A team headed by P.B. James (1994) began monitoring Mars in December 1990.
Observations in 1992-3 spanned a range in L
(planetocentric longitude of
the sun measured eastward in the planet's orbital plane from the planet's
vernal equinox) of 258 to 93 degrees. The data set includes 230-320 nm FOS
meridional scans to measure atmospheric dust and ozone. During this time Mars
had been too close to the sun to observe with HST for two periods from May 1991
to May 1992 and June 1993 to August 1994. Observation with the PC mode of
WFPC-1 included Mars when its angular size ranged from 16.5 to 4.8 arcseconds.
Even at the smallest diameter, deconvolved images yielded resolution that was
comparable to good groundbased images.
This analysis followed the development of the polar ice caps and hood and winter cloud banks which showed behavior similar to that expected from the Viking data. At the same time, the data indicated that the 1980's and early '90's have been relatively dust free on Mars. The ability of WFPC-2 to monitor planetary ozone (230 nm) and the possibility of monitoring the planet over several Martian years should provide useful constraints to better understand the planet's climate.