36th DPS Meeting, 8-12 November 2004
Session 21 Comets: Nuclei
Oral, Wednesday, November 10, 2004, 10:30-12:00noon, Clark

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[21.06] Estimating the Nucleus Bulk Density of Comet 81P/Wild 2

B. J. R. Davidsson (ESA/ESTEC), P. J. Gutierrez (Laboratoire d'Astrophysique de Marseille)

During the successful NASA Stardust flyby of Comet 81P/Wild 2 in January 2004, a wealth of information about the object was collected. To further deepen our knowledge about this comet, modeling of its non-gravitational force has been made, in order to estimate the nucleus bulk density.

The nucleus is modeled as a triaxial ellipsoid, covered by active and inactive regions, having the dimensions and spin axis orientation as measured during the flyby. The bulk density is estimated by requiring that a model nucleus simultaneously must reproduce the empirical water production rate (Q\mathrm{H_2O}) and non-gravitational changes in the orbital period and the longitude of perihelion.

For a postulated rotational period of 12 hours, using a spin axis obliquity and argument of 124\circ and 333\circ, respectively [Sekanina et al. 2004, Science vol. 304, pp. 1769], we find a bulk density of at most 360\,\mathrm{kg\,m-3}, although nominal Q\mathrm{H_2O} measurements are poorly reproduced. For the reversed spin axis orientation, a very good Q\mathrm{H_2O} reproduction can be made, resulting in a density of 380-600\,\mathrm{kg\,m-3} (the upper limit increases to 760\,\mathrm{kg\,m-3} if worse Q\mathrm{H_2O}-fits are considered). The dependence of these results on the applied thermophysical model and rotational period is discussed.

This research has been conducted with financial support from the European Space Agency (ESA).

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.