This orbiter had a significant early problem when its main antenna refused to deploy. The next visitor to Jupiter was the Galileo orbiter in 1995. Power for this probe came from a radioisotope thermal generator on the boom at the upper center. However, reprogramming of spacecraft and judicious use of mission planning led to a very successful mission. This led to significant loss of planned photography. Painting of Galileo spacecraft at Jupiter. Both Voyagers are still active, recently departing the heliosphere. Comparisons between images taken on both flybys showed that seven of the nine plumes were still active, with a single volcano shutting down in the four months between flybys. This activity was predicted by a paper published by Peale et al shortly before the encounter. ![]() Voyager 1 images showed nine active plumes. Both spacecraft took the first photos close enough to Io to show actual volcanoes in eruption with active plumes. Voyager 1 and 2 flew by Jupiter on their way outbound to the Grand Tour of the gas giants of the outer solar system. Close-up images by Pioneer 10 were lost due to the intense radiation environment. The only good photo of Io was taken by Pioneer 11. Trajectory analysis showed that Io was the densest of all four satellites, with a density similar to the terrestrial planets. The flybys discovered a thin atmosphere on Io and intense radiation belts in the vicinity of Io’s orbit. These were high speed fly-bys on their way out of the solar system. The first spacecraft to pass near Jupiter were Pioneer 10 and 11 in 19 respectively. Inset is Juno Jupiter atmospheric probe currently orbiting Jupiter. I pulled the majority of these two posts from those two sources. And for some reason, the Wiki Volcanology of Io is surprisingly complete and a decent place to start. It is available on Amazon in all three formats including Kindle. Among the best is Davies’ 2007 355-page Volcanism on Io: A Comparison with Earth. There was a great explosion of publications on Io following the Galileo mission. All of this working together makes Io a very difficult place to visit due to incredibly high radiation and electrical conditions locally. The interaction between Jupiter’s magnetic field and the torus creates what is called the Io Flux Tube. Jupiter’s magnetic field sweeps through that torus every ten hour long rotation and quickly ionizes the gas into an ion plasma. Due to its low gravity, gasses easily escape and have created a torus of gas that the moon travels through. Io ejects a significant amount of sulfur dioxide (SO2) from its surface. It takes Io about 1.77 days to make a complete orbit of Jupiter. The other Galilean moons are similarly tidally locked, just like our moon. Tidal interaction with Jupiter has locked its rotation so that the same side always faces Jupiter. It interacts with Jupiter’s magnetic field, creating significant electrical charge across the surface. Io orbits Jupiter at 422,000 km, about the distance between the earth and moon. Many of the less vigorous explosions observed are thought to be lava interaction with this snow cover. SO2 is produced in large quantities and ends up as a substantial snow layer on the surface. This changed upon further analysis which demonstrates that most of the erupted material is silicic in nature. Initial observations of massive amounts of sulfur on the surface of the moon led to speculation that sulfur was the primary erupted material. ![]() This historic photo was among the first to verify active volcanism on the moon. We do not know at this time if the magma source is a magma ocean under the crust or a mantle with an appreciable percentage of melt interlaced through it.ġ977 Voyager 1 image of Io showing two active eruptive plumes. The tidal interaction between the elliptical orbits and Jupiter and the resonance between the orbits knead and heat up Io’s interior to the extent that it has sufficient eruptible magma to power these active volcanoes. It is relatively close to three other major moons also in slightly elliptical orbits. The moon is in a slightly elliptical orbit. Flybys by other probes since 1979 and telescopic observations have identified over 150 active volcanoes and perhaps 400 volcanoes in all. ![]() Volcanic activity was first discovered in 1979 by Voyager 1’s imaging team. With the possible exception of Venus, Jupiter’s innermost Galilean moon Io is the most volcanically active body in the solar system. Note lack of impact craters meaning the moon is regularly resurfaced. Orange is plume deposit around Pele Patera.
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