The
2007 Phoenix Mars Scout will land at a site between 65 and
75º N, where Odyssey observed near-surface ground ice. The
specific landing site will meet the following criteria:
High probability for the presence
of ice as determined by GRS data.
Safe
landing within spacecraft design constraints as determined
by detailed examination of MGS Mars Orbital Camera (MOC),
MGS Mars Orbiter Laser Altimeter (MOLA), Odyssey Thermal
Emission Imaging System (THEMIS), and MRO High Resolution
Imaging Science Experiment (HiRISE) images Presence of evaporites
indicating that water has ponded and evaporated, if discovered
by maps created from GRS, THEMIS, and MRO Compact Reconnaissance
Imaging Spectrometer for Mars (CRISM) data .
These
MOLA-based relief maps show a landing error ellipse in the
smooth terrain within the general region thought to abound
with ice. The landing area has low roughness values, indicating
the terrain is smoother than most of the Martian surface.
Geologically
interesting terrain, active polar and periglacial processes. The GRS hydrogen data, converted to weight percent
water ice, show a wide band of high ice abundances within
the latitudes accessible to the Phoenix lander. This provides
a huge number of possibilities for landing sites that meet
the criteria listed above. As an example of a possible landing
site, we focus on analyses of sites within the high water-ice
abundance region centered at approximately 67.5º N and 240º
E. This location clearly meets the first criterion, since
ice abundances are nearly as high as those of the exposed
polar cap. The second criterion, safe landing, is critical
and must be examined carefully using all available data.
The two prime concerns for landing are that slopes be less
than 20º over the length scale of the lander and that there
be only a tiny probability of landing on obstacles taller
than the footpad-to-deck clearance of 37 cm.
The above figure shows a MOLA-based shaded relief
map with a possible landing error ellipse (guided entry
not implemented for worst case) shown in the smooth terrain
within the general region of predicted high abundances of
ice. Analyses of the MOLA-based data indicate that this
general area has low roughness values —approximately 1±0.6
m. This mean roughness within the 150-m MOLA footprints
indicates smooth terrain over this scale, relative to most
of the Martian surface. The smooth terrain is consistent
with analyses that examined 460 MOC images located northward
of 55 N. They found textures interpreted to be due to periglacial
processes, including terrain they describe as having basketball-like,
wrinkled-looking, and polygonally shaped features. Importantly,
they estimate the knob height in the basketball terrain
to be <0.2 m, with separations of ~ 10–20 m. This means
that the slopes are gentle and easily within the slope constraint
listed above. The most likely obstacles to be encountered
are rocks. Thermal inertias computed from TES data show
values of 230±48 J/(m2Kvs)—
a range that indicates slightly indurated soillike material
covers the surface, at least to depths of the diurnal skin
depth of approximately several centimeters. Given the siteaverage
thermal inertia, the likelihood of landing on a high rock
is very small.
The
search for geological terrains for which hypotheses can
be developed and tested using Phoenix data will be tightly
coordinated with the MEP office, through its landing site
selection support. The decision on the final landing site
will be through the NASA Associate Administrator for Space
Sciences. We expect to involve the research community in
helping the PI develop his recommendations, using the successful
approach used by the MER mission. Specifically, working
with the Phoenix team, the landing site office, and the
community, we will host several workshops to solicit input
for candidate landing sites. The team would then help down-select
sites that meet engineering and science requirements so
that the PI can make viable recommendations.