Analytical solution for the expansion of the Deep Impact vapor plume
Abstract
In NASA's Deep Impact mission, the spectacular collision of a 370 kg copper projectile with the comet 9P/Tempel 1 took place at a relative speed of 10.2 km/s. The appearance of a gasdynamic shock wave can be seen in a series of images taken with the high resolution camera (HRI) immediately after the impact. Initially, the gasdynamic shock follows the limit of a strong explosion R t^{2/5} expanding into a halfspace, to a good degree of approximation. Due to stratification of the coma the geometry is different from hemispherical expansion at a later stage. The geometry and dynamics of the shock wave is investigated in Kompaneet's approximation, simplifying the preimpact coma in the vicinity of the impact as a sphericallysymmetric stationary outflow. The solution is used to estimate the fraction of the kinetic energy of the impactor consumed for vaporization. A second part of the investigation is devoted to recondensation processes during the rapid expansion. Within homogeneous nucleation theory a twostage condensation process occurs, forming aerosols at two characteristic sizes. Such a behavior is found in the case of water vapor as well as for evaporated silicates. Both cases can be distinguished by the typical sizes and temperatures of aerosols.
 Publication:

AAS/Division for Planetary Sciences Meeting Abstracts #37
 Pub Date:
 December 2005
 Bibcode:
 2005DPS....37.4415D