J. Geophys. Res. http://doi.org/q2g (2014)

Credit: © NASA/JPL/UNIVERSITY OF ARIZONA

The incision of shallow valleys, presumably by liquid water, at the martian mid-latitudes at a time when the climate is thought to have been cold and dry is enigmatic. Analysis of spacecraft imagery suggests that the valleys were carved by short-lived hydrological systems that developed beneath ice over 100 million years ago.

Daniel Hobley at the University of Virginia, USA, and colleagues analysed the geomorphology of two networks of valleys at the martian mid-latitudes, using images and data collected by the Mars Reconnaissance Orbiter, Mars Express and Mars Global Surveyor spacecraft. They found that the valleys are morphologically similar in the two regions and that both networks formed about 100 million years ago. Curiously, many of the valleys seem to have been formed by water flowing uphill. The researchers propose that the valleys were carved by water flowing beneath regionally extensive ice cover that was at least tens of metres thick. Such a scenario would permit the pressurized flow of water against the topographic gradient, similarly to water in a pipe.

The valleys may have formed rapidly during a single episode of ice melt, consistent with a short-lived period of climate warming.