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Galileo observations of the impacts

Published online by Cambridge University Press:  02 August 2016

Clark R. Chapman
Clark R. Chapman*
Affiliation:
Planetary Science Institute, 620 N. 6th Avenue, Tucson AZ 85705

Abstract

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Galileo observations in the UV, visible, and infrared uniquely characterize the luminous phenomena associated primarily with the early stages of the impacts of SL9 fragments—the bolide and fireball phases—because of the spacecraft's direct view of the impact sites. The single luminous events, typically 1 min in duration at near-IR wavelengths, are interpreted as initial bolide flashes in the stratosphere followed immediately by development of a fireball above the ammonia clouds, which subsequently rises, expands, and cools from ∼ 8000 K to ∼ 1000 K over the first minute. The brightnesses of the bolide phases were remarkably similar for disparate events, including L and N, which were among the biggest and smallest of the impacts as classified by Earth-based phenomena. Subsequent fireball brightnesses differ much more, suggesting that the similar-sized fragments were near the threshold for creating fireballs and large dark features on Jupiter's face. Both bolides and fireballs were much dimmer than had been predicted before the impacts, implying that impactor masses were small (∼0.5km diameter). Galileo data clarify the physical interpretation of the “first precursor,” as observed from Earth: it probably represents a massive meteor storm accompanying the main fragment, peaking ∼10s before the fragment penetrates to the tropopause; hints of behind-the-limb luminous phenomena, recorded from Earth immediately following the peak of the first precursor, may be due to reflection of the late bolide/early fireball stages from comet debris very high in Jupiter's atmosphere.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 156: The Collision of Comet Shoemaker-Levy 9 and Jupiter , May 1996 , pp. 121 - 132
Copyright
Copyright © Cambridge University Press 1996

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