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Gravitational evidence for an undifferentiated Callisto
J D Anderson1, E L Lau, W L Sjogren
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91109-8099, USA. john.d.anderson@jpl.nasa.gov
Nature
|May 15, 1997
Summary
Callisto is likely a homogeneous mix of ice and rock, unlike its differentiated Galilean moons. This undifferentiated state suggests Callisto lacked sufficient internal heat for compositional separation.
Area of Science:
- Planetary Science
- Astronomy
- Geophysics
Background:
- Previous models of Galilean satellite interiors included undifferentiated or layered structures.
- Prior data for Callisto offered limited information, mainly its mean density.
Purpose of the Study:
- To determine the interior structure of Callisto.
- To compare Callisto's internal structure with other Galilean satellites (Io, Europa, Ganymede).
Main Methods:
- Analysis of gravitational field measurements from the Galileo spacecraft.
- Modeling of Callisto's internal composition based on density and gravitational data.
Main Results:
- Callisto appears to be a homogeneous body, not differentiated.
- Its composition is estimated as a solar mixture of 40% ice and 60% rock (including iron and iron sulfide).
- This contrasts with the differentiated interiors of Io and Ganymede.
Conclusions:
- Callisto's undifferentiated state is consistent with a lack of a significant internal heating phase.
- The absence of internal heat prevented the separation of rock and metal from ice.
- This finding provides new insights into the thermal evolution of the outer Galilean moons.
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