Constraining the Secular Variation of Saturn’s Magnetic Field.

Abstract:

Studying the time dependency of magnetic fields provides valuable insight into planetary interiors as well as general dynamo theory. While the secular variation (time-variation) of Earth’s magnetic field has been observed over decade timescales, the time-variation of other planetary magnetic fields remains relatively constrained. A recent study (Moore et al., 2019) found evidence of secular variation in Jupiter’s magnetic field by comparing 40 years of spacecraft in-situ measurements to a high-resolution reference field model from Juno. Adopting a similar technique, we compare in-situ magnetometer data from previous Saturnian missions to the latest reference field model from the Cassini Grand Finale. Unlike the case at Jupiter, over the almost 40-year span of data analyzed, we find no significant evidence of secular variation in Saturn’s internal magnetic field. The deviations between the data and the model can most likely be explained by external fields alone. This is congruent with the proposed existence of a stably stratified layer on top the deep dynamo, which would axisymmetrize the magnetic field and severely suppress the magnetic secular variation.