The 1994–1995 apparition of Mars observed from Pic-du-Midi

Abstract

The 1995 apparition of Mars was monitored with the Pic-du-Midi 1-m telescope from October 1994 to March 1995. Several thousand images were acquired with a CCD camera through various filters ranging from 0.4 to 1.05 μm . These images complete HST observations of the same apparition with a spatial resolution reduced by a factor of ∼4, but with a better time resolution. Low-resolution spectra were also acquired through a set of interferential filters at opposition, providing indications of mineralogical composition of surface materials. The only significant surface variations during the period are observed in the Cerberus area, which brightened at the end of winter. The whole apparition was very cloudy. The north Polar Hood dissipated in early December ( L s∼25°). Migration of polar clouds to the equator is observed between January 31 and February 6 ( L s∼50–55°). Then an Encircling Cloud Belt obscured most of the surface from February 22 to 24 at least ( L s∼62°). The north polar cap regression is similar to that observed by Mariner 9, although several internal rifts developed during early spring, in particular the dark Lowell band and Rima Tenuis. A standstill is observed in the polar cap regression curve from L s=55 to 70° at latitude ∼70°, at least in the 135–300° longitude range. The very strong spectral feature at 0.95 μm reported from HST observations of Olympia Planitia in July 1995 is not observed in the Pic-du-Midi images. The intermediate-dark region of Propontis I exhibits ferric absorption features consistent with high concentrations of crystalline hematite or other dark ferric materials.