Astronomy and Astrophysics Letters dedicated to ISO

First detection of the 56 mu m rotational line of HD in Saturn's atmosphere


The R(1) rotational line of HD at 56.23 mu m has been detected for the first time on Saturn using the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The measurements were made using the LWS in Fabry-Perot mode in January 1996 during the ISO performance verification phase. The measured spectrum has been compared with atmospheric models to determine the HD/H2 abundance ratio. The best model fit to the measured spectrum was obtained with a D/H ratio in hydrogen of 2.3x10-5; D/H values between 1.5x10-5 and 3.5x10-5 are however also compatible with the data. This result is intermediate between the saturnian value derived from ground-based observations of methane and its deuterated isotope, and the preliminary determination of the jovian D/H ratio measured by the mass spectrometer in the Galileo probe. The initial Saturn measurements reported here will be repeated to improve the signal-to-noise ratio, and LWS observations of HD on Jupiter, Uranus and Neptune will also be made.

planets and satellites: individual: Saturn - infrared: solar system

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