Subaru/COMICS mid-infrared spectroscopic observations of the dust plume from comet 9P/Tempel

Abstract

We carried out mid-infrared observations of the Deep Impact (DI) collision with a Jupiter-family (JF) comet, 9P/Tempel, using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2 m Subaru Telescope. The N-band spectrum (8-13 μm; R ∼ 250) of the dust ejecta from the comet nucleus 3.5 hours after the DI event shows a strong crystalline silicate feature. The Subaru/COMICS observation also reveals that small (< 1 μm) amorphous pyroxene and carbon-rich grains flew away in the forefront of the ejecta plume before our spectroscopic observation, leaving behind relatively large submicron (0.8-1 μm) crystalline particles that we subsequently observed. The submicron grains within the subsurface layer of comet 9P/Tempel's nucleus have a higher crystalline-to-amorphous silicate ratio than that in the comae of other JF comets, and even that of Oort cloud comets. Near the comet nucleus 3.5 hours after the impact the crystalline-to-amorphous ratio is similar to that of Hale-Bopp coma dust at 0.97 AU. © 2009 Springer-Verlag Berlin Heidelberg.