MRO CTX Spots Dust Devils at Phoenix Landing Site
Captioned Image Release No. MSSS-30 — 6 May 2008
NASA’s Mars Scout mission, Phoenix, is scheduled to land on the martian northern plains near 68°N, 127°W, on 25 May 2008. In preparation for the landing, the Mars Reconnaissance Orbiter (MRO) Mars Color Imager (MARCI) and Context Camera (CTX) have been monitoring the weather in the region around the landing site. On 20 April 2008, the CTX camera captured a view showing two active dust devils within the Phoenix landing ellipse.
Three pictures are shown here. The first is a sub-frame of a CTX image, acquired at a resolution of 6 meters (19.7 ft) per pixel, which shows the two dust devils. Based on measurement of the shadows cast by the two dust devils, one of the vortices towered about 590 meters (~1930 feet) with a dust plume extending 920 meters (~3020 feet) above the surface. The other reached about 390 meters (~1280 feet) high, with a dust plume extending to 790 meters (~2590 feet).
The second picture is a regional view from the daily global mapping camera on MRO, the MARCI. The white ellipse is the location of the Phoenix landing site, and the white dot is the location at which CTX observed the two dust devils. The MARCI and CTX images were acquired simultaneously.
The third picture shows a reduced-scale view of the entire CTX image (processed somewhat differently) from which the first picture was extracted. CTX images usually cover an area 30 kilometers (18.6 miles) wide. This particular image not only covered 30 km in width, it covered an area of about 314 km (195 miles) in length. It shows various wind streaks formed by wind gusts prior to the day that the dust devils were observed.
When these CTX and MARCI images were acquired, the season was late Northern Spring (Spring will end and Summer will begin one month after the Phoenix landing, on 25 June 2008). A few weeks earlier, the landing site was still covered with seasonal frost left over from the previous winter. White patches in small craters near the center of the picture showing the dust devils are areas where the winter frost remained, even as late as 20 April.
As Spring gives way to Summer, dust devils are likely to occur more frequently, as local temperatures rise. These two dust devils observed in late April are among the first of the season. Four additional CTX images of the landing site have been taken since then, including two over the past weekend, but they did not show dust devils. After the landing, as Summer approaches, the cameras on the Phoenix lander might be able to spot additional dust devils, as has been the case at the Mars Exploration Rover (MER-A) Spirit landing site.
Dust devils are whirling vortices that have picked up dust from the ground. Such vortices can occur even when no dust is present, but then they are not visible to the cameras onboard the Mars Reconnaissance Orbiter. Such vortices commonly form as hot air rises from the surface on an otherwise generally calm day with little or no breeze. Dust devils will travel across the surface on the gentle breezes that do occur. Sometimes, dust devils have been observed by cameras orbiting Mars to create streaks on the ground as they disrupt and pick up dust (no streaks are observed in this CTX image).
The Mars Orbiter Camera (MOC) onboard the Mars Global Surveyor (MGS) observed dust devils—and streaks created by them—throughout its 1997 to 2006 mission. During that time, scientists at Malin Space Science Systems observed more than 12,000 active dust devils. They were seen over the full range of elevations and nearly all latitudes on Mars. Dust devil streaks were found in MOC images as far north as the edge of the north polar residual cap and the dune fields that surround the region. However, the northernmost active dust devil captured by the MOC was at 62.2°N, which is further south than the 68°N Phoenix site.
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Citation and Credit
Malin Space Science Systems (MSSS) built and operates the Mars Reconnaissance Orbiter (MRO) Mars Color Imager (MARCI) and Context Camera (CTX). MSSS also built and operated the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC). In addition, MSSS built the Mars Odyssey (ODY) Thermal Emission Imaging Spectrometer (THEMIS) Visible (VIS) camera subsystem, which shares optics with the thermal infrared instrument and is operated at Arizona State University (ASU). MSSS built the Mars Descent Imager (MARDI) for the Phoenix Mars Scout lander and in 2008 is designing a camera for the 2011 Juno Mission to Jupiter and is completing camera systems for the 2009 Mars Science Laboratory (MSL) rover mission and the 2008 Lunar Reconnassaince Orbiter (LRO).