Infrared spectral observations of comet 103P/Hartley 2 by ISOPHOT

Abstract

Spectral observations in the 2.5-12 mu m range of comet 103P/Hartley 2 were performed on 1 Jan. 1998 by the ISOPHOT instrument, on board the Infrared Space Observatory. The obtained spectrum evidences intense bands at 2.66 and 4.26 mu m, attributable to H_2O and CO_2, respectively. The derived molecular production rates are Q(H_2O) = (3.1 +/- 0.2) x 10(28) molec. s(-1) and Q(CO_2) = (2.5 +/- 0.3) x 10(27) molec. s(-1) . This leads to a CO_2/H_2O abundance ratio of ~ 8%, showing that P/Hartley 2 is a relatively CO_2 abundant comet, with respect to 1P/Halley and several other comets. A feature has been detected at 3.69 mu m, whose attribution is rather puzzling. The long wavelength part of the spectrum is well fitted by a black-body profile at 285 K colour temperature. No significant silicate emission feature around 10 mu m is observed, within observation errors. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with participation of ISAS and NASA.