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Galileo NIMS Observations of Fragment G Impact


Direct observations of impact G by Galileo NIMS

The Galileo Near Infrared Mapping Spectrometer team has detected the G impact in data played back from the spacecraft between September 29 and October 2. Full disk spectra of Jupiter and the impact site were obtained at 17 wavelengths between 0.7 and 5.0 microns, every 5 1/3 seconds. First evidence of the impact was seen in a spectrum taken at 07:33:37 UT on 18 July. The impact is seen in subsequent samples every 5 1/3 seconds until 07:34:03 and every 10 2/3 seconds following that until 7:34:35 (intermediate observations were not played back at this time). The observed excess IR emisison slowly reddens over this period, which we interpret as cooling of the fireball from the explosion.

A very preliminary analysis of one spectrum at 07:33:48 is interpreted as a 2400 K fireball cloud, 30 km in diameter. Atmospheric absorption features are seen in the black body spectrum, which we interpret to mean that the fireball is still in the Jovian atmosphere.

The times above are all corrected to the time events would have been observed on Earth, if they had been visible from the Earth.

Playbacks are continuing. Another 8 samples at 10 2/3 second intervals will be returned this week. Additional G data wil be returned in the November-January timeframe.

R. W. Carlson, P. R. Weissman, M. Segura, F. Leader, J. Hui
Near Infrared Mapping Spectrometer Team

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