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 gas-dynamic shock wave can be seen in a series of images taken with the high resolution camera (HRI) immediately after the impact. Initially, the gas-dynamic shock follows the limit of a strong explosion R t2/5 expanding into a half-space, 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 pre-impact coma in the vicinity of the impact as a spherically-symmetric 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 re-condensation processes during the rapid expansion. Within homogeneous nucleation theory a two-stage 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.
AAS/Division for Planetary Sciences Meeting Abstracts #37
- Pub Date:
- December 2005