Larger Annotated Version
NASA's Phoenix Mars Lander is scheduled to land on the Martian northern
plains near 68 degrees north latitude, 127 degrees west longitude on May
25, 2008. In preparation for the landing, NASA's Mars Reconnaissance
Orbiter has been monitoring weather in the region around the landing site.
On April 20, 2008, the orbiter's Context Camera captured this view showing
two active dust devils within the Phoenix landing ellipse.
This is a subframe covering an area about 26 kilometers (16 miles) on each
side, part of a larger image posted at PIA10632. It shows two dust
devils and their shadows. Based on measurement of the shadows cast by the
dust devils, one of the vortices towered about 590 meters (about 1,930
feet) with a dust plume extending 920 meters (about 3,020 feet) above the
surface. The other reached about 390 meters (1,280 feet) high, with a dust
plume extending to 790 meters (2,590 feet). The resolution here is 6
meters (19.7 feet) per pixel.
When the Context Camera acquired this image, the season in Mars' northern
hemisphere was late spring. A few weeks earlier, the Phoenix 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 are areas
where the winter frost remained, even as late as April 20.
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. The cameras on the Phoenix
lander might be able to spot additional dust devils after the spacecraft
arrives, as the Mars Exploration Rover Spirit has been able to do at its
southern hemisphere 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, though no streaks are
observed in this image.
The Mars Orbiter Camera onboard NASA's Mars Global Surveyor orbiter
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 Mars Orbiter Camera 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 that camera was at 62.2 degrees north latitude, which is further south
than the Phoenix site.
Another camera on the Mars Reconnaissance Orbiter, the Mars Color
Imager, captured a simultaneous, wider-field, color view of the area
included in this Context Camera image. That view can be seen at PIA10634.
NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for
NASA's Science Mission Directorate, Washington. Lockheed Martin Space
Systems, Denver, is the prime contractor for the project and built the
spacecraft. Malin Space Science Systems, San Diego, provided and operates
the Context Camera and Mars Color Imager.
