<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><div style="margin: 0px; font-size: 12px; "></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(2, 30, 170); "><span style="text-decoration: underline ; letter-spacing: 0.0px"><a href="http://www.nasa.gov/mission_pages/MRO/multimedia/pia16715.html">Full image and caption<span style="letter-spacing: 0px; "></span></a></span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); "><span style="letter-spacing: 0.0px; color: #000000">"</span><span style="letter-spacing: 0.0px">PASADENA, Calif. -- Researchers using NASA's Mars Reconnaissance Orbiter see seasonal changes on far-northern Martian sand dunes caused by warming of a winter blanket of frozen carbon dioxide. </span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); "><span style="letter-spacing: 0.0px">Earth has no naturally frozen carbon dioxide, though pieces of manufactured carbon-dioxide ice, called "dry ice," sublime directly from solid to gas on Earth, just as the vast blankets of dry ice do on Mars. A driving factor in the springtime changes where seasonal coverings of dry ice form on Mars is that thawing occurs at the underside of the ice sheet, where it is in contact with dark ground being warmed by early-spring sunshine through translucent ice. The trapped gas builds up pressure and breaks out in various ways. </span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); "><span style="letter-spacing: 0.0px">Transient grooves form on dunes when gas trapped under the ice blanket finds an escape point and whooshes out, carrying out sand with it. The expelled sand forms dark fans or streaks on top of the ice layer at first, but this evidence disappears with the seasonal ice, and summer winds erase most of the grooves in the dunes before the next winter. The grooves are smaller features than the gullies that earlier research linked to carbon-dioxide sublimation on steeper dune slopes. </span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); "><span style="letter-spacing: 0.0px">Similar activity has been documented and explained previously where seasonal sheets of frozen carbon dioxide form and thaw near Mars' south pole. Details of the different northern seasonal changes are newly reported in a set of three papers for the journal Icarus. A video showing some of the changes is online at <a href="http://www.nasa.gov/multimedia/videogallery/index.html?media_id=158896871"><span style="letter-spacing: 0px; color: rgb(2, 30, 170); ">http://www.nasa.gov/multimedia/videogallery/index.html?media_id=158896871</span></a> . </span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; color: rgb(47, 47, 47); "><span style="letter-spacing: 0.0px">The findings reinforce growing appreciation that Mars today, however different from its former self, is still a dynamic world, and however similar to Earth in some respects, displays some quite unearthly processes.</span><span style="letter-spacing: 0.0px; color: #000000">"</span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; "><span style="letter-spacing: 0.0px"><b>MARS RECONNAISSANCE ORBITER HIRISE IMAGES</b></span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; "><span style="letter-spacing: 0.0px">All of the HiRISE images are archived here: <a href="http://hirise.lpl.arizona.edu/"><span style="letter-spacing: 0px; color: rgb(4, 51, 255); ">http://hirise.lpl.arizona.edu/</span></a>.</span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; "><span style="letter-spacing: 0.0px">More information about the MRO mission is available online at <a href="http://www.nasa.gov/mro"><span style="letter-spacing: 0px; color: rgb(4, 51, 255); ">http://www.nasa.gov/mro</span></a>.</span></div><div style="margin: 0px; font-size: 12px; font-family: Arial; min-height: 14px; "><span style="letter-spacing: 0.0px"></span><br></div><div style="margin: 0px; font-size: 12px; font-family: Arial; "><span style="font-family: Helvetica; "></span></div></body></html>