Denk, T., Roatsch, T., Oberst, J., Neukum, G., Porco, C., Thomas, P., Helfenstein, P., and Squyres, S. (2001). "Himalia -- First Disk-Resolved Observations of an outer Jovian Satellite." European Geophysical Society XXVI General Assembly PS6.01.


Abstract

On Dec. 18, 2000, after the deadline for this abstract, the Cassini spacecraft is scheduled to obtain disk-resolved, ISS narrow-angle camera (NAC) images of J6 Himalia, the largest of the 10 outer jovian satellites. Cassini's flyby distance of 4.44 million km will have been the closest to any known object in the Jovian system, resulting in a spatial NAC resolution of 27 km/pxl. With a diameter of ~170 km (pre-Cassini value from Cruikshank 1977) and a phase angle of 70 deg during the five hours of observation, the expected size of the Himalia disk is ~4x7 NAC pixels.
The plan includes four different ISS NAC observations. Each of the first three sequences will contain 20 images taken through different color filters, the spectral range lies between 0.34 and 1.0 um. The last observation will contain 24 different color filter images at wavelengths between 0.26 and 1.0 um, and nine polarization filter images at three different wavelengths (0.34, 0.56, and 0.73 um). If the pre-Cassini rotation period estimate of ~9.5 hours (Degewij et al. 1980) is correct, about 3/4 of the surface of Himalia will be observable. Using the Himalia NAC data, we plan to determine basic parameters such as size, shape, rotation period, spin-axis orientation, and albedo of this moon. Surface color and color variations as well as possible large-scale brightness differences should also be measurable, as might be possible spectral absorption features which have been proposed from earth-based observations (Jarvis et al. 2000). Initial results will be presented at the conference. References: Cruikshank, D.P. 1977, Icarus 30, 224-230. Degewij, J. et al. 1980, Icarus 44, 520-540. Jarvis, K.S. et al. 2000, Icarus 145, 445-453.