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Solar system
Jupiter's moon, Io

4.5 billion years, about the same age as Jupiter


Solar system, in orbit around Jupiter

Avg. distance from Jupiter

421,700 km (262,000 mi)


3,642 km (2,263 mi)


8.9319 x 1022 kg

Orbital period around Jupiter

1.77 days. The same side of Io always faces Jupiter. It takes the same amount of time to make one revolution on its axis as it does to complete an orbit around Jupiter.

Distinguishing features

Io, the innermost of the four Galilean moons, is the most geologically active object in the solar system. With more than 400 volcanoes, Io's mottled surface is constantly changing, painted in shades of red, yellow, white, black, and green. Unlike most solar system moons, which are composed of water ice, Io is mostly rock with an iron core.

Jupiter's moon, Io

Enlarge Image


"Fast Facts: Jupiter's moon, Io" is a table that lists the moon's age, location, average distance from Jupiter, diameter, orbital period around Jupiter, mass, and distinguishing features. A picture of Io is included.

Printer-friendly web page
Adaptable, at teacher's discretion
How to use in the classroom

Use this resource as:

A source of information. Read the table to find out about this object.

A large-number recognition and ordering activity. Have students review several Fast Fact moon tables, including this one. Have students read the tables to find each object's mass. Then ask them to arrange the objects according to their mass, from smallest to largest. Students also can arrange the objects according to their diameter.

A math activity. Use Newton's law of gravitation, the distance between Io and Jupiter, and the masses of the two objects to determine the gravitational force between them. (Recommended for grades 10-12)

An inquiry tool. Have students write down questions they would like answered about the image and the information in the Fast Facts table.

An engagement tool. Involve students in a discussion.

Related materials

Amazing Space resources by topic: Solar system

HubbleSite: Press releases on Moons