Martian north polar hazes and surface ice: Results from the Viking Survey/Completion Mission

Abstract

Viking infrared observations of the Martian north polar regions taken during the 1979–1980 Viking Survey/Completion mission have been used to determine the location and nature of the retreating polar cap edge and of an accompanying atmospheric ice haze. The haze is composed of water ice, and its visible opacity is approximately unity, equivalent to 1–2 precipitable microns of water ice. During the polar cap retreat (aerocentric longitude Ls ∼340°–60°), the haze is nearly always present and extends from at most a few degrees south of the polar cap edge to an undetermined distance over the cap interior. The transition from ice‐free ground to a predominantly ice‐covered surface at the cap edge spans 5°–10° of latitude. The ability of the Viking infrared observations to distinguish haze from surface condensate yields a more accurate seasonal regression for the polar cap than can be determined from visual images. Generally, the infrared observations presented here yield a regression similar to those determined from earth‐based and/or spacecraft visual data for the same and for previous northern springs. However, there are differences concerning details of the cap retreat; the thermal data indicate that the Martian seasonal polar cap did extend south of 60°N during this particular late winter and that the midspring resumption of the cap retreat occurs at Ls∼50.