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Astron. Astrophys. 324, 770-777 (1997)

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5. Discussion

We have performed an accurate modelling of dust trajectories starting from cometary emission (Fulle's model) and then following the subsequent orbital evolution integrating the Newton equations. Among SPC we have selected P/GS and P/SW1 which represent two significantly different objects from a dynamical point of view. The orbital evolution of dust particles emitted by these two comets is then well representative of the possible behaviours of cometary dust grains because of the different balancing between P-R drag and Jupiter perturbations.

For P/SW1 grains, Jupiter perturbations force the particles in highly cahotic routes and, as a consequence, memory of the inital conditions are lost on a short timescale as shown by comparing the perihelia distributions of the grain clouds characterized by different ejection configurations. Because P-R drag is not a leading force, the size of the particles is not relevant for the dynamical behaviour. Very few particles produced by P/SW1 reach the inner region of the Solar System and the sink mechanism is not vaporization by the Sun, but ejection from the Solar System or collisions.

For P/GS grains again the Tisserand invariant represents a useful criterion for estimating the relevance of the P-R drag in perturbing the grain orbits. 20µm particles are dominated by P-R drag and rapidly fall into the Sun. Most of the 200µm particles follow the Tisserand invariant as they are kept far from the Sun having a longer lifetime.

We conclude that Jupiter perturbations oppose to the P-R drag forces and reduce significantly the contribution of SPC to the inner zodiacal dust cloud in two ways:

1) preventing particles to spiral towards the Sun

2) increasing the average eccentricity and reducing consequently the mean density of particles in the inner regions.

This implies that the contribution to the zodiacal dust mass supplied from SPC estimated simply adding up the values of the dust productions rates could be overweighted.

A further useful use of the Tisserand invariant could consist in distinguishing the parent sources of meteoroids collected with near Earth space platforms. If accurate measurements of the velocity vectors are performed, the orbital elements of the grains (in particular larger grains) could be associated, through the invariant curve, to the parent cometary source.

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998