Silicate cooling model fits to Galileo NIMS data of volcanism on Io

The Near Infrared Mapping Spectrometer (NIMS) has obtained spectra of volca noes on the surface of the jovian satellite Io. Fits to data using a silica te cooling model allow us to constrain lava eruption rates and eruption age . The thermal signatures of the hot spots are indicative of active and cool ing silicate lava flows. For large, active hot spots maximum ages of how su rfaces detected by NIMS typically range from days to months, although in on e case it is nearly 30 years. Mass eruption rates for the main hot spots ar e in the range 7 m(3) s(-1) to 79 m(3) s(-1), using an average how thicknes s of 1 m. These mass eruption rates are orders of magnitude less than those implied for large thermal outbursts on Io: the eruptions observed during J une 1996 are most likely of a different eruption style, on a much smaller s cale. The observation analyzed here may he representative of the current ba ckground level of volcanic activity on the anti-jove hemisphere of Io. The global mass eruption rate from these "non-outburst" hot spots is calculated to be 43 km(3)/year, equivalent to a global resurfacing rate of about 1 mm /year, about 10% of the minimum required global resurfacing volume. The tot al observed energy output from the 14 hot spots analyzed is 3.6 x 10(12) W. Normalized globally, these hot spots contribute approximately 10% of Io's radiometric heat flux.