HST Observations of Early Spring Dust Storms in the North Polar Region of Mars

P.B. James, M.J. Wolff (Univ. Toledo), S.W. Lee (LASP), R.T. Clancy (Space Science Inst.), J.F. Bell III (Cornell U.), L.J. Martin (Lowell Obs.)

Local dust clouds are fairly common near the edge of the subliming south polar cap of Mars, but previous observations of the corresponding season in the north have not revealed such activity. The most recent cycle of Hubble Space Telescope observations commenced shortly after the spring equinox and revealed interesting dust activity near the edge of the north seasonal cap. This talk will discuss these observations.

The first observations of the current cycle took place on September 15 at areocentric solar longitude, Ls = 11. These images show a reasonably mature storm of dimension approximately 1000 km at the edge of the north cap at approximately 62 deg. latitude and 190 deg. longitude. The storm obscures a portion of the polar frost deposits, and southward of the cap edge the dust curls to the east over the relatively dark Arcadia Planitia region; this suggests an interaction with the westerly winds expected at this season near the edge of the cap. Images of the same region in mid October show an unusual, comma shaped dust feature arcing across the seasonal cap; a similar feature was seen at nearly the same Ls but at a different longitude in the 1993 HST observations. Radiative transfer analyses of the first observation are consistent with dust having an opacity of as much as 1.6; the second feature is more diffuse, with an optical depth of about 0.5.

This research was supported through STScI Grant GO-6741.