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Voyager disk-integrated photometry of Io

Authors
Journal
Icarus
0019-1035
Publisher
Elsevier
Publication Date
Volume
59
Issue
3
Identifiers
DOI: 10.1016/0019-1035(84)90110-6
Disciplines
  • Mathematics
  • Physics

Abstract

Abstract Voyager full-disk images of Io, available at solar phase angle of α = 2−29° and 101−159°, allow comparisons of the satellite's near-opposition photometric behavior with Earth-based results and the determination of the phase curve out to very high phase angles. The near-opposition data were reduced iteratively for self-consistent phase and rotation curves in each Voyager filter; the resulting phase coefficients, geometric albedos, and rotational lightcurves are consistent with Earth-based findings, except for a previously noted tendency for Voyager to yield somewhat redder spectral information. The derived near-opposition phase coefficients, ranging between 0.016 and 0.024 mag/ deg, decrease with increasing wavelength, a trend weakly noted in some Earth-based observations. The full, α = 2−159° phase curves allow the first direct determination of the phase integral of Io at several wavelengths: q rises from ≈0.7 in the ultraviolet to ≈0.8 in the orange. Combination of the Voyager phase integrals with Earth-based albedo information leads to a best estimate of the bolometric Bond albedo of 0.50 ± 0.10, a value consistent with, but slightly below, previous estimates.

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