Thermal emission from lava flows on Io

The thermal emission from Loki, Ulgen, and Amaterasu Paterae can be modeled remarkably accurately with a simple two-parameter model based on analytical expressions for the cooling of a silicate lava flow. In this model the Row is assumed to produce new surface at a constant rate and then the surface cools purely by radiation. The highly nonlinear (T-4) dependence of radiative flux on temperature paradoxically produces simple approximations for the temperature of the surface vs time and also for the distribution function which gives the fraction of the surface at any given temperature. This work is based upon a modification of the Stefan model which describes the solidification of lava flows. The first of the two parameters which describe the system, R-A', is the product of a flow rate R-A (given in m(2) sec(-1)) and a term set by material properties and related to thermal inertia. The second parameter t(0)' is the product of a time scale t(0) and another term set by material properties. The time t(0) can be interpreted either as the time the flow has been active or the time it takes for old surface to be covered by new flow. The analytical model predicts a spectrum with F-A proportional to lambda(3) in the near infrared, with an exponential cutoff at short enough wavelengths and a slower turnover at long wavelengths. Slightly more elaborate versions of the model predict the way in which the spectrum should change when the flow rate varies with time. Measurements of such variations will provide a critical test of the model. (C) 1997 Academic Press.