Investigating Mars: Olympia Undae

This VIS image highlights the dune form/dune density aspects of Olypmia Undae. In the center there is a brighter, diagonal region of few dunes. These dunes are the arc or crescent shape of barchan dunes. As more sand becomes available the barchan dunes begin to merge into transverse dunes. The region of dunes surrounding the bright swath still have the underlying surface visible, and the transverse dunes have a lace-like layout. In the regions with a significant abundance of sand have developed the tightly packed transverse dunes with the wave-like distribution. Olympia Undae is a vast dune field in the north polar region of Mars. It consists of a broad sand sea or erg that partly rings the north polar cap from about 120° to 240°E longitude and 78° to 83°N latitude. The dune field covers an area of approximately 470,000 km2 (bigger than California, smaller than Texas). Olympia Undae is the largest continuous dune field on Mars. Olympia Undae is not the only dune field near the north polar cap, several other smaller fields exist in the same latitude, but in other ranges of longitude, e.g. Abolos and Siton Undae. Barchan and transverse dune forms are the most common. In regions with limited available sand individual barchan dunes will form, the surface beneath and between the dunes is visible. In regions with large sand supplies, the sand sheet covers the underlying surface, and dune forms are found modifying the surface of the sand sheet. In this case transverse dunes are more common. Barchan dunes "point" down wind, transverse dunes are more linear and form parallel to the wind direction. The "square" shaped transverse dunes in Olympia Undae are due to two prevailing wind directions. The density of dunes and the alignments of the dune crests varies with location, controlled by the amount of available sand and the predominant winds over time. The Odyssey spacecraft has spent over 15 years in orbit around Mars, circling the planet more than 71,000 times. It holds the record for longest working spacecraft at Mars. THEMIS, the IR/VIS camera system, has collected data for the entire mission and provides images covering all seasons and lighting conditions. Over the years many features of interest have received repeated imaging, building up a suite of images covering the entire feature. From the deepest chasma to the tallest volcano, individual dunes inside craters and dune fields that encircle the north pole, channels carved by water and lava, and a variety of other feature, THEMIS has imaged them all. For the next several months the image of the day will focus on the Tharsis volcanoes, the various chasmata of Valles Marineris, and the major dunes fields. We hope you enjoy these images! Orbit Number: 13238 Latitude: 80.7247 Longitude: 173.91 Instrument: VIS Captured: 2004-12-08 09:25 https://photojournal.jpl.nasa.gov/catalog/PIA22296