| This pair of images shows a dune as it appeared on July 17, 2002, (left) and as it appeared on April 27, 2005, (right). During this period, a couple of gullies formed on the dune slip face. It is critical to recognize that the 2002 image was obtained at a time of year when the incident sunlight was coming in from a lower angle, relative to the horizon, than in the 2005 image. If the gullies had been present in 2002, their appearance would be sharper and more pronounced than they are in the 2005 image. The gullies simply did not exist on July 17, 2002. Image credit: NASA/JPL/MSSS/ASU |
