Comet P/Gehrels 3: Spectroscopic Investigation and Thermal Modeling

Comet P/Gehrels 3 has a particular orbit with a high Tisserand invariant allowing very effective Jupiter encounters. This implies that the comet spends part of its life as a temporary satellite of Jupiter (Carusi et al., 1996, Electronic Atlas of Evolution of Short Period Comets, http://titan.ias.fra.cnr.it/ias-home/ias-home.html). We performed spectroscopic observations of P/Geherls 3 in order to investigate this Jupiter family comet and to increase the knowledge on cometary nuclei and the relationships between comets and asteroids. The comet P/Gehrels 3 has been observed at the Mauna Kea Observatory on June 20, 1996 with the CFH 3.6 m telescope equipped with the Multi Objects Spectrograph and the CCD STIS2 (2048x2048 pixel). The spectral range covered is about 0.38 < lambda < 1 mu m and the obtained spectrum is redder than the solar one. The computed reflectivity gradient S' is equal to 13.3 %/10(3) Angstroms in the wavelength range 0.55-0.80 mu m, and it is very similar to the average of those of D-Type asteroids (Lazzarin et al., 1995, Astron. J., 110, 1). A thermal model (Capria et al, 1996, PSS, in press) of this comet has been computed in order to study the evolution and the behaviour of this object during the epoch of observation. Preliminary results indicate the formation of a stable crust on the surface of the object.