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Fig. 12.17
Rippled (not deeply
eroded, as had been thought from
lower-resolution MOC images)
dunes on the floor of Herschel
crater. HiRISE
PSP_002860_1650. NASA/JPL/
U of A. Inset, portion of browse
image. Documented 1 m
movement in the Herschel dune
field, which occurred between
two HiRISE images taken 1.5
Mars years apart. PIA14879
rate here of only 1-2 cm per Mars year (Fenton 2006a). The
combination of THEMIS infrared and visible data
(Fig.
12.18
) provided interesting insights into the physical
properties of this dune field (themis.asu.edu/feature/7).
Color represents the nighttime temperatures, where blue is
relatively cold and red is warm, corresponding to dusty and
rocky exposures, respectively. The crests of the 150-200 m-
tall dunes are consistently warmer (by *6 C) than the
adjacent troughs between the dunes, suggesting that wind
has swept most of the dust from the crest areas. Also, the
red (rocky) areas are exposed layered material that may
have provided a local source for at least some of the sand-
sized materials.
Richardson crater (72.1 S, 179.5 E). Richardson crater is
55 km in diameter, and is located in the polar region of the
southern cratered highlands. The dunes in this crater have
received considerable attention from multiple spacecraft
camera teams because they show distinctive 'spotted' pat-
terns as the seasonal cap of carbon dioxide frost vaporizes
from the sand surface during southern spring (Fig.
12.19
).
The defrosted 'spots' may expose sand that could then be
blown or avalanched onto adjacent frost-covered areas,
which in turn would enhance the removal of the frost from
these areas.
Nili Patera (8.0 N, 72.0 E). Instead of occurring within
an impact crater, this dune field (CRISM image) is located
within the broad caldera present at the summit of the
shallow-sloped Nili Patera volcano (Fig.
12.20
). The bar-
chan dunes of Nili Patera were the first place to provide
documented evidence of ripple and dune movement on
Mars of at least a meter, using repeat HiRISE images
(Silvestro et al. 2010a). The rippled surfaces of the barchans
and barchanoid ridges in the Nili Patera region have con-
tinued to be monitored with HiRISE as part of the contin-
uing effort to document dune and ripple movement
occurring today across the entire planet (Bridges et al.
2012a), as well as the first place on Mars to apply the
sophisticated COSI-Corr software which was designed to
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