Long Period Variations in Jupiter's Obliquity and Galilean Satellite Inclinations: Influence on Tidal Stress and Dissipation <p> HR: <span class="hr"> 1330h<br></span> AN: <span class="an"> P12A-1056 <a href="../absbook/fm03-P12A.pdf">[PDF]</a><br></span> TI: <span class="ti"> Long Period Variations in Jupiter's Obliquity and Galilean Satellite Inclinations: Influence on Tidal Stress and Dissipation <br></span> AU: <span class="au"> * Bills, B G<br></span> EM: <span class="em"> Bruce.G.Bills@nasa.gov<br></span> AF: <span class="af"> NASA Goddard Space Flight Center, Laboratory for Terrestrial Physics, Greenbelt, MD 20771 United States<br></span> AU: <span class="au"> Ray, R D<br></span> EM: <span class="em"> Richard.D.Ray@nasa.gov<br></span> AF: <span class="af"> NASA Goddard Space Flight Center, Laboratory for Terrestrial Physics, Greenbelt, MD 20771 United States<br></span> AB: <span class="ab"> Spatial and temporal patterns of tidal stress and dissipation within the Galilean satellites are important keys to understanding the dynamics of these bodies. Most past studies have emphasized the role of orbital eccentricity in tidal forcing. There is an additional component of tidal forcing due to finite obliquities of these bodies. The present values of satellite orbital inclinations and obliquities are not particularly representative of their respective longer term variations. As a result, the tidal stress and dissipation regimes at present may not provide adequate explanation of the sources of surface features seen on the satellites. On relatively short time scale ($<$ 10$^{4}$ years), the satellite inclinations and obliquities can be approximated by a model which treats the spin pole of Jupiter as inertially fixed. In that case, each satellite orbit plane responds to torques from the oblate figure of Jupiter, mutual interaction with the other satellites, and a weak solar torque. The free oscillation periods of this system are (7.358, 29.63, 139.97, and 547.89) years. The satellite spin pole motions are driven by torques from Jupiter, acting on the oblate figures of the satellites. The spin pole precession periods are (0.66, 5.16, 31.9, and 320) years. In order to understand longer term variations in forced obliquities of the Galilean satellites, and the resulting variations in tidal forcing, we have investigated the response of the system composed of four satellite orbits and the spin of Jupiter to varying solar torques. The solar torque varies as the orbital inclination of Jupiter varies, on time scales of 10$^{5}$-10$^{6}$ years. The dominant source of orbital variation is exchange of angular momentum between the orbits of Jupiter, Saturn, Uranus, and Neptune. In the secular variation model of Laskar [1988] there are 50 Fourier terms representing the orbit pole of Jupiter. The response of each of the objects (Jupiter's spin and satellite orbits) is a weighted sum of normal mode responses, with weights proportional to the forcing amplitude but also determined by proximity of the forcing period to the normal mode period. The free oscillation periods of the 5-body system are (7.365, 29.635, 139.56, 546.16, and 536,500) years. The spin pole precession period of Jupiter, without satellites, would be 980 kyr, but solar torques on the satellite orbits, coupled to Jupiter via its oblateness, shorten that period to 536 kyr. The largest source of uncertainty in this estimate is the polar moment of inertia of Jupiter, which has a 4% uncertainty. One of the larger terms in Laskar's secular orbital model is nearly in resonance with the lowest frequency term in the 5-body system. This allows substantial variations in the obliquity of Jupiter and the satellite orbital inclinations on 10$^{5}$ year time scales. As the satellite orbits evolve under tidal influence, the strength of resonant forcing will vary. <br></span> DE: <span class="de"> 5450 Orbital and rotational dynamics<br></span> DE: <span class="de"> 6218 Jovian satellites<br></span> DE: <span class="de"> 6220 Jupiter<br></span> SC: <span class="sc"> Planetary Sciences [P]<br></span> MN: <span class="mn"> 2003 Fall Meeting<br></span></p></body></html>