miles-in-diameter) Jones crater in Margaritifer Terra region of Mars. Both craters are relatively pristine, but Hale crater probably formed around one billion years ago, whereas Jones crater is older and formed roughly 2 to perhaps 3.5 billion years ago. Around Hale crater, pristine water-carved features are of a scale suggesting enormous water discharge rivaling that of the Amazon River on the Earth, but that was quite short-lived, probably lasting only for a period of weeks. Around Jones crater, relatively pristine valleys and interior channels are also well-preserved, large scale, and appear to have formed over a period of weeks to no more than months to years. The water-carved features and deposits around both craters are especially well-preserved and their formation post-dated other water-carved valleys in the surrounding regions.

It is likely that the formation of the valleys and channels around Hale and Jones was caused by the impact of the large meteorites that formed the craters. There is tremendous amount of heat released during such large impact events that would have melted any ice present in and between the rocks where the impacts occurred. Resultant water would have flowed down hill, carving the fresh appearing valleys and channels and ponding in local basins. The duration and magnitude of the water flow would have depended on the amount of ground ice present and able to be melted during the impact and how quickly the heat from the impact was dissipated from the near surface, thereby causing any remnant water to refreeze. 

Impact-caused melting and short-lived drainage relatively late in Mars history stands in contrast to the more widespread and longer-lived flow of water earlier in the planet’s history. Nevertheless, the large volumes of water associated with at least the Hale and Jones crater events suggests that the impacts created potentially habitable environments occurring relatively late in Martian history.