Phoenix Mars Lander Update

As the martian winter approaches, foretelling the likely end of NASA's Phoenix mission, the lander is struggling to finish up its extended study of northern martian soil, which includes delivering soil samples to onboard gas analyzers and a wet chemistry lab. At a press conference on Sept. 29, team scientists reported evidence for falling snow, which melted before it hit the ground. They also reported the definite detection of calcium carbonate in the soil, although detection of a silicate-based clay remains ambiguous. Both minerals suggest an interaction with a past watery environment. Paradoxically, probes inserted into the surface show that the soil is extremely dry, even though there's an ice layer a few inches belowground. Scientists continue to puzzle over the finding of perchlorate ions, ClO4^–, which can act as a desiccant (C&EN, Aug. 11, page 13). That might be why the soil is so dry, they said. Although there's been scant evidence for organic compounds, the scientists will continue to look for them as Phoenix finishes its last experiments. The craft's optical microscope also captured an image of magnetically separated multicolored soil grains.