This region of Mars in this image from the High Resolution Imaging Science
Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter receives
very little sunlight in the southern Mars winter, when this was taken. The
bluish areas consist of frost. At the latitude of this image, frost is most likely
composed of water because the temperature is not low enough for carbon
dioxide condensation. The reddish regions are locations where frost has been
removed, most likely by sublimation. The dark, unfrosted regions (for example,
in the channel of the gully on the far right) represent the most recent activity in
the gullies and are possibly a result of seasonal melting.
Besides acquiring monochromatic images of 6-kilometer (3.7-mile) swath
width and variable length, HiRISE can also image the central 20 percent
of the swath width in color. Color images can help resolve ambiguities in
image interpretation and will enable researchers to place compositional
data from other experiments into more specific geologic context. HiRISE
can "see" color in the visible range (the red, green, and blue portions
of the spectrum) and beyond (in the near infrared), thus allowing for the
detection of -- among other features -- characteristic alteration minerals
that require water to form.
Image TRA_000878_1410 was taken by the HiRISE camera on the Mars
Reconnaissance Orbiter spacecraft on Oct. 3, 2006. The complete image is
centered at minus 38.9 degrees latitude, 223.7 degrees east longitude. The
range to the target site was 254 kilometers (159 miles). At this distance
the image scale is 51 centimeters (20 inches) per pixel (with 2 x 2
binning) so objects about 153 centimeters (60 inches) across are resolved.
The image shown here has been map-projected to 50 centimeters (19.7
inches) per pixel and north is up. The image was taken at a local Mars
time of 3:38 p.m. and the scene is illuminated from the west with a solar
incidence angle of 79.9 degrees, thus the sun was about 10.1 degrees above
the horizon. At a solar longitude of 115.5 degrees, the season on Mars is
northern summer.
The full-resolution TIFF file (HiRISE number TRA_000878_1410) can be viewed
or downloaded here PIA01920-hi-res.tif; the full-resolution JPEG can be
viewed or downloaded here PIA01920-hi-res.jpg. [Photojournal note: due to the large
sizes of the high-resolution TIFF and JPEG files, some systems may experience
extremely slow downlink time while viewing or downloading these images; some
systems may be incapable of handling the download entirely.]
