Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p31c1555b&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P31C-1555
Other
[5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [5450] Planetary Sciences: Solid Surface Planets / Orbital And Rotational Dynamics
Scientific paper
The spin pole of Titan is very close to a classic Cassini state, or tidally damped configuration. However, the observed obliquity is larger than would be expected for a body with the moments of inertia inferred from the observed gravity field. This suggests that some agent is acting to excite the motion of the spin pole, and frustrate its approach to a steady state, in which the spin pole and orbit pole of Titan would be co-planar with Saturn’s spin pole. A possible excitation mechanism is climate driven mass transport Titan’s orbit plane lies very nearly in the equator plane of Saturn, and the main influence on the seasonal distribution of insolation comes from slow changes in the orbit of Saturn. Saturn’s current obliquity is 26.7 degrees and its orbital eccentricity is 0.054. The distribution of liquid methane lakes on Titan is notably asymmetric, with many more in the north than in the south. It is also true that the current insolation pattern is rather asymmetric, with higher peak values in the south than in the north. If the changing orbit of Saturn drives the liquid hydrocarbons from south to north and back again on the 45 kyr apsidal precession period, this will also influence the moments of inertia of Titan and thereby excite modes of spin pole precessional motion. The hypothesis we seek to test is that this climate-driven mass transport is adequate to excite the observed departure of Titan’s spin pole orientation from a Cassini state. The proposed mechanism for additional driving of Titan’s spin pole precession differs from the mode of excitation of obliquity variations on Earth and Mars, where the dominant effect is variation in the orientation of the orbit plane. What we envision here is instead a parametric excitation of the spin pole motion. In a damped, forced spin pole state, the changes in polar moment will mainly change the obliquity (angular separation of spin and orbit poles), while dissipation will rotate the spin pole out of the plane formed by the orbit pole and invariable pole. One of the chief challenges in testing this hypothesis is that the mass being transported (both the total mass and its spatial pattern) is only poorly known. As a simple ansatz, we take a ring of fixed mass parallel to the equator, and allow it to move from pole to pole. As is moves, its contribution to the quadrupole moment of Titan will change, with maximum contribution at the equator, and minima at both poles. Presumably the background quadrupole moment of Titan, which is forced by tidal and rotational potentials is essentially constant. The climate forcing makes the total moment somewhat time dependent. From the spatial distribution of filled lake basins, we estimate that the transportable mass is of order 1% of the effective oblateness of Titan. Another unknown is the rate of energy dissipation occurring within Titan, which is required to damp the spin pole into a Cassini state. The expectation for a forced damped oscillator, like this, is that the steady state will depend upon both the excitation and the damping.
Aharonson Oded
Bills Bruce G.
Nimmo Francis
No associations
LandOfFree
Influence of Titan's climate-driven surface mass redistribution on spin pole precession does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Influence of Titan's climate-driven surface mass redistribution on spin pole precession, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Influence of Titan's climate-driven surface mass redistribution on spin pole precession will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1496652