Upper limits on Titan's magnetic moment and implications for its interior

Abstract

Measurements from the Cassini spacecraft reveal a largely magnetized ionosphere of Titan whose low‐altitude fields could be from the interior of Titan or from penetrating external fields. We use the Cassini magnetic field measurements obtained during 25 Titan flybys to examine the upper limit of Titan's internal magnetic moment. The radial component of the magnetic field near the Titan surface (from 950 to 1100 km) is used to calculate the permanent dipole moment. The calculated upper limit of the permanent dipole moment is 0.78 nT × RTi3, that is, for the z, y, and x directions (0.46, 0.55, 0.29, respectively) nT × RTi3, with an error of ∼0.5 nT in each component. This value is not significantly different from zero, but it is also a factor of 5 lower than the previous upper limit from Voyager observations. This small (possibly zero) magnetic moment of Titan indicates that the interior of the moon does not support a magnetic dynamo, in agreement with the results of recent gravity study which suggest an incompletely differentiated interior. The induced moment of Titan is examined to test the existence of a subsurface ocean in Titan. The data obtained thus far are not sufficient to provide definitive evidence of the existence and depth of a subsurface ocean. This situation will be improved with the addition of measurements after Saturn's equinox when the external inducing field changes significantly.