Elsevier

Icarus

Volume 17, Issue 1, August 1972, Pages 209-215
Icarus

Io's triaxial figure

https://doi.org/10.1016/0019-1035(72)90057-7Get rights and content

Abstract

Timings from photoelectric observations of four immersions and two emersions of the recent occulation of Beta Scorpii C by Io have made it possible to derive Io's apparent equatorial radius to an accuracy of 2 km, an improvement of nearly two orders of magnitude over previous results. However, when we consider the distortion of Io attributable to rotation and tides raised by Jupiter, the derived mean radius becomes several kilometers less than the observed equatorial radius. If Io were a homogeneous fluid body in hydrostatic equilibrium and in synchronous rotation, which we consider to be reasonable assumptions, it would show a bulge along a line to Jupiter about 20 km in radius greater than the polar radius. The mean radius thus derived is (1818 ± 5) km and mean density (2.88 ± 0.34)g/cm3, the largest uncertainty being attributable to the value of Io's mass. This timing residual of one immersion suggests the existence of a surface irregularity about 3 km below the mean limb of Io. The new value for Io's radius is higher than those previously determined and suggests about 30% lower values for mean densities of all Galilean satellites.

References (5)

  • A. Dollfus

    Diamètres des Planetes et Satellites

    A. Dollfus

    Diamètres des Planetes et Satellites

    Surfaces and Interiors of Planets and Satellites

    (1970)
  • D.L. Harris

    Photometry and colorimetry of planets and satellites

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  • FIRE - Flyby of Io with Repeat Encounters: A conceptual design for a New Frontiers mission to Io

    2017, Advances in Space Research
    Citation Excerpt :

    Dark materials on the surface, seen in paterae floors, are interpreted to be magnesium silicate lavas (Geissler et al., 1999), though silicates or mafic materials have not been spectroscopically identified on Io. Io’s bulk density and topography does suggest that the underlying materials are silicates (e.g., O’Leary and Flandern, 1972; Clow and Carr, 1980) and there has been speculation that the very high temperature lavas (up to 1700 K) are due to ultramafic magma compositions (e.g., McEwen et al., 1998; Keszthelyi et al., 2007), similar to komatiitic volcanism on the ancient Earth (Williams et al., 2000). Imaging and monitoring of eruption temperatures by FIRE would address questions regarding lava compositions.

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Much of this work was done while Dr. O'Leary was Visiting Associate in Planetary Sciences at the California Institute of Technology and Jet Propulsion Laboratory, Pasadena, California.

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