Charting thermal emission variability at Amirani with the Galileo NIMS Io Thermal Emission Database (NITED)

Abstract We have examined the variability of thermal emission from lava flows at Amirani on Io, using measurements of radiant flux from detections by the Galileo Near Infrared Mapping Spectrometer (NIMS) between 1996 and 2001. Amirani is the longest currently active lava flow field in the Solar System and a persistent thermal source in every Galileo NIMS observation that covers its location. We have quantified the thermal emission from hot spots correlated with discrete areas of new lava flow emplacement at points along the length of the Amirani flow field in high spatial resolution NIMS observations in 2000 and 2001. Where discernible, the position of some effusive activity changes from orbit to orbit. We find the implied style of emplacement of lava at Amirani is consistent with pahoehoe-like flows. There is an estimated 50% decrease in discharge rate between 1997 and late 2001, perhaps linked to an outburst eruption in the Amirani vicinity in February 2001. The variability of thermal emission from Amirani is less than that seen at a number of other persistently active ionian volcanoes (such as Prometheus, Culann, and Loki Patera). All of these volcanoes exhibit large increases and decreases in the absolute magnitude of thermal emission (see Matson et al., 2006 [Loki Patera]; Davies, A.G. et al. [2006] . Icarus 184, 460–477 [Prometheus]; and Davies, A.G., Ennis, M.E. [2011]. Icarus 215, 401–416 [Culann]). At Amirani, as at these volcanoes, the thermal emission measured between 1996 and 2001 indicates a persistent, although variable, supply of magma to the surface. In high spatial resolution NIMS observations of hot spots obtained in 2000 and 2001 we estimate the emitted power from active lava flows associated with Amirani to be ∼170 ± 30 GW, which corresponds to total effusion rates (assuming a basaltic composition) from multiple points along the Amirani flow of 34–56 m 3 /s.