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Water Detected in Fragment G & K


We have detected cometary water in the fireball of fragments G and K immediately after the plume became visible to observers on Earth. The observations were performed using the Kuiper Echelle Grating Spectrometer (spectral resolving power 9000; 5" slit) on the Kuiper Airborne Observatory. The G fireball was observed at about July 18.323 UT; the K fragment fireball was observed on July 19.444. Three H2O lines were observed in emission for both the G and K fireballs at the following wavelengths: 7.7136, 7.7118, and 7.7090 microns. Numerous jovian 12CH4 and 13CH4 lines were observed in emission across our bandpass (7.671-7.722 microns). This serves as a thermometer of Jupiter's stratosphere, sounding the 1-microbar to 10-millibar levels. The radiance in the jovian CH4 lines increased by a factor of about 25-30 between the pre-crash level and the peak of the fireball. The CH4 lines were observed to decay over the next 2 hr. The three H2O lines have a distinctively different time behavior: they essentially disappear over a 30-min period. Very high temperatures (T > 500 K) are required to observe these H2O transitions. The observing geometry, high temperature, and short time scale for the disappearance of these H2O lines favor a cometary (rather than jovian) source. This, in turn, would confirm that P/Shoemaker-Levy 9 was a comet and not an asteroid.

G. Bjoraker, Goddard Space Flight Center, NASA; and T. Herter, S. Stolovy, G. Gull, and B. Pirger, Cornell University

August 13, 1994

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