[X] My Assistant

[ngunn]

http://saturn.jpl.nasa.gov/files/20100427_CHARM_Sotin.pdf

[ngunn]

According to this presentation the evidence for non-synchronous rotation has now gone away. How does that square with the SAR image mis-ties of tens of kilometres reported earlier?

[Jason W Barnes]

According to this presentation the evidence for non-synchronous rotation has now gone away. How does that square with the SAR image mis-ties of tens of kilometres reported earlier?

The 10s of km misregistration is due to the pole being offset from the orbit pole -- i.e. a 0.3 degree obliquity for Titan. That's still there, and accounts for the vast majority of the offset. The simultaneous spin-up and precession that nearly cancelled to explain the remaining ~1km offsets is what is apparently gone. I never bought into that in the first place

- Jason

[rlorenz]

Right, in the initial solution, most of the misregistration was accounted for by the obliquity. The best solutions
also required nonsynchroneity, although the correlation in solution space between dRA/dt of the pole (i.e. precession)
and delta-omega (nonsynroneity) was high.

When Bryan Stiles developed these solutions (published in AJ), I had to tell the nonsynchronous/wind/ocean
story (in Science) - if I didnt interpret the nonynch that way, someone else would have....

With new data, and a bug fixed in the fitting code, the solutions have a lower (but still non-zero) delta-omega.
An independent solution by the Italian group now (once an East-West snafu in longitudes of tiepoints was
resolved) gets the same answer.

The obliquity remains (and itself points to a liquid interior).

(Jason was evidently right to be wary of the dRA/dt correlation; we made the best interpretation of what we had
at the time - all anyone can do in a competitive environment. And even if wrong [as a lot of stuff in Science and Nature
turns out to be] the paper stimulated a lot of work on GCMs, gravitational and pressure coupling between core and
crust, etc...... it's been rather fun to watch :-) The dRA/dt, incidentally, is interestingly high.... but
that's another story)

The 10s of km misregistration is due to the pole being offset from the orbit pole -- i.e. a 0.3 degree obliquity for Titan. That's still there, and accounts for the vast majority of the offset. The simultaneous spin-up and precession that nearly cancelled to explain the remaining ~1km offsets is what is apparently gone. I never bought into that in the first place

[ngunn]

The dRA/dt, incidentally, is interestingly high.... but
that's another story)

Does this suggest that the precession, and maybe even the obliquity itself, are not shared by Titan's deep interior but are rather properties of the floating crust alone? It's a fascinating subject: thinking about it raises so many complex questions and possibilities it's hardly surprising if initial interpretations require reappraisal as the story unfolds. Another great reason for staying here a further seven years.