Io: Heat flow from small volcanic features

We identify nine new faint thermal sources on Io via color ratio images constructed from relatively high spatial resolution Galileo NIMS data acquired late in the mission. All of these identifications are associated with small dark paterae. We utilize NIMS data to quantify their volcanic thermal emission as ~0.53×10¹²W (or ~0.5% of Io's total heat flow). In addition, we refine our previous estimates of the thermal emission from 47 hot spots and highlight several hot spots within the Amirani flow field.Small dark paterae still out-number faint (close to the limit of detection) hot spots identified in high spatial resolution multi-wavelength NIMS data. In particular, we point out 24 small dark paterae that were scanned by NIMS (at resolutions down to ~17. km/pixel) but had no detectable volcanic thermal emission. All dark paterae are expected to have some volcanic thermal emission, but the small size and finite number of detectable faint sources limit their contribution to the total heat flow on Io. Compared to small paterae, small dark flows are more numerous but must have significantly lower surface temperatures.Finally, we update and summarize our results for the global heat flow on Io due to 242 recently active volcanic features including other dark paterae as well as large dark flows. The volcanic thermal emission from known hot spots, undetected (scanned) dark patera and outbursts can account for only ~56.2×10¹²W (or ~54%) of Io's total heat flow. Approximately 49×10¹²W (or ~46%) of Io's heat flow remains an enigma.