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a Continuing Story of Discovery


Table of Contents

Overview of Io Facts

Io Quick-Look Statistics

Discovery:                             Jan 7, 1610 by Galileo Galilei
Diameter (km):                              3,630
Mass (kg):                                  8.94x10?22 
Mass (Earth = 1)                            0.014960 
Surface Gravity (Earth = 1):                0.183 
Mean Distance from Jupiter (km):            421,600 
Mean Distance From Jupiter (Rj):            5.905 
Mean Distance from Sun (AU):                5.20 
Orbital period (days):                      1.769138 
Rotational period  (days):                  1.769138 
Density (gm/cm?3)                           3.57 
Orbit Eccentricity:                         0.0041 
Orbit Inclination (degrees):                0.040 
Orbit Speed (km/sec):                       17.34 
Escape velocity (km/sec):                   2.56 
Visual Albedo:                              0.61 
Typical Subsolar Temperature (K)            ~135 
Typical Hotspot Temperature (K)             ~300
Surface Composition:                        Sulphur
A Summary of Facts about Io

Latest Io Science Findings

General/Overview: Volcanic Changes: Atmosphere:

Frequently Asked Questions about Io

Io Images

Galileo Images

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Images from Other Missions
Animations from Non-Galileo Data
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  • Io Rotation Movie
  • Model of the Io Plasma Torus (MPG - 552K)

Missions Exploring Io

Educational Activities and Resources

The Mythology of Jupiter and Its Satellites
The planets and moons in our solar system are all named for characters in Greek and Roman mythology. Here are some stories and artwork about the namesakes of Jupiter and the Galilean satellites.

USGS Io Nomenclature page

The Discovery of the Galilean Satellites
Find out how Galileo Galilei discovered the moons around Jupiter.

Frequently asked Questions (FAQs)


Links to Related Sites