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J. A. Rathbun (Univ. of Redlands), J. R. Spencer (SwRI)
Io is the most volcanically active body in the solar system and Loki is the largest and most powerful volcano on Io. The Galileo spacecraft was unable to observe Loki often at high resolution, so most of the data on Loki is from groundbased observatories. Loki's infrared brightness has been measured from the ground on approximately a monthly basis since 1989, with the most data taken at NASA's Infrared Telescope Facility (IRTF). Using that data, we found that from 1989 through 2001 Loki's eruptions were periodic, not merely episodic as previously thought, with a period of about 540 days. More recent data, taken exclusively at IRTF, show that Loki's brightness is no longer varying from "high" to "low" in a regular manner, but is more consistently at a moderate brightness. We can explain this change in behavior by invoking a lava lake model for Loki. We model Loki as a deep, rectangular cavity filled with liquid magma. As the magma cools it solidifies and its density increases until it is negatively buoyant. At that point, the crust sinks, exposing new lava. The neighboring piece of crust then sinks, and the next, until the entire surface of the lake has been resurfaced. We model the temperature of the surface as a function of position and time, and, assuming blackbody emission, calculate the infrared brightness of Loki. We compare the modeled brightnesses with those measured from our groundbased observing campaign. This simple model quantitatively matches the 3.5 micron brightnesses measured. We find that the brightness depends on the rate at which this resurfacing wave covers the entire surface. By decreasing the rate by a factor of two we can match the more recent observations.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.