We posted a similar image of an Io and Europa mutual event from the New Horizons mission a few years back when it zipped past Jupiter on its long journey to Pluto. Our hero of freelancer image compositing Gordan Ugarkovic now presents to us a much better view.
I count at least 4 if not 5 active eruption on Io in this version. The level of detail improvement from the same encounter is amazing. Old missions keep getting newer.