Temperatures and Altitudes of Jupiter's Ultraviolet Aurora Inferred from GHRS Observations with theHubble Space Telescope

✍ Scribed by Y.H. Kim; J.L. Fox; John J. Caldwell

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 513 KB
• Volume: 128
• Category: Article
• ISSN: 0019-1035
• DOI: 10.1006/icar.1997.5699

✦ Synopsis

temperatures derived are in the range 400-850 K with a possible tendency toward lower temperatures for higher methane col-We observed the jovian UV auroral regions with the Goddard umn densities. This tendency and the uncertainty in the temperhigh resolution spectrograph (GHRS) on board the Hubble atures derived may indicate that the temperatures increases Space Telescope (HST) on Apr. 29, May 2, and June 10, 1995. rapidly with altitude around the methane homopause in the Observations of target areas were made in pairs in the two auroral regions. © 1997 Academic Press wavelength ranges 1257-1293 A ˚and 1587-1621 A ˚. Spectra in the long wavelength range are dominated by emissions of the H 2 Lyman band system and show well separated rotational 1. INTRODUCTION features, which we have used to determine the temperatures of the auroral emission regions. Spectra in the short wavelength After the Sun, the jovian aurora is the most powerful range are mostly due to emission in the H 2 Lyman and Werner source of ultraviolet radiation in the Solar System. The total band systems, but their intensities are reduced by hydrocarbon hemispheric power input associated with the UV emissions absorption. The brightest spectral pair was observed toward an area with longitude 155؇ and jovicentric latitude 58؇ when is estimated from the Voyager data to be about 10 14 W the central meridian longitudes (CMLs) were 191؇ and 203؇. (Broadfoot et al. 1979), which is about 10 3 times stronger This area was found to be bright in our previous HST observathan the average terrestrial aurora. This large energy input tions in 1993 and in HST faint object camera images. Assuming causes heating and ionization in the thermosphere and ionothat electron impact excitation is the major source of the jovian sphere in the polar regions, and may have an effect on the aurora, we estimate total emission rates in the Lyman band non-auroral atmosphere as well. Observations of the UV system of about 270 and 46 kR for the long and short wavelength aurora, since its discovery, were made regularly by the Interspectra of the pair, respectively. The attenuation of emission national Ultraviolet Explorer (IUE) over the past two derate in the short wavelength spectrum implies a methane colcades and have provided low-resolution information on umn density of about 3 ؋ 10 16 cm ؊2 , and a temperature of about both its morphology and its spectral characteristics (Skinner 450 K is inferred from the long wavelength spectrum of ; brightest pair. For all six pairs of observed spectra, we estimate Livengood et al. 1990). Recent observations with the HST methane column densities in the range (1-7) ؋ 10 16 cm ؊2 , which, when compared to a standard mid-latitude model, corresponds have provided high resolution images and spectra of the Jovto a pressure range from a few bar to a few tens of bar. The ian UV auroral regions. UV images from the faint object camera (FOC) on board the HST show narrow auroral ovals around both of Jupiter's poles and bright emission near a 1 Based on observations with the NASA/ESA Hubble Space Telescope System III longitude of 150Њ (Caldwell et al. 1992 and unpubobtained at the Space Telescope Science Institute, which is operated by lished; Ge ´rard et al. 1993).