37th DPS Meeting, 4-9 September 2005
Session 11 Comets
Oral, Monday, September 5, 2005, 4:20-6:00pm, Law LG19

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[11.02] The changes of the orbital elements and estimation of the initial velocities of stream meteoroids ejected from comets and asteroids.

T.J. Jopek, R. Rudawska, P.A. Dybczynski (OA. AM. University)

The value of the initial velocity of the stream meteoroids from the parent bodies is given by the physics of the outgassing of the cometary nuclei and by modeling the collisions between asteroids. In both cases the outflow speed of the meteoroid particles are small (Whipple 1951, Hughes 1977, 2000, Gustafson 1989, Jones 1995, Ma et al. 2002) and as result, the most meteoroid streams have similar orbits to either comets or asteroids. The formulae relating the changes of the orbital elements due to the small increment of the velocity were developed, among others by Plavec (1955), Pecina and Simek(1997), Williams (1996, 2001), Ma et al. (2001), Ma and Williams (2002). Assuming that the members of the observed meteor stream evolved dynamically under the influence of gravitational perturbations only, Pittich (1988), Harris and Hughes (1995), Williams (1996, 2001) estimated the initial velocity of the stream meteoroids. In their approach, Harris and Hughes have used the dispersion of the semimajor axes of the stream meteoroids. Williams proposed the method were used the mean orbit of the stream and the orbit of the identified parent body of the stream. The obtained results are not free from the discrepancy, explained partly by the particular orbital structure of the stream. However Kresak (1992) has strongly criticized the attempts to determine the initial velocities of the stream using the statistics of the meteor orbits. He argued that this is essentially impossible, because the dispersion of the initial velocities are masked by much larger measuring errors and also by the accumulated effects of planetary perturbations. In our paper, we decided to verify the reliability of the methods proposed by Harris and Hughes (1995), and by Williams (1996,2001). We made an numerical experiment consisting of the simulation of formation of several meteor streams and their dynamical evolution over 5000 years. We ejected meteoroids particles from the comets: Halley, Swift-Tuttle, Tempel-Tuttle. During the integration, the initial velocities of the stream members were estimated using the methods proposed by Hughes and Harris, and that by Williams. The results which we calculated till present, shows that the velocities obtained by the Williams method are to high when compared with the known velocities of the stream formation. On the other hand, the velocities obtained using Harris and Hughes method are to small. This work was supported by the KBN Project 2-P03-D-007-22.

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