A&A Supplement Series, Vol. 126, November II 1997, 183-195
Received October 3, 1996; accepted February 7, 1997
M. Fulle
- L. Colangeli
-
V. Mennella - A. Rotundi
- E. Bussoletti
Send offprint request: M. Fulle
Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, I-34131 Trieste,
Italy
Osservatorio Astronomico di Capodimonte, Via Moiariello 16,
I-80131 Napoli, Italy
Istituto di Fisica Sperimentale, Istituto Universitario Navale,
Via A. De Gasperi 5, I-80133 Napoli, Italy
We present a probabilistic model of the dust mass, flux and fluence which will
be collected by the ROSETTA probe while orbiting around comet 46P/Wirtanen. The
dust environment of the target comet is simulated according to the most recent
data available in the literature. Best fits of the DIDSY-GIOTTO data collected
during the fly-by of comet 1P/Halley have shown that the probabilistic
properties of dust ejection from the inner coma are crucial
(Fulle et al.
1995). Therefore, we pay particular attention to the dust ejection velocity,
which is assumed to have a wide distribution around the most probable values,
and the dust ejection distribution, which is assumed to have a strong
anisotropy peaked towards the sun. To compute the impact velocity in the probe
reference frame, the rigorous keplerian orbit of each grain is considered
taking into account aberrations due to the probe orbital velocity. We analyse
the dependence of the results on the probe orbit parameters, such as true
anomaly, probe-nucleus distance, orbit node and inclination. Computations are
performed for the six main directions of the probe reference frame and for
different values of the acceptance angle. The only way to collect direct grains
is to point towards the nucleus; the mass collected in this direction is almost
independent of the acceptance angle and of the time evolution of dust loss
rate. A strong dependence of the collected dust mass on node and inclination
is evidenced. By assuming an acceptance angle of 
, the flux of reflected
grains received in the two directions perpendicular to the probe orbit is
higher than that in the nucleus direction, for 42% of randomly oriented probe
orbits. The value increases up to 56% when the acceptance angle in the
directions perpendicular to the probe orbit is increased up to 
. The dust
ejection anisotropy produces a strong dependence of the fluxes on the probe
anomaly. For reflected grains, the fluences show relevant depletions at the
largest masses, due to dust orbital effects, and the collected masses strongly
depend on the acceptance angle and on the time evolution of the dust loss rate.
The total dust fluxes are evaluated by assuming a half sphere field of view
(corresponding to an acceptance angle of 
).
keywords: Comets: general -- Comets: individual: 46P/Wirtanen