Discovery of mass anomalies on Ganymede.

Anderson, John D; Schubert, Gerald; Jacobson, Robert A; Lau, Eunice L; Moore, William B; Palguta, Jennifer L · Science · 2004

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Abstract

We present the discovery of mass anomalies on Ganymede, Jupiter's third and largest Galilean satellite. This discovery is surprising for such a large icy satellite. We used the radio Doppler data generated with the Galileo spacecraft during its second encounter with Ganymede on 6 September 1996 to model the mass anomalies. Two surface mass anomalies, one a positive mass at high latitude and the other a negative mass at low latitude, can explain the data. There are no obvious geological features that can be identified with the anomalies.