From a distance of 17,000 km the indefatigable spacecraft captured closeup images of the lava fountain, despite being blasted by a heavy dose of radiation just before the encounter. Astronomers making Earth-based telescopic observations see a bright spot like this one somewhere on Io only about 20 percent of the time, so the Galileo team was fortunate to catch one in its narrow field of view. North is to the upper left of the picture and the Sun illuminates the surface from the lower left. The intense volcanism on Io results from 100 meter high tides raised in its otherwise solid surface by nearby Jupiter and the other Galilean satellites. Although this process is fairly well understood, many aspects of Io's forbidding environment remains a mystery.
Many basic questions are still unanswered.
The fact that the same eruption was recorded by Galileo and by an Earth-based infrared telescope is a boon to the research being done on Io. By combining the data, scientists have their best chance ever to pin down temperatures of Io's extremely hot lava. Lavas we see now on Earth are about 300 K cooler than they used to be. It's very surprising to see lava flows on Io as hot as these ancient flows on Earth. Simply because Io's soil has been reworked many, many times, so the melting temperature should be lower for the same reason that Earth's basalts melt at a lower temperature.