Structure of the martian north polar cap and vernal hood system at L s 61‡–66‡ of the 1995 apparition

Abstract

The boundary and internal structure of the north polar deposits and polar hood vernal remnant on Mars have been mapped at L s 61‡–66‡ on the hemisphere centered on longitude Ω = 0‡, using images obtained in Feb–Mar 1995 with the Swedish Vacuum Solar Telescope on La Palma. On red light images, several internal rifts, including the historically well documented Rima Tenuis and Rima Hyperborea, as well as an internal, long absent, annular rift were mapped. The ground cap was asymmetric with a mean boundary at 72‡ N for Ω = 270‡, increasing to 77‡ N at Ω = 90‡. Images in green light showed the locations of high opacity hood clouds, including an extensive outflow to 67‡ N at Ω ≈ 100‡. The state of the cap and hood is compared with the findings of previous studies and the historical significance of the annular rift structure is discussed. It is concluded, based on the structure of the deposited laminae, that the north polar climate was nearly, or possibly slightly milder than, normal at the northern hemisphere spring season studied.