The Ultraviolet Reflectivity of Jupiter at 3.5 Angstrom Resolution from Astro-1 and Astro-2

Abstract

The reflectivity of Jupiter in the wavelength band from 1450 to 1850 A at 3.5 A resolution has been determined from measurements of Jovian equatorial spectra obtained by the Hopkins Ultraviolet Telescope, which was flown on the Space Shuttle Columbia during the 1990 December Astro-1 mission and then on the Endeavour during the 1995 March Astro-2 mission. Good model fits to the data were obtained with only three hydrocarbon absorbers and an electron-impacted H2 dayglow source. Small changes (~10%) in the reflectivity at the limit of the mission-to-mission instrument calibrations were observed; these resulted in somewhat different hydrocarbon abundances in 1990 and 1995. We have determined that the abundances of acetylene, ethane, and ethylene were 39 +/- 3 ppb, 3 +/- 1 ppm, and less than 0.4 ppb, respectively, in 1990, and 28 +/- 3 ppb, 3 +/- 1 ppm, and 0.4 +/- 0.2 ppb in 1995. These mixing ratios are consistent with results from recent IUE spectra at lower resolution. The integrated (1450--1850 A) contribution of the H2 dayglow was 800 +/- 400 R in 1990 and less than 400 R in 1995, which was a period spanning solar maximum and solar minimum.