Martian north polar cap 1979–1980

Abstract

A regression curve for the north polar cap of Mars is extracted from the photographs obtained at Kwasan Observatory and at Hida Observatory during the 1979–1980 apparition. The north polar cap was first observed at L s = 26°, and the latitude of the edge of the cap was about 66°N. The retreat of the cap stopped until Mars reached L s = 57° when the cap started to shrink. The edge reached a latitude around 80°N at L s = 85° and then became almost stationary. The roughly constant dimension of the north polar cap before mid‐spring appears to be a regular phenomenon. But the onset time when the cap starts to shrink after the temporary stop appears to be different from year to year. The measurements of the edge of the permanent cap showed an asymmetric shape in relation to the pole. The cap extends farther to the south for longitudes near 0° than for those near 180°. The shape of the permanent cap for L s = 84°–101° in 1980 agrees very well with that for L s = 97° in 1972 obtained by Mariner 9.