Estimating Titan's Spin State from Cassini SAR Data

Details Estimating Titan's Spin State from Cassini SAR Data Estimating Titan's Spin State from Cassini SAR Data

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.6307s&link_type=abstract

American Astronomical Society, DPS meeting #39, #63.07; Bulletin of the American Astronomical Society, Vol. 39, p.544

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Scientific paper

For some 19 areas of Titan's surface, the Cassini RADAR instrument has obtained SAR images during two different flybys. The time interval between flybys varies from a couple months to 2 years. We have used the apparent misregistration (by 10-30 km) of features between separate flybys to construct a refined model of Titan's spin state, estimating six parameters: pole right ascension and declination, spin rate, and these quantities' first time derivatives. Because we have only observed Titan for 2-3 years, our dataset is unlikely to be sensitive to higher order derivatives. We have studied the uncertainty and degree of correlation of the model parameters, and have also searched the parameter space to eliminate the possibility of more than one solution.
Our model spin state differs significantly from both the zero-obliquity synchronous model assumed prior to radar observations and from any other plausible Cassini state. The previously assumed pole location and spin rate certainly cannot account for our data. Because our imaging resolution is between 300 m and 1 km, we are very sensitive to the pole location and spin rate. Our estimated corrections to the pole and spin rate exceed their corresponding standard errors by factors of 40 and 4, respectively. We examined 150 different features in 19 different twice-observed regions. Applying our pole correction reduces the feature misregistration from tens of km to 3-4 km. Applying the spin rate and derivative corrections further reduces the misregistration to 1-2 km. The improved estimate of Titan's spin state is important for multi-disciplinary Titan research, for co-registering data sets from different instruments, and for future Titan mission planning. It also has important implications for Titan's internal structure.

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