VLA mapping of 1.35 cm water emission from the Mars atmospheric limb

We report preliminary results of 1.35 cm spectral line observations, in which we employed the NRAO Very Large Array (VLA) interferometer to map the horizontal and vertical distributions of water vapor around the Mars atmospheric limb in early Dec. of 1990. The increased atmospheric pathlengths presented near the limb of Mars and the high angular resolution afforded by the VLA at centimeter wavelengths lead to a remarkably sensitive, remote measurement of water in the atmosphere of Mars. We achieve approximately 300 km horizontal resolution on Mars, operating in the C configuration of the VLA, when Mars was 17.3 inches in diameter. This allows us to resolve the latitudinal and diurnal variations in atmospheric water emission around the limb of Mars. We derive the vertical distribution of atmospheric water from observed pressure broadening in the spectrally resolved lineshapes. These observations, which consist of two eight-hour integrations obtained on Dec. 3-4 and Dec. 6-7, correspond to late winter in the Northern Hemisphere of Mars (L sub s = 344 degrees).