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H.E. Matthews (NRC Canada &\ JACH), A. Marten, R. Moreno (DESPA, Meudon), T. Owen (IfA, Hawaii)
Since the collision of the fragments of Comet Shoemaker-Levy 9 with Jupiter in July 1994 we have monitored molecular species, undetected before the collision, in the jovian stratosphere at submm wavelengths using the James Clerk Maxwell Telescope.
Observations of the J=4--3 transitions of HCN, H13CN and HC15N and J=7--6 lines of CS, C32S, C34S were obtained at the equatorial limbs of Jupiter in September 1998. From these data we are able to show that these species exist in a regime characterised by pressure p < 0.2~mbar, and temperature T = 164±2~K. We place the following extreme limits on mixing ratios, allowing for all known sources of error in the atmospheric model (T,p), and measurement calibration errors (assumed to be 10%): q(HCN)=(3.0--4.5)\times10-8, q(H13CN)=(1.1--1.7)\times10-10, q(HC15N)=(1.0--2.6)\times10-11, q(CS)=(0.5--1.5)\times10-8, and q(C34S)=(1.2--2.4)\times10-10. Assuming no differentiation during the formation of the isotopes we derive the isotope ratios to be (relative to the terrestrial values in parentheses): 12C/13C = 2.0--4.6 (89), 14N/15N = 4.3--16.7 (270), and 32S/34S = 0.9--5.4 (23). These results indicate that the isotopic ratios in the jovian stratosphere are very different from terrestrial. First, the jovian 12C/13C value found deeper in the atmosphere by the Galileo probe in 1995 is closely terrestrial, whereas our determination is about 3 times this value. Further, the present 14N/15N ratio is even higher than that derived from ISO-SWS observations of NH3 (Foucet et al., 2000), while a closely terrestrial result was derived by Jewitt et al (1997) from HCN observations of Comet Hale-Bopp. All our results imply either that the isotopic ratios were very peculiar in Jupiter's atmosphere during the crash of SL9 and/or that the composition of SL9 was very different from that of known comets.