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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