Near-infrared photometry of the Galilean satellites

Near-infrared lightcurves and phase coefficients at 2.2, 3.8, and 4.8 ωm for the Galilean satellites are presented. The geometric albedo of Io, as determined here, includes emission from volcanoes, especially at 3.8 and 4.8 ωm. No major outbursts were detected during the period of observation 1982–1983, covered by this paper. A broad peak in the 4.8-ωm albedo at longitude ≈270–280° is attributed primarily to volcanoes other than Loki. Results for Europa and Ganymede, showing a trend of decreasing albedo with increasing wavelength, are consistent with icy surfaces for these satellites. For Ganymede, the phase coefficient depends strongly on the wavelength in the near infrared, and has the extremely high value of 0.083 mag/deg at 4.8 ωm. Results for Callisto are consistent with observations of other dark solar system objects at visual wavelengths.