The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5 degrees and 148 degrees ). A shallow ice table was uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H(2)O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO(3), aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high-to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.On 4 January 2004 universal time coordinated, the Mars Exploration Rover, Spirit, landed on Mars at 14.5692°S, 175.4729°E, within the crater Gusev, a 160-km-diameter Noachian-age impact crater. Previous orbital remote sensing data have been used to hypothesize that Gusev crater may be partially infilled by ancient lacustrine sediments (1, 2). We acquired high spatial resolution multispectral panoramic images of the landing site and its environs to characterize the morphology, composition, and physical and atmospheric properties of the region. Our primary objective is to relate these characteristics to the origin and evolution of the martian crust, with particular emphasis on the search for evidence of liquid water in this region in the past.Instrumentation and calibration. Panoramic Camera (Pancam) is a digital imaging system consisting of two 1024 pixel by 1024 pixel charge-coupled device (CCD) cameras with a 30-cm stereo separation and 0.27 mrad per pixel resolution, mounted on a mast assembly ϳ1.5 m above the martian surface (3). Each camera has an eightposition filter wheel and is capable of obtaining narrow-band color images of the surface or sky in 11 distinct narrow bands or direct neutral-density filter images of the Sun for opacity determinations at two wavelengths. Because of downlink bandwidth limitations, most images were compressed before downlink with the use of a