Mass and interior of Enceladus from Cassini data analysis

Abstract

Gravity results are available from radio Doppler data acquired by the Deep Space Network during the encounter of the Cassini spacecraft with Enceladus in February 2005. We report the mass of Enceladus to be ( 1.0798 ± 0.0016 ) × 10 20 kg , which implies a density of 1608.9 ± 4 kg m −3 . For a core made of hydrated silicates with a density of 2500 kg m −3 the core radius is ∼ 190 km and the quadrupole moment C 22 ∼ 1.4 × 10 −3 . If Enceladus is in hydrostatic equilibrium, the larger than previously anticipated density implies that the recently proposed secondary spin–orbit resonance cannot be present. Therefore, the source of endogenic activity of Enceladus remains unexplained.