DPS 2001 meeting, November 2001
Session 5. Cassini and Galileo at Jupiter II
Oral, Chairs: R. Lopes, A. Simon-Miller, Tuesday, November 27, 2001, 2:00-3:20pm, Regency E

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[5.08] Temperatures of Io's Pele hotspot from Cassini eclipse images

J. Radebaugh, A. S. McEwen (University of Arizona)

Cassini's flyby of the Jupiter system in December 2000 and January 2001provided us with three sets of images of Io in eclipse by Jupiter. Taking the ratio of fluxes through the clear and 1 micron filters yields hotspot temperatures. These wavelengths are sensitive to the highest-temperature components, corresponding to lava exposed to the surface within ~10 minutes of each observation. Pele, often seen as an active hotspot and plume source by Voyager, Galileo, and ground-based observers, showed maximum temperatures of 1500 K +-70 K and minimum temperatures of 1300 K +- 40 K, over three eclipses observed by Cassini. Temperatures from 26 eclipse image pairs were typically about 1370 K, which is consistent with previous temperature measurements of Pele.

Cassini's high data rate made it possible to view change in Pele's temperatures over short time scales; ten image pairs per eclipse were taken approximately 11 minutes apart. Temperatures during the first half of the first eclipse were relatively constant, then they varied over at least 100 K over several tens of minutes. Temperatures for the last eclipse showed a similar pattern of being relatively constant for the first half, then varying over at least 30 K near the end of the eclipse, when the view of Pele was more oblique. We also observed that the total intensity falls off at about cosine(emission angle)1.6, consistent with exposure of the hottest material in cracks and low areas.

Pele has been postulated to be an active lava lake, based on Galileo observations of consistently high temperatures, shape of the thermal emission spectrum, lack of extensive lava flows, and possible presence of a glowing lava lake margin. These new Cassini measurements of consistently high temperatures (with small variations) may be explained by a vigorously and continuously overturning lava lake.

The author(s) of this abstract have provided an email address for comments about the abstract: jani@LPL.arizona.edu

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