Sunday, December 22, 2013

Phobos' Shape

Phobos' shape and topography models


Wilner et al


The global shape and the dynamic environment are fundamental properties of a body. Other properties such as volume, bulk density, and models for the dynamic environment can subsequently be computed based on such models. Stereo-photogrammetric methods were applied to derive a global digital terrain model (DTM) with 100 m/pixel resolution using High Resolution Stereo Camera images of the Mars Express mission and Viking Orbiter images. In a subsequent least-squares fit, coefficients of the spherical harmonic function to degree and order 45 are computed. The dynamic models for Phobos were derived from a polyhedron representation of the DTM. The DTM, spherical harmonic function model, and dynamic models, have been refined and represent Phobos' dynamic and geometric topography with much more detail when compared to Shi et al. (2012) and Willner et al. (2010) models, respectively. The volume of Phobos has been re-determined to be in the order of 5741 km3 with an uncertainty of only 0.6% of the total volume. This reduces the bulk density to 1.86±0.013 g/cm3 in comparison to previous results. Assuming a homogeneous mass distribution a forced libration amplitude for Phobos of 1.14° is computed that is in better agreement with observations by Willner et al. (2010) than previous estimates.

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