A Second Look at 1975 Observations of the Martian North Polar Region Before the Vernal Equinox

Details A Second Look at 1975 Observations of the Martian North Polar Region Before the Vernal Equinox A Second Look at 1975 Observations of the Martian North Polar Region Before the Vernal Equinox

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0212i&link_type=abstract

American Astronomical Society, DPS meeting #28, #02.12; Bulletin of the American Astronomical Society, Vol. 28, p.1060

Astronomy and Astrophysics

Astronomy

Scientific paper

Calculations using models of the deposition of CO_2 frost on the winter polar surface have predicted a northern frost extending to 50(deg) N latitude or so before vernal equinox (Ls=0(deg) ) . Analyses of Viking visual and IRTM data also show a north polar cap extending to roughly 55(deg) N before vernal equinox. However, in our observations taken at the Hida Observatory in 1975, red filter photographs taken in the period from Ls=340(deg) - 0(deg) revealed dark surface features at the northern high latitudes and did not show bright north polar caps as did those after vernal equinox, at a time when blue filter photographs showed the extensive polar hood. In our analyses of the CCD observations of Mars taken with the Hubble Space Telescope during 1990-1991 and of our CCD observations at the Catalina Station, Steward Observatory, in 1992 and 1994, red filter images taken before vernal equinox also revealed dark surface features in the northern high latitudes (about 64(deg) N). In order to investigate the north polar cap before vernal equinox more fully, we reexamined the data obtained at the Hida Observatory in 1975 with a new image processing system. Red filter images taken at Ls=352(deg) in 1975 revealed dark surface features at northern high latitudes, when blue filter images show the extensive polar hood. The latitude of northernmost dark features observed was 67(deg) N. Similar to our observations in 1992 and 1994, a wide spread north polar cap, which was predicted by most of the existing models and Viking observations was not found in the reanalysis of the observations taken at the Hida Observatory in 1975.

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