Sunday, May 29, 2011

Nili Patera Dunes

Individual sand dunes are visible in this image of Nili Patera.

Photo credit: NASA/JPL/Arizona State University

Note: This photo is almost identical to this one, this one, and this one.

Saturday, May 28, 2011

Clouds over Olympia Undae

Clouds are common near the north polar cap throughout the spring and summer. The clouds typically cause a haze over the extensive dune fields. This VIS image shows the edge of the cloud front.

Photo credit: NASA/JPL/Arizona State University

Notes: These dunes are located in Olympia Undae north of Dokka Crater. Also, the above photo is identical to this one.

Spirit, Spirit, Shining Bright

This observation catches the NASA Mars Exploration Rover Spirit gleaming in the sun beside Home Plate inside Gusev Crater. It also catches a dust devil in action.

We were surprised to see that the Spirit rover itself is the brightest spot in the image, unlike dozens of previous images of both rovers. Analysis of the illumination and viewing geometry and the tilt of the rover indicate that, by accident, we imaged it near the specular point for the flat solar panels. The specular point is where the illumination angle is the same as the viewing angle, and the vectors are aligned.

Ground-based measurements prior to launch showed that the specular reflection could be seen even when there is a thin dust cover over the panels. This result does show that the solar panels are not covered by an optically thick layer of dust (i.e., too thick for any light to pass through it). Spirit last communicated on 22 March 2010.

And a Dust Devil to Boot
Scientists have been coming to realize that dust devils on Mars are far more common that had been thought. Dust devils look like mini tornadoes and are made up of swirling vortices of air that pick up very fine pieces of dust (the smallest particles of soil, much finer than a grain of sand). They are also an important part of the Martian climate and geology.

Each year myriads of dust devils crisscross the surface scouring up loose dust. By removing dust the dust devils also, in effect, clean the surface. Since a dusty surface tends to be brighter and reflect sun light, dust devils collectively darken the surface and cause more sun light to be absorbed and warm the soil surface and the air. Dust devils can also kick lots of dust into the air where the dust can absorb sun light passing through the atmosphere, thus warming the atmosphere more directly.

Many images show tell-tale dark streaks that crisscross and wiggle all over the surface. The high wind speeds of dust devils can also shift and move sand that otherwise would remain in one location. By moving surface soil grains around, dust devils can serve to mix different minerals from various locations.

Photo credit: NASA/JPL/University of Arizona

Friday, May 27, 2011

Nili Patera Dunes

The dunes in this VIS image are located in Nili Patera, one of the two patera of Syrtis Major Planum.

Photo credit: NASA/JPL/Arizona State University

Note: If you click on the Nili Patera label, you'll notice that there are a number of photographs that are of the same landscape (more or less). Why would the THEMIS scientists keep taking pictures of the same ground over and over? I can think of three reasons off-hand: 1) doing so allows the scientists to monitor the ground for any fresh features, such as newly formed impact craters, 2) the scientists can monitor whether or not the wind is pushing the sand dunes along or not and, if so, how quickly the dunes are moving, and 3) because the photos are not exactly covering the same area, a larger mosaic of the area can be made at (more or less) the same resolution.