Take a nice long look at this beautiful image of Io, the most volcanically active world in our solar system! This was assembled by Ted Stryk from Voyager 1 images, taken as the spacecraft  passed by on March 4, 1979. At 2,263 miles (3642 km) wide Io is the third largest of Jupiter’s moons and is one of the four Galilean moons easily visible from Earth with even a small telescope or binoculars. (The others being Callisto, Europa and the giant Ganymede.) Io is constantly being resurfaced by volcanic eruptions that ooze sulfuric lavas and spray plumes of material across its terrain. The energy for these eruptions comes from powerful tidal forces exerted by the giant planet Jupiter and Io’s neighboring moons Europa and Ganymede. As Io orbits Jupiter in its elliptical orbit it is being pulled in different directions by the gravity of these other worlds…the resulting gravitational forces cause its surface to rise and fall by as much as 330 feet! This generates a lot of frictional heating within the moon and keeps its interior molten. Any meteorite impacts are quickly filled in by lava, hence the lack of  craters on this moon!

In addition to this, Io is also traveling through Jupiter’s extremely powerful magnetic field. This field strips material from Io at a rate of 1 ton every second, sending it into orbit around Jupiter and electrically charging it to create a doughnut- or innertube-shaped field (called a torus) of plasma in which Io resides. This field in turn acts to expand Jupiter’s already powerful magnetosphere, so the whole thing acts as a positive-feedback loop. Some of the plasma spirals in to Jupiter’s atmosphere to help create huge aurorae and powerful lightning.

Ted’s image of Io above is a rework of an earlier version he posted in August of last year. Jupiter’s terminator line – the divider between night and day – can be seen in the background. Check out this and more great images on his blog Planetary Images From Then and Now. And for more detail about Io and its amazing surface features be sure to visit Jason Perry’s Io-dedicated site The Gish Bar Times.

Image © Ted Stryk. (Raw image data courtesy NASA / JPL)