Io

Table of Contents

Introduction References & Edit History Related Topics

Images & Videos

Learn about Io, Jupiter's moon with the most active volcanoes in the solar system

global mosaic of Jupiter's moon Io

Io's Tvashtar volcano

volcanic plumes on Io

Io, in Jupiter's shadow, photographed by the Galileo spacecraft on May 6, 1997. The relative brightnesses of Io's features are enhanced with added colour, red being the most intense, yellow-green moderate, and blue the faintest. Small red and yellow-green spots are probably lava flows or lakes, while the bright area extending from Io's left limb corresponds to the plume from the volcano Prometheus. The diffuse glow on the right limb also has plumelike characteristics.

Jupiter's four Galilean moons

Io, moon of Jupiter. A massive volcano can be seen on the horizon.

Jupiter's atmospheric blemishes

Read Next

Colorful winter sunset

What's the Difference Between a Solstice and an Equinox?

Planet Jupiter with its moon Io at left, photographed by the Cassini orbiter during the Cassini-Huygens mission, 2000. spacecraft

7 Important Dates in Jupiter History

Pluto. The Changing Faces of Pluto. Most detailed view to date of the entire surface of the dwarf planet Pluto, as constructed from multiple NASA Hubble Space Telescope photographs taken from 2002 to 2003.

10 Important Dates in Pluto History

Solar system illustration. (planets; sun)

Why Are Planets Round?

Galaxy clusters like Abell 2744 can act as a natural cosmic lens, magnifying light from more distant, background objects through gravity. NASA's James Webb Space Telescope may be able to detect light from the first stars in the universe if they are gravitationally lensed by such clusters. (astronomy, space exploration, galaxies)

How Fast Is the Universe Expanding?

Discover

The Colosseum, Rome, Italy. Giant amphitheatre built in Rome under the Flavian emperors. (ancient architecture; architectural ruins)

New Seven Wonders of the World

Candles Burning On Table In Church

What Is the Most Widely Practiced Religion in the World?

Illustration for Demystified "How Dangerous is Quicksand"

How Deadly Is Quicksand?

Ice Sledge Hockey, Hockey Canada Cup, USA (left) vs Canada, 2009. UBC Thunderbird Arena, Vancouver, BC, competition site for Olympic ice hockey and Paralympic ice sledge hockey. Vancouver 2010 Olympic and Paralympic Winter Games, Vancouver Olympics

10 Best Hockey Players of All Time

Agnes with a lamb near her feet. St. Agnes (Saint Agnes) design drawing for stained glass window by J&R Lamb Studios, ink, mount size 10.5 x 14.5 in.

Roman Catholic Saints

July, 2006, Launch of Space Shuttle Discovery STS-121. See attached for full caption information.

Will Light-Speed Space Travel Ever Be Possible?

Figure 13: A Maxim machine gun, belt-fed and water-cooled, operated by German infantrymen, World War I.

7 Deadliest Weapons in History

Io: Related Content

Written and fact-checked by The Information Architects of Encyclopaedia Britannica

News •

NASA finds 'glass-smooth lake of cooling lava' on Jupiter's moon Io • Apr. 5, 2025, 6:17 AM ET (Earth.com)

Photos and Videos

global mosaic of Jupiter's moon Io

Io's Tvashtar volcano

volcanic plumes on Io

Io, in Jupiter's shadow, photographed by the Galileo spacecraft on May 6, 1997. The relative brightnesses of Io's features are enhanced with added colour, red being the most intense, yellow-green moderate, and blue the faintest. Small red and yellow-green spots are probably lava flows or lakes, while the bright area extending from Io's left limb corresponds to the plume from the volcano Prometheus. The diffuse glow on the right limb also has plumelike characteristics.

Jupiter's four Galilean moons

Io, moon of Jupiter. A massive volcano can be seen on the horizon.

Jupiter's atmospheric blemishes

volcanic eruption on Io

Learn about Io, Jupiter's moon with the most active volcanoes in the solar system

See All Videos and Images →

Topics

Moon Titan Europa Ganymede Enceladus Phobos Triton Callisto Charon Deimos

Dig Deeper: More Articles That Discuss This Topic

Jupiter: Io

Quiz

Nicolaus Copernicus. Nicolas Copernicus (1473-1543) Polish astronomer. In 1543 he published, forward proof of a Heliocentric (sun centered) universe. Coloured stipple engraving published London 1802. De revolutionibus orbium coelestium libri vi.

All About Astronomy

Saturn. Saturn and its rings. Second largest planet of the solar system. Space Art

Planets and the Earth’s Moon

The orbits of the planets and other elements of the solar system, including asteroids, Kuiper belt, Oort cloud, comet

Space Odyssey

View of the Andromeda Galaxy (Messier 31, M31).

Astronomy and Space Quiz

Demystified

Colorful winter sunset

What's the Difference Between a Solstice and an Equinox?