| Io |
| Io is the fifth satellite of Jupiter known, as well as being its third largest and the innermost of the Galilean moons. It is slightly larger than our moon. According to mythology, Io was a maiden who loved Jupiter (Zeus), and was turned into a heifer in an attempt to hide her from his jealous wife, Hera. Io was discovered by Galileo and Marius in the year 1610. It is mostly composed of molten silicate rock. It is thought to have a core of iron, possibly mixed with iron sulfide, and has an approximate radius of 900 km. There are very few to no impact craters on Io, much to the surprise of Voyager scientists. They then concluded that Io has a very young surface. In actuality, the surface of Io was marred�by hundreds of volcanoes! Some of them are active. Some eruptions were known to have plumes up the 300 km high! This was the first real proof that other �terrestrial� bodies are hot and active. The materials coming from the volcanoes seem to be sulfur or sulfur dioxide. Within four months, between the arrivals of Voyager 1 and two, some stopped, and others were formed. Io also has lakes of molten sulfur, mountains that aren�t volcanoes, and volcanic vents. The sulfur on that moon and its compounds give reason for Io�s appearance. Even though much of Io seems to be made up of sulfur, it is too hot for the lava to be made of sulfur. One of the more current ideas is that the lava is actually molten silicate rock. Others say the lava has a lot of sodium. Some spots on Io reach 200 K, but the average of the moon is about 130 K. This is the primary way that Io looses its heat. Io, like our moon, always has the same side facing the planet of Jupiter. Galileo�s recent data says that Io may have its own magnetic field. The surface is made of sulfur dioxide and possibly some other gases. Io also has little to no water, due to the fact that Jupiter was hot enough early in the evolution of the solar system to drive off any and all elements near Io that could bring water. Diameter: 3630 km Mass: 8.93e22 kg Orbit: 422,000 km from Jupiter |