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Session 29 - Planets, Asteroids and Comets.
Oral session, Monday, June 08
As we have demonstrated earlier (1997, ApJ 474, 496), the kinetic equation written in the space of orbital coordinates such as semimajor axis a and eccentricity e makes it possible to investigate the gravitational scattering of particles on the planets in a fast and effective way. In the present work, we expand our previous 2-D analysis (inclination i=0) to a much more general 3-D situation when i\not=0 and also include the Poynting-Robertson drag (the latter is based on our method described in 1997, ApJ 488, 268). For a drifting particle (i.e. for its orbital torus), we compute a sample of N gravitationally scattered particles flying by the planet at N distances from the planet's center. The weight of each scattered particle is proportional to the probability of the flyby within the ring whose inner and outer radii are (r, r+dr), respectively. This enables us to derive the scattering angle \phi as a function of r and the particle's velocity V relative to the planet. Actually, for each (a,e,i)-particle of velocity V, we find the distribution in r and therefore the distribution in \phi. By evaluating the sum of such distribution for all drifting particles produced by all available sources of dust, we get the distribution in the net scattering angle. With the knowledge of initial velocity components of particles, we compute the particle's velocity components after scattering and therefore its new (a,e.i).
We illustrate this technique by computing the gravitational scattering for dust particles of both asteroidal and cometary origin. The three main results worth noting are: (i) the gravitational scattering leads to a much thicker shape of the zodiacal cloud compared to the distribution of the flat component of dust sources; (ii) large particles are scattered more efficiently and therefore they would occupy a larger volume than the smaller-size particles; and (iii) the drifting asteroidal dust is scattered in a much more efficient way than the dust of cometary origin, which is explained by smaller (on average) velocities of asteroidal particles.
Program listing for Monday