The Phoenix mission is inspired by recent findings of subsurface ice by Mars Odyssey. Elements of Phoenix are derived from the Viking landers, Mars Pathfinder, MPL, and the M’01 Lander missions. Phoenix will rely on MGS, Odyssey and MRO data for site selection and context.

Viking: Phoenix will advance many of the original Viking objectives. The Vikings landed at 22° and 48° N. latitude and could only dig 10 cm. Viking 1 landed at a too-dry location to find life. Viking 2 was arguably at a good location to search for life, but did not dig deeply enough to strike ice and possibly organic molecules. Phoenix will extend the Viking mass spectroscopic measurements of atmospheric species by heating soil and ice samples to drive off adsorbed or chemically bonded gases and comparing their isotopic ratios. Phoenix has the potential of finding organic molecules missed by Viking both because the mass spectrometer is more sensitive and because we will examine icy soil. Phoenix will use 30 years of scientific and technological progress to achieve many of the goals of Viking at a much lower cost.

Mars Pathfinder: Pathfinder's primary science goals were related to studying the history of water as reflected in the geology of the local rocks and soils. Phoenix builds on these goals and extends them considerably. Phoenix will use an improved version of the Pathfinder IMP camera to study geomorphology and mineralogy, and to measure airborne dust properties. The Pathfinder MET package followed the seasonal variation of atmospheric pressure, measured the temperature fluctuations of the turbulent eddies near the surface, and detected dust devils. Phoenix will use similar instruments and will extend its focus to determination of the flux of water vapor to and from the surface.

Mars Polar Lander (MPL) and Mars Surveyor Program 2001 Lander (M’01): The failure of MPL left its science goals unaccomplished. The main science goals of the Mars Volatiles and Climate Surveyor (MVACS) payload of MPL were to characterize the surface environment, weather and geology of the southern Polar Layered Terrain. By digging and analyzing samples it could meet additional goals: search for near-surface ground ice; determine the quantity of adsorbed CO₂ and H₂O in Mars soil; quantify subsurface, surface and atmospheric water; determine the abundance of volatile-bearing minerals in the soil that may indicate the presence of past liquid water; and search for climate records in the form of fine-scale layering in near surface materials. Phoenix will use two instruments from MPL (SSI and TEGA) and recover many of the still-valuable MPL science goals.

Phoenix will use the M’01 Lander after extensive modifications to improve the robustness and safety of entry, descent and landing. Phoenix will recover some of the M’01 capabilities with three delivered M’01 instruments (see MARDI, RA/RAC, and MECA in next section). These three instruments are now in bonded stores awaiting the Phoenix mission.

Mars Odyssey: Phoenix will provide important ground truth for Odyssey. The appearance and composition of the sub-surface layers will aid the scientific community in understanding the global variation and structure of subsurface ice. Phoenix will bring a neutron spectrometer to the surface to check the Odyssey ice results on a local scale. Measurements of the thermal conductivity of the dry regolith will calibrate global models.

Future Mars Exploration Program (MEP) missions: Phoenix objectives are unique: no missions are planned to land and analyze the polar near-surface ice reservoir. The Mars Exploration Rovers (MER) are investigating geological processes at sites with no ground ice.

Phoenix brings value to the MEP not only in its science goals, but also by following up the successful Odyssey mission and leveraging capabilities developed for MPL and M’01. A successful Phoenix mission will provide the Mars community with a soft-landing spacecraft for future missions.