“…Therefore, primordial dust and ice would remain only local regions well below the surface and well above the center of the nucleus (e.g., Jewitt, 1992;Meech, 2000;Prialnik et al, 2004Prialnik et al, , 2008. This scenario, which is hereafter called the standard model, has turned out to describe well the nucleus of Comet 9P/Tempel 1 (T1), the target of NASA's Deep Impact (DI) mission: (1) a low thermal inertia of its surface estimated from thermal maps of the nucleus indicates the presence of a dust mantle ; (2) the existence of large grains in a dust trail along the trajectory of the comet would result from the preferential elimination of small-sized dust during the formation of a dust mantle (Sykes and Walker, 1992;Reach et al, 2007); (3) the optical and infrared properties of dust excavated by the DI event are explained well by the existence of a dust mantle composed of compact aggregates, below which fluffy aggregates are also embedded with icy volatiles (Yamamoto et al, 2008); (4) near-infrared spectroscopic observations of volatiles excavated by the DI event revealed thermal processing of icy layers below a dust mantle (Mumma et al, 2005); (5) the sublimation rate of 6 × 10 27 water molecules s −1 (∼180 kg s −1 ) from the T1 nucleus before the DI event implies that the top surface of several meters could have been lost simply by the sublimation process (e.g., Schleicher et al, 2006). In addition, the standard model has been supported by numerical studies on thermal evolution of the T1 nucleus: the formation of a dust mantle with chemical differentiations of the T1 nucleus (De Sanctis et al, 2007); a crystalline ice crust with a thickness of 40-240 m below a dust mantle (Bar-Nun et al, 1989).…”