JACK FROST VISITS UTOPIA -- Viking Lander 2, witnessing a gradual retreat of the frigid winter it has survived at its Martian landing site, Utopia Planitia, revealed fret for the first time in pictures taken in September. The frost was first seen in a black-and-white picture and was then imaged in color to produce this picture September 25, 1977. The view is to the rear and over the top of the top of the Lander toward the southeast; camera reference charts and the Lander's large, two-way Earth-communication antenna can be seen. The color difference between the white frost and the typically reddish-brown soil confirmed that the bright patches seen in the earlier black-and-white picture were produced by frost rather than by a change in surface soil features. The frost appears in patches generally associated with shadowed areas -- such as near rocks; the darker rocks in the scene vary in size from about 10 centimeters (4 inches) to 76 centimeters (30 inches). It is hoped that a continuing analysis of the pictures, in correlation with meteorological and Orbiter thermal data, will help Viking scientists to determine if the frost was routinely deposited during the cold nighttime hours -- to disappear each day as the sun caused it to sublimate, or if the frost was condensed as a heavier deposit that took many days to disappear. Nighttime temperatures reached a low of 160 Kelvin (-113 C, -171 F) and rose during the day to 175 Kelvin (-98 C, -144 F). Though extremely cold by Earth reference, such temperatures are too warm for a frost composed only of frozen carbon dioxide (dry ice) which condenses on Mars at a temperature of approximately 151 Kelvin (-122C, -188 F). Preliminary analysis therefore supports the latter of the two possibilities that the frost has a longer than daily term, and strengthens the theory that it is more likely a carbon dioxide clathrate (composed of approximately six parts water to one part carbon dioxide).
