DUNES & LAYERED ROCKS
Red Planet geological features pose for NASA’s MRO lens. Pictures taken by HiRISE tool
The layered bedrock in this image (left) was brought from several kilometers of depth during the formation of this 44 kilometer wide crater in the volcanic plains of Mars' Lunae Planum.
As these layers were exhumed and brought to nearly vertical orientations, faulting and fracturing occurred and breccia dikes formed. Breccias are rocks consisting of angular and sharp fragments, and a dike is a fracture that has been widened by forces pulling apart the rock while simultaneously filling it with rocky materials. Breccia dikes are a common feature in terrestrial craters and can now be recognized in brilliant preservation on Mars.
This high-resolution, false-color image cutout above allows us to see a cross-cutting breccia dike near the bottom of the image.
The large dark feature is a classic Martian sand dune (right). Most sand on Earth is made from the mineral quartz, which is white and bright. On Mars, most sand is composed of dark basalt, a volcanic rock. For this reason, dunes on Mars are darker than those on Earth.
The dunes in this observation, within Wirtz Crater, are known as barchans. The steepest slope is on the eastern (right) side, partially in shadow, and represents the direction the dune is migrating as the sand is blown and transported by the wind. Small ripples are visible on much of the dune surface.
The dark streaks on the dune are tracks left by passing vortices known to us as dust devils. These raise dust off the dune, revealing a darker substrate.
Both pictures were taken by HiRISE (High Resolution Imaging Science Experiment), a tool of the MRO (Mars Reconnaissance Orbiter) spacecraft.
One of the main instruments on board the spacecraft, SHARAD (SHAllow RADar), has been developed in Italy and provided to NASA by the Italian Space Agency as a Facility Instrument.