Detection of H2 Quadrupole Emission from Saturn

Details Detection of H2 Quadrupole Emission from Saturn Detection of H2 Quadrupole Emission from Saturn

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.4107t&link_type=abstract

American Astronomical Society, DPS meeting #42, #41.07; Bulletin of the American Astronomical Society, Vol. 42, p.1039

Astronomy and Astrophysics

Astronomy

Scientific paper

We report the first detection of near-IR H2 quadrupole emission from Saturn. Such emission had been previously detected in the near-IR spectra of Jupiter's aurorae, and in the thermosphere and aurorae of Uranus, but the low intensity had prevented detection in Saturn's spectrum. Although H3+ emission has been detected for all three planets, it is similarly the dimmest on Saturn, a fact that may result from Saturn's having the lowest thermospheric temperature with possibly the highest homopause altitude. Unlike for H3+, which is destroyed by hydrocarbons below the homopause, H2 emission is not restricted to arising from above the homopause. Comparison of the H2 emission to the H3+ emission may therefore help to constrain Saturn's homopause altitude, which plays a critical role in characterizing Saturn's thermospheric chemistry and energy balance. Comparison of temperatures may also be diagnostic. Simplistically, a hot H2 temperature would imply hot H3+, and so a lower H3+ column to explain the observed brightness, and hence a higher homopause. Conversely, cool H2 would imply cool H3+, a longer H3+ path, and a lower homopause, as Melin et al (2007; Icarus 186, 234) suggest may be the case.
The observations were done at the IRTF telescope using the CSHELL spectrograph at R=21,500 during Jan 19-20, 2008, when we first detected H2 Q(1) emission in Saturn's southern aurora, and on Jan 8-9, 2009, when we similarly observed three of the four targeted K-band auroral H2 emission lines, S(1), Q(1), and Q(3). Observing time ran out before S(0) could be observed. We present the observations and discuss preliminary results in terms of Saturn's homopause.

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