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.