Io Moon Facts
Io Facts
  • 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 Surface
Jupiter'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 Atmosphere
Io's atmosphere is roughly 1 millionth as dense as Earth's atmosphere and made primarily of sulphur.
Io's Temperature
Temperatures 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 moon
jupiter moon io The colorful Jupiter moon Io, the most volcanically active body in the solar system

Volcanic Eruption
volcanic eruption A giant plume erupting from Io's northern polar Tvashtar volcano
Io Origin of Name and Life
surface of io
The spectacular surface of Io with volcanic plume

Origin of Name
Io 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 Io
Io is an extremely hostile environment with little or no chance for the existence of life.

Io - The Volcanic Moon
io eruption
As Voyager 1 and 2 approached the Jupiter system in the late 1970's NASA scientists fully expected the craft to discover that its moons would be cold, dead and not particularly interesting, instead what they found was quite astonishing. One moon in particular stood out, Io, scientists were amazed to find out that it was in fact geologically active with volcanoes constantly erupting on its surface. The sulphur deposits from the eruptions also made the small moon strikingly colorful.

Scientists initially scratched their heads and wondered how a small moon in one of the coldest parts of the solar system could be generating so much heat. The explanation was in fact very simple, Io's orbit around Jupiter is extremely elliptical, meaning that sometimes it's close to the giant planet and other times it's further away. This causes Jupiter’s strong gravity to push and pull the small moon, producing immense heat inside Io and creating molten lava below its surface.

Scientists had expected to find something similar to our moon but what they had in fact discovered was the most geologically active body in the entire solar system.

Images & Video
Volcanic plume
Volcanic plume io
Io Rotation
Artist impression of Io's surface
Artist impression of Io's surface
Future and Past Missions to Io
Europa Jupiter System Mission
Europa Jupiter System Mission Launch: 2020
Agency: NASA/ESA
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.
Juno
juno Launch: August 2011
Arrival: August 2016
Agency: NASA
Will provide monitoring of Io's volcanic activity using its near-infrared spectrometer.
New Horizons
new horizons Launch: January 2006
Arrival: January 2007
Agency: NASA
During its flyby of the Jovain system New Horizons captured several spectacular images of Io including the eruption of its north polar volcano.

Galileo
galileo Launch: October 1989
Arrival: December 1995
Agency: NASA
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 2
Voyager 2 Launch: August-September 1977
Arrival: April-August 1979
Agency: NASA
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 11
image of Io taken by Pioneer 10 Launch: March 1972 - April 1973
Arrival: December 1973 - December 1974
Agency: NASA
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.

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