Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p21b..04f&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P21B-04
Physics
5700 Planetary Sciences: Fluid Planets, 5704 Atmospheres (0343, 1060), 5709 Composition (1060), 6255 Neptune, 6275 Saturn
Scientific paper
We discuss how new observations of far-infrared rotational lines of HD and mid-infrared vibrational features of CH3D are challenging the accepted measurements for the deuterium abundance in the outer solar system. New derivations of D/H will be presented from the Cassini Composite Infrared Spectrometer (CIRS) for Saturn, the Spitzer Infrared Spectrometer (IRS) for Uranus and Neptune and the grism mode of the AKARI Infrared camera (IRC) for Neptune. Many thousands of spatially resolved Cassini/CIRS spectra at an unapodized spectral resolution of 0.25 cm-1 covering a variety of latitudes on Saturn have been acquired during Cassini's prime mission, and are coadded to give ten independent estimates of the HD mole fraction and hundreds of estimates of the CH3D mole fraction. Spitzer/IRS acquired disc-averaged spectra of Uranus during Cycle 1 and more recently with Director Discretionary time in December 2007. Neptune disc-averaged spectra were acquired during Cycle 2 (November 2005). ISAS/JAXA's AKARI satellite recorded disc-integrated spectra of Neptune in May 2007 with a resolving power of 50 in the 5.5-13 micron range. These spectra have been analysed using two separated radiative transfer and retrieval models to check for consistency of results. On Saturn, we retrieve lower estimates of D/H from HD and CH3D than were obtained from ISO/SWS by Lellouch et al. (2001). Preliminary analysis of Uranus spectra suggest that the CH3D/CH4 ratio is significantly smaller than that predicted by the HD abundance determined from ISO/SWS by Feuchtgruber et al. (1999), suggesting a Uranian ratio more like that of Saturn, or a substantially different fractionation factor from that in the current literature. Furthermore, although constraints on CH3D from mid-IR Neptune spectroscopy are weaker, preliminary findings are that the CH3D/CH4 ratio is lower than that obtained by Orton et al. (1992) and inferred from HD measurements from ISO/SWS (Feuchtgruber et al., 1999). Fletcher is supported by an appointment to the NASA Postdoctoral Program at the Caltech/Jet Propulsion Laboratory, administered by Oak Ride Associated Universities through a contract with NASA.
Burgdorf Martin
Fletcher Leigh N.
Irwin Patrick G.
Line Michael R.
Mainzer Amy
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