AEOLIAN BEDFORMS ON MARS

FROM:  NASA 

Sandy landforms formed by the wind, or aeolian bedforms, are classified by the wavelength--or length--between crests. On Mars, we can observe four classes of bedforms (in order of increasing wavelengths): ripples, transverse aeolian ridges (known as TARs), dunes, and what are called “draa.” All of these are visible in this Juventae Chasma image. Ripples are the smallest bedforms (less than 20 meters) and can only be observed in high-resolution images commonly superposed on many surfaces. TARs are slightly larger bedforms (wavelengths approximately 20 to 70 meters), which are often light in tone relative to their surroundings. Dark-toned dunes (wavelengths 100 meters to 1 kilometer) are a common landform and many are active today. What geologists call “draa” is the highest-order bedform with largest wavelengths (greater than 1 kilometer), and is relatively uncommon on Mars. Here, this giant draa possesses steep faces or slip faces several hundreds of meters tall and has lower-order superposed bedforms, such as ripples and dunes. A bedform this size likely formed over thousands of Mars years, probably longer. This image was acquired by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter on Jan. 6, 2014. The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for the NASA Science Mission Directorate, Washington. > More information and image products.  Image Credit-NASA-JPL-University of Arizona Caption: Matthew Chojnacki.

THE "v" DUNES OF MARS

FROM:  NASA

Migratory birds and military aircraft often fly in a V-shaped formation. The “V” formation greatly boosts the efficiency and range of flying birds, because all except the first fly in the upward motion of air -- called upwash -- from the wingtip vortices of the bird ahead.

In this image of a dune field on Mars in a large crater near Mawrth Vallis, some of the dunes appear to be in a V-shaped formation. For dune fields, the spacing of individual dunes is a function of sand supply, wind speed, and topography. This image was acquired by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter on Dec. 30, 2013. The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for the NASA Science Mission Directorate, Washington. > More information and image products Image Credit-NASA-JPL-Caltech-Univ. of Arizona Caption-Alfred McEwen

DUNE: AUSTRALIA

FROM: NASA
Great Sandy Desert, Australia

In northwest Australia, the Great Sandy Desert holds great geological interest as a zone of active sand dune movement. While a variety of dune forms appear across the region, this astronaut photograph features numerous linear dunes (about 25 meters high) separated in a roughly regular fashion (0.5 to 1.5 kilometers apart). The dunes are aligned to the prevailing winds that generated them, which typically blow from east to west. Where linear dunes converge, dune confluences point downwind. When you fly over such dune fields—either in an airplane or the International Space Station—the fire scars stand out. Where thin vegetation has been burned, the dunes appear red from the underlying sand; dunes appear darker where the vegetation remains.

Astronaut photograph ISS035-E-9454 was acquired on March 25, 2013, with a Nikon D3S digital camera using a 400 millimeter lens, and is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center. The image was taken by the Expedition 35 crew. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed. Image Credit: NASA