Shoemaker-Levy 9: Temperature, Diameter and Energy of Fireballs

Astronomy and Astrophysics – Astronomy

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Scientific paper

The temporal and spectral variation of light emitted during the impacts of Shoemaker-Levy 9 fragments provides information about temperature, size, and emitted energy in the early fireball stage. Based on Galileo remote sensing data, the spectral distribution peaks in the violet to blue range within the first 5 seconds, moves through the visible to 1 mu m within 20 seconds, and to 2 mu m within 40 seconds. This distribution is modelled by the product of a solid angle representing a growing fireball and a blackbody radiance term. Spectrally varying reflection from an underlying cloud deck is a significant factor. Further analysis of the Galileo Photopolarimeter Radiometer (PPR) data for the Q1 impact, observed at both 678 and 945 nm, yields color temperatures and energy information for the first 12 seconds of the event with a 1.5 sec time resolution. The flash is initially brighter at 678 than at 945 nm. The corresponding initial temperature, dependent on the relative calibration of the two PPR channels, is computed at 24000 K. Compared to the G event, Q1 cooled faster and expanded slower. If G had been observed by Galileo 2 sec earlier it would likely have shown a higher temperature, consistent with Q1. The total radiant energy emitted during the fireball phase is estimated at 3.2 x 10E24 ergs for Q1 and 8.4 x 10E24 ergs for G. For G, this is equivalent to the kinetic energy of an initial mass of 4.7 x 10E11 gm, forming a lower limit to the mass of that fragment. Total energies for events H and L may be inferred from the Q1 and G calculations. Ref. T.Z. Martin et al, Science vol. 268, 1875 (1995).

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