Elsevier

Icarus

Volume 169, Issue 1, May 2004, Pages 65-79
Icarus

Observations and temperatures of Io's Pele Patera from Cassini and Galileo spacecraft images

https://doi.org/10.1016/j.icarus.2003.10.019Get rights and content

Abstract

Pele has been the most intense high-temperature hotspot on Io to be continuously active during the Galileo monitoring from 1996–2001. A suite of characteristics suggests that Pele is an active lava lake inside a volcanic depression. In 2000–2001, Pele was observed by two spacecraft, Cassini and Galileo. The Cassini observations revealed that Pele is variable in activity over timescales of minutes, typical of active lava lakes in Hawaii and Ethiopia. These observations also revealed that the short-wavelength thermal emission from Pele decreases with rotation of Io by a factor significantly greater than the cosine of the emission angle, and that the color temperature becomes more variable and hotter at high emission angles. This behavior suggests that a significant portion of the visible thermal emission from Pele comes from lava fountains within a topographically confined lava body. High spatial resolution, nightside images from a Galileo flyby in October 2001 revealed a large, relatively cool (<800 K) region, ringed by bright hotspots, and a central region of high thermal emission, which is hypothesized to be due to fountaining and convection in the lava lake. Images taken through different filters revealed color temperatures of 1500±80 K from Cassini ISS data and 1605±220 and 1420±100 K from small portions of Galileo SSI data. Such temperatures are near the upper limit for basaltic compositions. Given the limitations of deriving lava eruption temperature in the absence of in situ measurement, it is possible that Pele has lavas with ultramafic compositions. The long-lived, vigorous activity of what is most likely an actively overturning lava lake in Pele Patera indicates that there is a strong connection to a large, stable magma source region.

Section snippets

Introduction and previous discoveries about Pele

Jupiter's moon Io lays claim to the hottest and most active volcanoes in the Solar System. Of the many volcanoes littering Io's surface, Pele Patera is one of the most distinctive and dramatic in its eruption style, activity level, and appearance Smith et al., 1979, Spencer and Schneider, 1996, McEwen et al., 1998a. During the Voyager 1 flyby in 1979, Pele Patera was observed to be the source of a giant, 1200 km diameter, diffuse, red ring of deposits (Fig. 1), produced by a plume reaching

New observations

The main objective of this paper is to present the latest spacecraft observations of Pele Patera. In this section, we describe these data and briefly explain how we derive lava temperatures. While most of the details of the data analysis are in the appendices, it is important to note that these temperatures could only be retrieved with such precision because of the exquisite calibration of the cameras on both Galileo and Cassini. Most of the techniques we use have not been applied to

Continuous energy output

The consistently high thermal output that was seen in all previous observations of Pele continued during both the Cassini and the Galileo I32 observations. Color temperatures of ∼1350 K were seen throughout the 87 hour duration of the Cassini observations, and Galileo observed that >5 km2 of the Pele region were at about 1270±100 K, with some smaller areas being even hotter. Rough estimates of the total thermal output of Pele, based on short-wavelength emission obtained during the Galileo I32

Implications for Io's interior

At 30 km×20 km, Pele is an extremely large volcano-tectonic depression by Earth's standards (Pike and Clow, 1981). Only the giant silicic calderas approach these dimensions, but they are not filled with mafic or ultramafic lava lakes. Thus Pele does not have a comparably sized terrestrial analog. Pele is similar to many other Ionian paterae in that they appear to also have been filled with lava during some stage of their evolution Radebaugh et al., 2002, Lopes et al., 2004. Their great sizes

Conclusions

Two exceptional data sets were analyzed to obtain information about the eruption style and temperature of the Pele volcano on Io. We found color temperatures for Pele as high as 1500±80 K from Cassini and 1605±220 K or 1420±100 K from Galileo I32. Actual lava temperatures could be hundreds of degrees higher, so compositions ranging from basaltic to ultramafic should be considered for Pele's lavas. The high temperatures, their variation over all timescales, and the decrease in brightness with

Acknowledgements

The authors express their thanks to Paul Geissler for his help with Cassini image processing. This material is based upon work supported by the National Aeronautics and Space Administration under Grant Nos. NAG5-10166 and NAGW5-3632 issued through the Planetary Geology and Geophysics Program, and by the Cassini project. Ashley Davies is supported by Grant No. 344-30-23-09 through the NASA Planetary Geology and Geophysics program. All images were processed at PIRL, the Planetary Image Research

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