To simulate the Deep Impact event, we expanded the capabilities of the GEM code (Beer et al. 2006) to assess the lifetime of a size distribution of icy grains released into the coma. We find that grains with 95-99 percent water ice mixed with 5-1 percent refractory material (pyroxene or olivine) fit the observed brightness and color evolution at UV (Schulz et al. 2006) and visible (Walker, MIRA, private communication) wavelengths. The GEM (Grain Evolution Model) predicts the evolution of icy grains from the moment they are ejected from the nucleus until total sublimation. The first step in the code is to calculate the radiative equilibrium grain temperatures using the Mie scattering theory. The second step is to calculate the size distribution of the icy grains ejected from the nucleus by water ice sublimation from the nucleus. The third step is to calculate the sublimation rate, so we can follow the entire distribution out into the coma. The forth step is to calculate the dynamics acting on each and every grain at any time through its sublimation evolution, assuming that the forces acting on a grain are the gas drag force, the radiative pressure force from the Sun, and the nuclear gravitational force. The net result is the ability to map the grains in terms of temperature, lifetime, velocity, amount and to calculate the brightness of the grains’ scattering through their entire evolution or at specific cross sections of time, at any wavelength and for any mixture of ice and “dirt” (e.g., an absorbent material such as pyroxene, olivine, amorphous carbon, tholin, etc.). So far, from an ongoing study to simulate the Deep Impact mission it seems that in order to exhibit the same brightness showed in the Deep impact mission grains of a purer nature are needed.
AAS/Division for Planetary Sciences Meeting Abstracts #38
- Pub Date:
- December 2006