Comet Halley: Nucleus and jets (results of the VEGA mission)

Dust coma morphology in the Deep Impact images of Comet 9P/Tempel 1

“…Even comets that appear featureless at large distances reveal structure as they get close to the Earth, suggesting that, with enough resolution, features could be observed in the coma of any comet. In support of this conjecture, each of the four comets imaged by spacecraft (1P/Halley, 19P/Borrelly, 81P/Wild 2, and 9P/Tempel 1) exhibited numerous well-defined, and even collimated, jets in their inner comae (e.g., Sagdeev et al, 1985;A'Hearn et al, 1986A'Hearn et al, , 2005Sekanina and Larson, 1986;Soderblom et al, 2002;Brownlee et al, 2004), including small-scale features that were not resolved in ground-based observations. The existence of these features in so many different objects suggests that there is a common mantling process (or other process that restricts local activity) that acts to insulate most of the comet's surface from sublimation.…”

P/Halley, the Model Comet, in View of the Imaging Experiment Aboard the Vega Spacecraft

“…The model is shown in Figure 1 from three different directions. When the model was constructed, a non-Lambertian scattering function cos* on cos* -1 a e with k=0.7 was used, based on our earlier measurements (Sagdeev et al, 1985) for the surface scattering. We do not claim uniqueness for this model, though not much freedom has remained after reproducing the visual observations, with the exception of regions around the small end, which is not visible on the images.…”

Numerical modeling of Deep Impact experiment

“…Calculated spatial distributions of density for different comet materials are shown in Figs. 2-4 at 100 ms, 500 ms and 1000 ms,respectively 2. In comparison with previous calculations[6], modeling results of the realistic collision at angle of 30 degrees demonstrated a significant difference in dynamics of impactor, crater size, and amount of ejected matter.…”

“…Among the first successful projects we can list the missions of automatic interplanetary stations Vega-1 and Vega-2 to the Halley comet in 1986 [2]. More than one and a half thousand photographs of the comet from different distances (8-14,000) Â 10 3 km were obtained, the reflectivity of the surface of the cometary nucleus was determined, the chemical composition of nearly 2000 particles of cometary origin was analyzed using a mass spectrometer, and the amount of material ejected from the nucleus was evaluated as 5-10 t/s.…”

“…Density distribution in a hypervelocity collision of a copper impactor with the comet surface of solid ice (a), porous ice (b), moist solid sand (c) and porous moist sand (d) at 100 ms 2. The spatial position of observer is identical for selected moment of time.…”