The following document lists the file abstract/ELELLOUC_DEUTJS.abs
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We propose to observe the HD R(2) (37.702 micron) line on Jupiter and Saturn with SWS. The goal is to complement the LWS measurements of the HD R(0) and R(1) lines at 112 and 56 microns, that will be performed in the central program, to improve the accuracy of the determination of the D/H ratio in these two planets. The D/H abundance in Jupiter and Saturn is thought to be representative of the conditions in the primitive nebula from which the Solar System was formed. As such, it is a key parameter constraining (i) models of galactic evolution (ii) physical conditions prevailing in the solar nebula (iii) the origin and history of the grains embedded in the nebula. So far (and besides the very recent in situ measurement by the Galileo Probe in Jupiter), the D/H ratio in Giant Planets has been measured spectroscopically from visible lines of HD and infrared features of CH3D. Important complications are associated with both methods, however. ISO offers a unique opportunity to improve significantly the D/H determination by giving access to the rotational lines of HD in the far infrared range. Preliminary analyses of the HD lines observed by ISO in technical time show however that cloud opacity and thermal profiles effects in the planetary atmospheres must be carefully considered when deriving the D/H ratio. It thus appear necessary to observe so many HD lines as possible (i.e. three) to disentangle betwen the various effects. The S(0) and S(1) quadrupolar line of H2 near 28.2 and 17.0 micron will also been observed to constrain the Jupiter's and Saturn's thermal profile, facilitating the interpretation of the HD measurements.