Physics
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........11s&link_type=abstract
Thesis (PhD). CORNELL UNIVERSITY, Source DAI-B 65/07, p. 3531, Jan 2005, 238 pages.
Physics
1
Scientific paper
Asteroids are usually modeled as rigid bodies. However, most asteroids are found in a state of principal axis rotation. Because it is highly unlikely that asteroids were formed like that, it is conjectured that internal energy dissipation led to this alignment in a process called “nutational damping”. This indicates non-rigid behavior. Furthermore, contemporary findings suggest that asteroids may not even be coherent bodies. Thus, it is important to incorporate energy dissipation and deformation when investigating the rotational dynamics of asteroids. We first look at “nutational damping” of a symmetric, linear-elastic ellipsoid. The characteristic time for the alignment process is estimated by computing rotational stresses in the body, and neglecting internal gravity and effects of deformation on the dynamics. In contrast with earlier estimates, the elasticity calculation presented here is complete and does not approximate the stresses. Next, we introduce an alternative approach called volume- averaging, where the deformation is averaged through the body's volume. This technique is useful because of its simplicity and flexibility. We first use this technique to compute the corrections to the free nutational motion of a linear-elastic, symmetric, near-rigid ellipsoid. The results obtained extend previous calculations to arbitrary wobble angles and large flattenings. We then investigate the constraints imposed on the internal structure of an ellipsoidal body by its shape and spin state. Possible equilibrium shapes for ellipsoidal asteroids are characterized for internal structures that include rigid-plastic-cohesionless soils and granular aggregates. In the former case, the results match earlier treatments almost exactly, but are obtained with much less effort. We then consider the dynamics of a rigid-plastic- cohesionless soil asteroid in pure spin using the volume- averaged approach. Physically plausible results are obtained. Besides being a test of the volume-averaged method, this problem may help to investigate phenomena such as the formation of asteroids from debris and the re-grouping of asteroids after a disruptive fly-by. Finally, the volume-averaged method is used to study planetary fly-bys of asteroid's The asteroid is modeled as a rigid-granular material. Results comparable to published numerical simulations are obtained. Investigating planetary fly-bys is important because they too offer an insight into the interior of asteroids.
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