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Subimage #1
Figure 1 |
Subimage #2
Figure 2 |
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Anaglyph
Figure 3 |
Subimage #3
Figure 4 |
At the very beginning of spring in the southern hemisphere on Mars the
ground is covered with a seasonal layer of carbon dioxide ice. In this
image there are two lanes of undisturbed ice bordered by two lanes
peppered with fans of dark dust.
When we zoom in to the subimage (figure 1), the fans are seen to be pointed in
the same direction, dust carried along by the prevailing wind. The fans
seem to emanate from spider-like features.
The second subimage (figure 2) zooms in to full HiRISE resolution to reveal the
nature of the "spiders." The arms are channels carved in the surface,
blanketed by the seasonal carbon dioxide ice. The seasonal ice, warmed
from below, evaporates and the gas is carried along the channels. Wherever
a weak spot is found the gas vents to the top of the seasonal ice,
carrying along dust from below.
The anaglyph (figure 3) of this spider shows that these channels are deep, deepening
and widening as they converge. Spiders like this are often draped over the
local topography and often channels get larger as they go uphill. This is
consistent with a gas eroding the channels.
A different channel morphology is apparent in the lanes not showing fans.
In these regions the channels are dense, more like lace, and are not
radially organized. The third subimage (figure 4) shows an example of "lace."
Observation Geometry
Image PSP_002532_0935 was taken by the High Resolution Imaging Science
Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter
spacecraft on 09-Feb-2007. The complete image is centered at -86.4 degrees
latitude, 99.1 degrees East longitude. The range to the target site was
276.1 km (172.6 miles). At this distance the image scale is 55.2 cm/pixel
(with 2 x 2 binning) so objects ~166 cm across are resolved. The image
shown here has been map-projected to 50 cm/pixel. The image was taken at a
local Mars time of 04:27 PM and the scene is illuminated from the west
with a solar incidence angle of 88 degrees, thus the sun was about 2
degrees above the horizon. At a solar longitude of 181.1 degrees, the
season on Mars is Northern Autumn.
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. The High Resolution Imaging Science Experiment is operated by
the University of Arizona, Tucson, and the instrument was built by Ball
Aerospace and Technology Corp., Boulder, Colo.
