ITC Seminar - Maryame El Moutamid (Cornell)


Monday, November 25, 2019, 12:00pm to 1:00pm


"Evidence of differential rotation inside Saturn from waves of its rings"

The rotation rate of Saturn is not well constrained. This rate has been
estimated based on several investigations of its shape (Anderson and
Schubert 2007, Read et al., 2009 and Helled et al., 2015), its cloud top
winds (Garcia Melendo et al., 2011, Sanchez-Lavega et al., 2014) and its
magnetic field (Ye et al., 2010, Lamy et al., 2011, Andrews et al.,
2012, Provan et al., 2013).  The reason why the interior rotation rate
is not well known is that its magnetic field seems to be closely aligned
with its spin axis. Recent studies have shown that the tilt of the
magnetic field axis is less than 35 arcsecondes with respect to the spin
axis Dougherty et al., 2018), which complicates efforts to ascertain its
rotation rate from periodic signatures in the magnetosphere. Spiral
density waves generated in the rings by mean-motion resonances (MMR)
with Saturn's interior are used here to probe its differential rotation.
  Using a wavelet-based analysis of several occultations of the star
gamma Crucis observed by the Visual and Infrared Mapping Spectrometer
(VIMS) onboard the Cassini spacecraft, we examine dozens weak density
waves in the A, B and C rings.
We argue that these waves are generated by gravity anomalies inside
Saturn, located at different radii from Saturn's center. Our estimates
of Saturn's rotation period fall between 10h 15min 25sec (842.36\dd) and
11h 19min 8sec (763.29\dd). This suggests that the differential rotation
rate of the planet is likely to be around 5%. Estimates of the masses of
these gravity anomalies are around 10^{-11} to $10^{-1
See also: Seminars, 2019 - 20