Mercury Science |
Mercury Science |
Nov 16 2005, 02:28 PM
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
Astrophysics, abstract
astro-ph/0511419 From: Stan Peale [view email] Date: Mon, 14 Nov 2005 22:21:56 GMT (314kb) The proximity of Mercury's spin to Cassini state 1 Authors: S. J. Peale Comments: 23 pages,12 figures, In press in Icarus In determining Mercury's core structure from its rotational properties, the value of the normalized moment of inertia, $C/MR^2$, from the location of Cassini 1 is crucial. If Mercury's spin axis occupies Cassini state 1, its position defines the location of the state. The spin might be displaced from the Cassini state if the spin is unable to follow the changes in the state position induced by the variations in the orbital parameters and the geometry of the solar system. The spin axis is expected to follow the Cassini state for orbit variations with time scales long compared to the 1000 year precession period of the spin about the Cassini state because the solid angle swept out by the spin axis as it precesses is an adiabatic invariant. Short period variations in the orbital elements of small amplitude should cause displacements that are commensurate with the amplitudes of the short period terms. By following simultaneously the spin position and the Cassini state position during long time scale orbital variations over past 3 million years (Quinn {\it et al.}, 1991) and short time scale variations from JPL Ephemeris DE 408 (Standish, 2005) we show that the spin axis will remain within one arcsec of the Cassini state after it is brought there by dissipative torques. We thus expect Mercury's spin to occupy Cassini state 1 well within the uncertainties for both radar and spacecraft measurements, with correspondingly tight constraints on $C/MR^2$. http://arxiv.org/abs/astro-ph/0511419 -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Feb 2 2011, 08:26 PM
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Member Group: Members Posts: 903 Joined: 30-January 05 Member No.: 162 |
As always, the folks with the math gene are very much appreciated!
Interesting orbit, compare to Phaeton that we were discussing on the Hyabusa thread. Bruce Murray had a nice scaled drawing of the Mariner 10 176 day orbit in his book Journey Into Space, and also a veritable treasure trove of insider information on the amazing Mariner 10 mission. Bruce met Beppe Columbo! That's how they all found out about the resonant orbit they had accidentally set up. Murray had tremendous respect for Beppe. So too his colleagues setting up their own Mercury mission to be named after him. |
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