Mar. 13, 2010 New studies of ripples and dunes shaped by the
winds on Mars testify to variability on that planet, identifying
at least one place where ripples are actively migrating and
another where the ripples have been stationary for 100,000 years
or more. Patterns of dunes and the smaller ripples present some
of the more visually striking landforms photographed by cameras
orbiting Mars. Investigations of whether they are moving go back
more than a decade. Two reports presented at the 41st Lunar and
Planetary Sciences Conference near Houston recently make it
clear that the answer depends on where you look. Both reports
used images from the High Resolution Imaging Science Experiment
(HiRISE) camera on NASA's Mars Reconnaissance Orbiter, which
allows examination of features as small as about a meter, or
yard, across. One report is by Simone Silvestro of the
International Research School of Planetary Sciences at Italy's
G. d'Annunzio University, and his collaborators. They
investigated migration of ripples an