Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1774556 | Icarus | 2009 | 9 Pages |
Abstract
Using TEXES at the IRTF telescope, we obtained high-resolution, mid-infrared, longslit spectra of Jupiter's northern auroral “hot spot” near System III longitude 180° to search for selected pure-rotational and ν1âν2 difference band lines of H3+. Because these lines have not been investigated in the laboratory, we used theoretically predicted frequencies and line intensities to guide this search. No pure rotational H3+ line emission was detected near the predicted frequencies. However, two metastable ν1âν2 difference band lines appear to have been marginally detected at the 68% confidence level (1 â Ï). The non-detection of the pure rotational line sets a 1 âÂ Ï upper limit to the vertical column abundance of H3+ in the northern jovian aurora of 8.4 Ã 1012 cmâ2, which is independent of any assumption concerning the departure of the vibrational H3+ energy level populations from thermal equilibrium. This is consistent with the column 6 Ã 1012 cmâ2 inferred by Melin et al. [Melin, H., Miller, S., Stallard, T., Grodent, D., 2005. Icarus 178, 97-103] from their non-LTE H3+ emission model, in which the fundamental band ro-vib levels are underpopulated by a factor of 6-10 relative to LTE. We find that the IR-inactive ν1 levels of H3+, from which the jovian ν1âν2 difference band emission originates, are populated in thermal equilibrium. The difference band lines thus serve as proxies for the rotational lines in establishing the total auroral H3+ column. As a result, the marginally detected 943.953 cmâ1 ν1âν2 difference band line implies a vertical H3+ column abundance in the range (4.5 ± 3.1) Ã 1012 cmâ2, consistent with the upper limit from the rotational line. The difference band line constrains the vibrational relaxation of the IR-active ν2 fundamental band in Jupiter's aurora to a factor of 4.5-7.5, with an uncertainty ±68%, which supports the model-dependent result of Melin et al.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Space and Planetary Science
Authors
Laurence M. Trafton, Steven Miller, John H. Lacy, Thomas K. Greathouse,