Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.6308l&link_type=abstract
American Astronomical Society, DPS meeting #39, #63.08; Bulletin of the American Astronomical Society, Vol. 39, p.544
Astronomy and Astrophysics
Astronomy
Scientific paper
Correlation of features in overlaps of Cassini RADAR swaths allows determination of Titan's rotational pole position and spin rate (Stiles et al., Persi del Marmo., this meeting). The initial analysis of these data shows Titan to be rotationally variable and to have an internal water ocean.
First, astrodynamical theory predicts that if Titan is in a dynamically relaxed Cassini state there is a relationship between the moment of inertia factor C/MR^2 and the obliquity of a few tenths of a degree. Our results (from two independent analyses of the overlaps) show an appreciable deviation from the expected range of states: possible interpretations are a recent dynamical excitation, or that the theory does not hold because the surface is decoupled from the deep interior.
Second, much as the Earth's Length-of-Day changes by 1ms over a year, seasonal changes in Titan's atmospheric angular momentum (Tokano and Neubauer, 2005) will manifest themselves in a change in surface rotation rate. The change in rate is 10x higher, amounting to some hundreds of seconds, when the surface is decoupled from the interior by a water-ammonia ocean. Our preliminary rotation solutions indicate a present-day spin rate offset of several tenths of a degree per year that may be accelerating. The spin rate and its rate of change suggest that significant atmospheric changes are occurring and that Titan has an internal ocean. The spin state is expected to show further changes in coming years : our preliminary solution has slight differences in the amplitude and phase of the spin variation which may be used to refine global circulation models.
Allison Michael David
Kirk Randolph L.
Lorenz Ralph
Lunine Jonathan I.
Persi del Marmo Paolo
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