[Previous] | [Session 54] | [Next]
A. G. Davies (JPL), L. P. Keszthelyi (U. Arizona/HVO), R. Lopes-Gautier (JPL), A. S. McEwen (U. Arizona), W. D. Smythe, R. W. Carlson (JPL), NIMS Team , SSI Team
Infrared wavelength observations of Io by the Galileo spacecraft have shown that lavas erupting at "best-fit" temperatures up to 1825 K are common (McEwen et al., 1998). During orbit C9, both the Near Infrared Mapping Spectrometer (NIMS) and the Solid State Imaging experiment (SSI) observed an eruption at Pillan Patera. At Pillan, the level of activity was greater than had been previously observed, and would result in a spectacular "black eye" on the surface of Io. Both instruments made observations separated by about eight minutes, with the Pele/Pillan region in darkness. These observations allow thermal models to be fitted to mutually-constrained NIMS and SSI datasets and represent the best opportunity so far to tightly constrain magma liquidus temperatures for a high-temperature eruption on Io. The NIMS C9 observation has a resolution of 725 km/pixel. Pele and Pillan are therefore within one pixel, and the NIMS spectrum represents the combined spectra of both hot spots. The shape of the spectrum shows a marked shift to shorter wavelengths, different to every other hot spot imaged by NIMS (for examples, see Davies et al., 1998). According to output from models of thermal emissivity from active volcanism (e.g. Davies, 1996), this indicates that the bulk of the emitting surface is at high temperatures, in excess of 900 K, for one on the hot spots, most likely Pillan. The age of these volcanics is only a few minutes, yet cover several square kilometers in area. Clearly, a vigorous style of volcanic activity is taking place where there is an unusually high amount of thermal emission at short wavelengths: suitable candidates for eruption style are fire fountains or a rapidly overturning lava lake. In this respect, this eruption is akin to those observed by Blaney et al, (1995), and Stansbury et al, (1997). A turbulent flow may exhibit the same thermal signature if the crust on the surface is constantly disrupted.
Blaney et al., (1995) Icarus, 113, 220-225. Davies (1996) Icarus, 124, 45-61. Davies et al., (1998) Submitted to Icarus. McEwen et al., (1998) Science, 281, p89-87-90. Stansbury et al., (1997) GRL, 24, 2455-2458.