Formation of Frost Layer of Water Ice on Mars

Formation of the frost layer on Mars' surface in the pictures taken by the Viking 2 Lander is discussed on the basis of the observation of hoar crystals on the snow surface at the Dome Fuji station in the inland area of the Antarctic Ice Sheet on the Earth. The growth rate of a hoar crystal by condensation of water vapor was estimated from the experimental results on artificial production of ice crystals in a cold box and the equation on whisker growth as 10 −5 cm s −1 at 210 K at the Viking 2 Lander site. If this estimation can be extended to the Mars North Ice Cap region at 180 K, the total mass of hoar crystals formed during 100 Mars days in winter can be estimated to be 0.1–1 mm water cm −2. Since these values are of the same order as annual evaporation rates calculated by the modeling, it can be concluded that direct condensation of water ice on the surface will contribute to accumulation at the Mars North Ice Cap.