Jupiter's Moon Io
Written by Fraser Cain
If you start at Jupiter and then move outward, Io is the moon orbiting closest. It has a diameter of 3,642 kilometers, and it's the 4th largest moon in the Solar System.
The most dramatic features of Io are its 400 active volcanoes; Io is the most volcanically active body in the Solar System. Since Io orbits Jupiter so closely, the planet's intense gravitational field flexes the moon's interior. Even thought the moon should have cooled down long ago, this tidal flexing keeps its interior very hot.
The volcanic plumes on the surface of Io can spray sulfur and sulfur dioxide 500 km above the surface of the moon. As the material rains back down, it creates huge circular bruises across the surface of Io that can be colored various shades of red, yellow, white and even black.
Io was first discovered by Galileo Galileo when he turned his first 33-power rudimentary telescope on Jupiter. Galileo spotted the 4 large moons orbiting Jupiter, and realized that not everything in the Solar System orbits the Earth.
Io plays a role in shaping Jupiter's magnetic field. The planet's magnetosphere is drawing material away from Io's thin atmosphere at a rate of 1 tonne per second. This material ends up in clouds around Jupiter, and eventually escapes into space.
This innermost moon of Jupiter shares some other properties of planets, including a thin atmosphere of sulfur dioxide and mountains; some as large as 17 km tall.
The moon Io got its name from Greek mythology. Io, the person, was a priestess of Hera who became one of Zeus' many lovers.
We have written many stories about Io here on Universe Today, including this one about Galileo's last visit to Io, and how hot Io can get.
Here's NASA's Solar System Explorer information on Io, and this great picture from Astronomy Picture of the Day of Io hovering over the surface of Jupiter.
We've also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter's Moons.
Filed under: Astronomy
