- Io is the fifth moon in distance from the planet Jupiter.
- It orbits Jupiter at an average
distance of 262,000 miles (422,000 km,) similar to the distance the Moon orbits Earth.
- Io is the third largest of Jupiter's moons and very similar in size to our own moon.
- It is the most volcanically active object in the solar system.
- Volcanic plumes rise almost 190 miles (300 km) above the surface.
- Io has an iron core just like Earth, meaning it could have its own magnetic field.
- The moon's orbit cuts across Jupiter's powerful magnetic field producing 400,000 volts of electricity across its surface.
- Jupiter's magnetic field strips off 1 ton of material from Io every second!
- The moon was discovered in January 1610 by the Italian astronomer Galileo Galilei.
- Io is often compared to a pizza due to its unusual surface which is made up of sulphur dioxide deposits.
Surface, Atmosphere & Temperature
Io's SurfaceJupiter's huge gravity causes Io's surface to bulge up and
down by as much as 100 meters! This also generates tremendous heat inside Io, turning its subsurface into liquid. This molten lava frequently escapes causing its surface to constantly change.
Io's AtmosphereIo's atmosphere is roughly 1 millionth as dense as Earth's atmosphere and made primarily of sulphur.
Io's TemperatureTemperatures on Io vary from extremely hot to extremely cold. Areas which feature volcanic activity can reach temperatures of over 2000C (4000F). Away from these areas however will see temperatures plunge to -143C (-230F).
Io - The volcanic moonThe colorful Jupiter moon Io, the most volcanically active body in the solar system
Volcanic EruptionA giant plume erupting from Io's northern polar Tvashtar volcano
The spectacular surface of Io with volcanic plume
Origin of NameIo is named from Greek mythology after the priestess of Hera who became a lover of Zeus. See Europa for a more detailed explanation.
Life on IoIo is an extremely hostile environment with little or no chance for the existence of life.
Artist impression of Io's surface
Europa Jupiter System MissionLaunch: 2020
A joint venture by NASA and the ESA (Europe) will study Io using two separate spacecraft. Even though they will be focusing mainly on another of Jupiter's moons Europa, they will make four close flybys of Io.
JunoLaunch: August 2011
Arrival: August 2016
Will provide monitoring of Io's volcanic activity using its near-infrared spectrometer.
GalileoLaunch: October 1989
Arrival: December 1995
During its study of the Jovian system Galileo sent back a lot of new data on Io. Including the discovery of several active volcanoes on the moon, the existence of an iron core, and significant changes to the surface since the earlier Voyager missions.
Voyager 1 and 2Launch: August-September 1977
Arrival: April-August 1979
As part of its "Grand Tour" of the solar system Voyager 1 and 2 took high resolution images of Io revealing an oddly multi colored moon with a curiously craterless surface. After the images were sent back to Earth a young female engineer noticed a plume emanating from the surface on one of the pictures proving that Io was volcanically active.
Pioneer 10 and 11Launch: March 1972 - April 1973
Arrival: December 1973 - December 1974
The first spacecrafts to explore the outer solar system. They provided little data on Io apart from a better estimate of its mass. Pioneer 11 managed to take only one image of any quality pictured left.