Sand Dunes on Mars, NASA/JPL-Caltech/University of Arizona: NASA's Mars Reconnaissance Orbiter Dec 28 2009

Dunes of sand-sized materials have been trapped on the floors of many Martian craters. This is one example, from a crater in Noachis Terra, west of the giant Hellas impact basin.

The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter captured this view on Dec. 28, 2009.

The dunes here are linear, thought to be due to shifting wind directions. In places, each dune is remarkably similar to adjacent dunes, including a reddish (or dust colored) band on northeast-facing slopes. Large angular boulders litter the floor between dunes.

The most extensive linear dune fields know in the solar system are on Saturn's large moon Titan. Titan has a very different environment and composition, so at meter-scale resolution they probably are very different from Martian dunes.

This image covers a swath of ground about 1.2 kilometers (three-fourth of a mile) wide, centered at 42.7 degrees south latitude, 38.0 degrees east longitude. It is one product from HiRISE observation ESP_016036_1370. The season on Mars is southern-hemisphere autumn. Other image products from this observation are available at http://hirise.lpl.arizona.edu/ESP_016036_1370.

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, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft.

Rainy Day at Hotei Arcus, Titan a Satellite of Saturn, Cassini Spacecraft May 21 2009

Complex and unique canyon systems appear to have been intricately carved into older terrain by the ample flow of liquid methane rivers on Saturn's moon Titan, as seen in this radar image taken by NASA's Cassini spacecraft on May 21, 2009.
The channels seen here indicate that fluids flowed from high plateaus on the right to lowland areas on the left. In the center of the image, the wide distribution of the channels' tributaries suggests that rainfall is effectively eroding the surface. The bright terrain toward the bottom of the image is interpreted as high cliffs and broken bedrock.
These canyon systems remind us that Titan is (or has recently been) a dynamic world with a complicated geological history. Multiple channels have flowed into a wide, dark arc in the center of this mountainous region. Here, the canyons appear to have been filled by fine-grained materials that appear dark (smooth) to Cassini's synthetic aperture radar. These canyon-filling materials were later carved by a large river channel that winds from the bottom left of the image toward the left center.
The image center is at 71 degrees south latitude, 240 degrees west longitude, and its dimensions are 335 by 289 kilometers (208 by 179 miles). The radar illuminated this area from the top of the image at 18 degrees incidence angle. The areas seen here are typical of other regions observed near Titan's south pole in other flybys

A short but fierce "gullywasher" rainstorm of methane falls on the mountains surrounding the intriguing flows of Titan's Hotei Arcus in this artist's concept by Michael Carroll, based upon radar mapping data from the Cassini spacecraft in orbit around Saturn.
Radar data show that the arc of Hotei is the boundary between rugged mountains to the south and east and a broad valley. Emerging from the mountains are several radar-bright channels that are likely now dry river beds that were carved by flowing methane due to rainfall. Within the valley, the channels end near lobate (blobby) flows some 100 to 200 meters (300 to 600 feet) thick, which some scientists think could be slushy ice lava from cryovolcanoes. These flows are portrayed here as the rough and elevated lighter tan areas in the foreground. It is possible that such phenomena could release methane from beneath the surface, helping to explain how Titan's atmosphere sustains its supply of methane.
The area depicted is located at approximately 28 degrees south latitude and 78 degrees west longitude.