Observations of water in comets with Odin

The Odin satellite, which can observe the 1 1 0 -1 0 1 rotational line at 557 GHz of ortho water with a high spectral resolution (80 m s - 1 ) and a spatial resolution of 2.1', is well suited for cometary studies. The intensity of this line provides an estimate of the water production rate. The line width gives a direct measure of the coma expansion velocity. The line centre position and shape are affected by the anisotropy of the outgassing and by optical depth effects. Comets observed with Odin up to now are C/2001 A2 (LINEAR) during the commissioning phase of the satellite, 19P/Borrelly at the time of the Deep Space 1 flyby, C/2000 WM 1 (LINEAR), and 153P/2002 Cl (Ikeya-Zhang). For this last comet, thorough observations were made at the moment of its closest approach to Earth at the end of April 2002. A deep integration resulted in the detection of the 1 1 0 -1 0 1 line of H 2 1 8 O at 548 GHz. No 1 6 O/ 1 8 O isotopic anomaly is found.