The Hot Spot of the Solar System

If you go outside tonight and look for the first star you see to wish upon,it's quite likely that you'll end up wishing on a planet. The giant of the solar system, Jupiter, dazzles the sky from sunset until well after midnight. To find it, look high in the south-southeast. Binoculars will show the four large Galilean moons (named after their discoverer, Galileo Galilei.) They are Io, Europa, Callisto and Ganymede. If you are able to see the moons, Io is the one closest to Jupiter. Thinking about these worlds, so very much farther from the Sun than the Earth, one would think of bitter, bitter cold, but such is not the case. Io, a world which has a reputation for surprises, is now known to be the hot spot of the solar system.

Io is a small world, 3620 km in diameter and orbits Jupiter at a distanceof 422,000 km. in only 1.7 days. Such a small moon orbiting so close to such a large planet has dire consequences for Io.

Io has a density a little over half that of Earths. This indicates that it ismostly composed of rocky material with some ice and slush. This seems a bit strange because Io's surface shows no impact craters. Rocky worlds show at least some impact craters. As it turns out, the surface appears to be a sulfur desert with sulfur ash raining down from the sky. This sulfur ash rain results from Io's active volcanoes. Io was the first world other than Earth where active volcanism was known to exist.

The Voyager I spacecraft encountered Jupiter's moons in 1979 andastronomers were shocked when images of Io showed erupting volcanoes! Currently it is the Galileo spacecraft in orbit around Jupiter that is studying the moons.

Io''s volcanoes are not caused by the same thing that causes volcanoeshere on Earth. It is tidal heating that creates volcanoes on Io. Europa and Ganymede affect Io's orbit, causing it to be slightly elliptical. This makes Io's distance from Jupiter vary and this causes Io to be  pushed  and pulled  from several directions! It is this flexing that causes heat to be generated in Io's interior which in turn melts rocks and causes this melted material to rise to the surface. This rising hot rockmelts the sulfur above and causing sulfur and sulfur dioxide gas to vent through the surface, as a volcano. We see the liquid and solid sulfur as well as the white frost of sulfur dioxide gas that coat Io's surface.

The Galileo spacecraft has returned many images of Io and it is with greatfascination that astronomers compare these pictures with those of Voyager nearly 20 years ago. Just in that amount of time, some volcanoes which had been active have become dormant, while new eruptions have also been identified.

Galileo has recently returned even more amazing information about thistiny world. The spacecraft has conducted infrared observations of Io and has shown at least a dozen volcanic vents spewing forth lava at temperatures ranging from 2200 degrees F to 3100 degrees F! These temperatures are more than three times hotter than the highest temperatures recorded on Mercury: the planet closest to the Sun.Io is not only a world turning inside out, it is now awarded the hot spot in the solar system!