A Four-Year Baseline Estimate of Titan's Spin State from Cassini SAR Data
Abstract
In a previous study, we examined 20 areas of Titan's surface in which SAR images during two different flybys had been obtained over the course of the first 2 years of Cassini's tour of the Saturn system. We used the apparent mislocations (tens of km) of features between separate flybys to construct a model of Titan's spin state, estimating six parameters: pole right ascension and declination, spin rate, and these quantities' first time derivatives. We were only able to estimate first order derivatives because of the short time baseline. This limitation of the previous model prevents it from being applicable over the long term. One obvious example of this shortcoming is that Titan cannot have a perpetually increasing spin rate. Now that we have a longer (4-year) baseline with 40 regions of multi-flyby SAR imagery, we extend the fit beyond the simple first order time varying model in order to predict long term (decadal) variation in Titan’ spin rate and the location of its pole. The longer baseline allows us to observe a change of sign in the derivative of spin rate and estimate the period of the spin rate variation. An improved predictive model of Titan's spin state is useful for co-locating data sets from different instruments, and for future Titan mission planning. It also has important implications for Titan's internal structure.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #41
- Pub Date:
- September 2009
- Bibcode:
- 2009DPS....41.0702S