Io
Moon· orbits Jupiter
Io is the innermost Galilean moon and the most volcanically active world in the Solar System, repaved by hundreds of erupting volcanoes powered by tidal heating from Jupiter.
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Key facts
Mass
8.93 × 10²² kg
0.015 M⊕
Radius
1,821 km
1.05× wider than our Moon
Surface gravity
1.8 m/s²
18% of Earth's
Day length
42.31 hours
Orbit around Jupiter
1.76 Earth days
Science
Physical
- Mass
- 8.93 × 10²² kg · 0.015 M⊕
- Radius
- 1,821 km · 1.05× wider than our Moon
- Density
- 3,528 kg/m³ · 3.5× water
- Surface gravity
- 1.8 m/s² · 18% of Earth's
- Escape velocity
- 2.56 km/s · 23% of Earth's
Orbit around Jupiter
- Distance from Jupiter
- 1,404,510 km
- Orbital period
- 42.31 hours
- Eccentricity
- 0.004
- Inclination
- 0.00 °
Rotation
- Rotation period
- 42.31 hours
- Tidal locking
- Tidally locked to its parent
Atmosphere
- Composition
- Tenuous sulfur dioxide (SO₂)
- Surface pressure
- 1.0 × 10⁻4 Pa
Temperature
- Mean
- 110 K (-163 °C)
- Maximum
- 130 K (-143 °C)
Composition
- Bulk composition
- A silicate-rock body with a partly molten interior and an iron core; its surface is coated in sulfur and sulfur-dioxide frosts, continually resurfaced by volcanism.
Radiation & temperature
- Insolation
- 0.0357 S⊕ · 4% of the sunlight Earth receives
- Bond albedo
- 0.52 · reflects 52% of incoming sunlight
- Equilibrium temperature
- 101 K (-172 °C)
- Measured mean temperature
- 110 K (-163 °C)
- Greenhouse warming
- +9 K
Discovery & history
- Discovered
- January 8, 1610
- By
- Galileo Galilei
- Method
- Visual discovery (telescopic)
- Name
- Io, a priestess of Hera loved by Zeus. The name was proposed by Simon Marius in 1614 at Kepler's suggestion, not by the moons' discoverer Galileo, who numbered them instead.
One of the four 'Galilean moons' Galileo found around Jupiter in January 1610. Tidal heating makes Io the most volcanically active body in the Solar System.
Images
Images from open archives · credit shown per image