H_2 Quadrupole and H^+_3 Emission from Uranus: The Uranian Thermosphere, Ionosphere, and Aurora

Details H_2 Quadrupole and H^+_3 Emission from Uranus: The Uranian Thermosphere, Ionosphere, and Aurora H_2 Quadrupole and H^+_3 Emission from Uranus: The Uranian Thermosphere, Ionosphere, and Aurora

Oct 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...524.1059t&link_type=abstract

The Astrophysical Journal, Volume 524, Issue 2, pp. 1059-1083.

Astronomy and Astrophysics

Astronomy

19

Infrared: Solar System, Planets And Satellites: Individual (Uranus)

Scientific paper

We present an analysis of the near-infrared emission of Uranus, obtained from 1993 to 1995 at the United Kingdom Infrared Telescope (UKIRT) and the NASA Infrared Telescope Facility (IRTF). We report that in contrast to Jupiter and Saturn, prominent emission in the H_2 quadrupole and H^+_3 overtone and fundamental bands occurs globally. The rotational temperature and luminosity of H_2 and H^+_3 were usually found to vary mildly with longitude. The H_2, and possibly the H^+_3, temperature appears to vary with apparition, indicating a long-term variability of Uranus's thermospheric structure. The thermosphere cooled between 1992 and 1995, while the ionosphere either cooled or otherwise suffered a decline in the column of excited H^+_3. The luminosity in H_2(ν=1) was observed as high as 1.6x10^10 W in 1993 May but remained within 10% of 1.0x10^10 W for four rotational phases observed in 1995 June near solar minimum. The luminosity in H_2(ν=0) is predicted to be 10-20 times higher and less variable. Similarly, the luminosity in H^+_3 was ~1.1x10^11 W in 1995 June, half the value near solar maximum in 1992 April. The declining temperatures and luminosities may be induced by the declining phase of the solar cycle, when the far-ultraviolet/extreme-ultraviolet flux also declines. Although we have observed evidence of auroral emission by both molecular species, auroral processes apparently play only a secondary role in the observed excitation. The observed H_2 emission is consistent with an H_2 population in the ν=1 vibrational state in thermal equilibrium. But H^+_3 appears to deviate significantly from thermal equilibrium in that the ν_2=2 state is underpopulated. The central meridian H_2 intensity distribution is qualitatively consistent with emission from a thick thermosphere. An important result is that the distribution of the H^+_3 fundamental-band emission differs from that of H_2 by having a pronounced concentration toward the subsolar point. We propose that solar extreme-ultraviolet, filtered by Uranus's H corona, is responsible for this concentration and is the dominant source of excited H^+_3 on the planet. The K-band spectrum of Uranus's rings indicates a nearly constant, featureless reflectance over this band.

Affiliated with

Also associated with

No associations

Rating

H_2 Quadrupole and H^+_3 Emission from Uranus: The Uranian Thermosphere, Ionosphere, and Aurora does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with H_2 Quadrupole and H^+_3 Emission from Uranus: The Uranian Thermosphere, Ionosphere, and Aurora, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and H_2 Quadrupole and H^+_3 Emission from Uranus: The Uranian Thermosphere, Ionosphere, and Aurora will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1084047