36th DPS Meeting, 8-12 November 2004
Session 7 Rings
Oral, Monday, November 8, 2004, 3:30-6:00pm, Lewis

## [7.11] Groundbased near-IR spectroscopy of Jupiter's main ring

M.H. Wong, I. de Pater (UC Berkeley), H.G. Roe (Caltech), M.R. Showalter (Stanford University)

We present near infrared spectrally- and spatially-resolved observations of Jupiter's ring, taken during the Jupiter ring plane crossing in December 2002. The data were acquired using NIRSPEC at Keck.

Our images extend in the spatial direction from the cloud tops (1 RJ) to about 2 RJ, and span the spectral range of \lambda = 2.2 to 3.65 micron. Spectral coverage longward of 2.5 micron is intermittent due to increased terrestrial atmospheric opacity. Spectral coverage to 1.2 micron has been extended via photometric images of the ring at 1.2 and 1.6 micron.

At the time of the observations, the ring opening angle was 1.86\circ and the phase angle was 2.34\circ. We find that the color of the ring is blue'' in K-band: I/F drops off with increasing wavelength.

We detect an absorption band spanning 2.2 to 2.3 micron, which may be due to a calcium-rich clinopyroxene component in the ring material, since the band center matches laboratory spectra of type B clinopyroxenes (Schade et al.\ 2004, Icarus 168:80). There is no robust detection of this feature in the forward-scattered Galileo NIMS spectra (McMuldroch et al.\ 2000, Icarus 146:1; Brooks et al.\ 2004, Icarus 170:35), perhaps because backscattered light is sensitive to larger particle sizes than forward-scattered light. A pyroxene component in the ring material may also provide the absorption needed to resolve the discrepancy near 1 micron between backscattered ring photometry and the model of Throop et al.\ (2004, Icarus in press).

Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.