The Floor of Niger Vallis: Bearer of Ancient Floodwaters?

This image shows a portion of the floor of Niger Vallis, an ancient Martian
outflow channel.  Niger Vallis originates on the flanks of the volcano
Hadriaca Patera, and empties into the Hellas impact basin.  Outflow channels
are observed in many regions of the planet, and may have been carved by brief
eruptions of liquid water from beneath the surface.  Since Niger Vallis
formed, impacts have cratered the channel floor, and fine-grained wind-blown
debris has been transported across the surface, eroding and burying all but
the freshest craters.  The curved ridge in the scene may be the remnant of a
large crater rim.  At the high resolution of this image, a pattern of
parallel dunes and ripples can be seen, as well as individual boulders as
large as two meters across.

Images from the High Resolution Imaging Science Experiment and additional
information about the Mars Reconnaissance Orbiter are available online at: 
http://www.nasa.gov/mro or http://HiRISE.lpl.arizona.edu.

For information about NASA and agency programs on the Web, visit:
http://www.nasa.gov.

JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Reconnaissance Orbiter for NASA's Science Mission
Directorate, Washington. Lockheed Martin Space Systems is the prime
contractor for the project and built the spacecraft. The HiRISE camera was
built by Ball Aerospace Corporation and is operated by the University of
Arizona.