Spectro-imaging observations of H3+ on Jupiter

Narrow-band filter, high-spectral-resolution (0.2 cm(-1)) spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope, have provided maps of the emission from the H2 S1(1) quadrupole line and several H3+ lines. H2 and H3+ emissions appear to be morphologically different, especially in the north, where the latter notably exhibits a 'hot spot' near lambdaIII = 150-170 degrees System III longitude. The spectra include a total of 14 H3+ lines, including two hot lines from the 3v2-v2 band, detected on Jupiter for the first time. They can be used to determine H3+ column densities, rotational (Trot) and vibrational (Tvib) temperatures. We find the mean Tvib of the v2 = 3 state to be lower (960 +/- 50 K) than the mean Trot in v2 = 2 (1170 +/- 75 K), indicating an underpopulation of the v2 = 3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from v2 observations. These features can be explained by the combination of both a large positive temperature gradient in the sub-microbar auroral atmosphere and non-local thermal equilibrium effects affecting preferentially hot and combination bands. Spatial variations in line intensities are mostly owing to correlated variations in the H3+ column densities. The thermostatic role played by H3+ at ionospheric levels may provide an explanation. The exception is the northern 'hot spot', which exhibits a Tvib about 250 K higher than other regions.