On the Spin State of the Asteroid 433 Eros
Abstract
From lightcurve photometry, the asteroid 433 Eros is cigar-shaped (i.e., almost a prolate, biaxial ellipsoid with its short equatorial and polar axes nearly identical. This raises an interesting possibility regarding its unforced spin state. If the two larger moments of inertia are exactly equal, the stable rotation pole direction in body-fixed coordinates is undefined, and perturbations which would normally induce a polar motion analogous to the Earth's Chandler wobble instead will induce a slow constant migration of the body-fixed pole location around the ''waist'' of the ellipsoid. For only a small difference in the two larger moments of inertia, the polar motion follows an ellipsoidal trajectory of axis ratio [ ((C-A)A)/((C-B)B)% right ] (1/2) , and a precession frequency [ ((C-A)(C-B))/(AB)% right ] (1/2) omega , where omega is the axial spin frequency and % A<B< ~ C are the principal moments of inertia. The long axis of the precession ellipse is perpendicular to the long body axis. If the two larger moments of inertia are nearly the same, the precession frequency becomes very long, and the damping time scale somewhat longer than for a highly irregular body. This raises the possibility that Eros may have a small residual polar motion large large enough to be observed by the NEAR spacecraft. Such a wobble would complicate cartography, but at the same time could provide an opportunity to estimate Eros' moments of inertia.
- Publication:
-
AAS/Division of Dynamical Astronomy Meeting
- Pub Date:
- September 1998
- Bibcode:
- 1998DDA....29.1001H