Io: The Moon That Has More Volcanos Than Earth

Jupiter’s moon Io is the most volcanically active body in the Solar System. Its slightly larger than our own Moon and over 150 volcanos have been discovered on it, some of which shoot material 300 kilometres into space. At a distance of 422,000 kilometres, Io orbits extremely close to Jupiter and the two are locked in an endless gravitational tug of war. The great planet’s pull heats up Io’s interior to incredible temperatures. As a result, the moon itself is 4.5 billion years old but its surface is constantly changing due to all the activity and is very young, possibly only two million years. Where the Earth and the Moon’s interaction causes the oceans to rise and fall by 18 metres, Jupiter is responsible for stretching and squeezing Io’s rocky surface by as much as 100 metres. Io was the first time we discovered volcanism somewhere other than our own planet.

Io was one of four moons (the others being Europa, Ganymede and Callisto) discovered by Galileo Galilei when he pointed a telescope at Jupiter on January 8, 1610. Galileo observed them for some time and concluded that they were actually orbiting Jupiter itself. It was the first time we learnt that the universe didn’t revolve around the Earth.

The two Voyager space probes left Earth in 1977 and their missions were to explore the outer planets—Jupiter, Saturn, Uranus and Neptune. There was little interest in the moons of these worlds because scientists expected them to be like our own Moon: dead, cold and covered in impact craters. If it wasn’t for the efforts of planetary scientist Bruce Murray pushing for the outer moons to be included as targets, their uniqueness and wonders could still remain unknown today.

On March 5, 1979, Voyager 1 got as close to Jupiter as it would get during its flyby. It took detailed photos and collected data that was transmitted back to Earth via radio signals.

Linda Morabito was part of the Voyager navigational team. Her job was to use images of the stars, Jupiter and its moons to determine Voyager 1’s position in space and where it was heading. Because each Voyager probe was travelling at over 61,000 kilometres per hour, information needed to be as precise as possible because upcoming course corrections needed to be known down to the split second so the spacecraft could angle itself correctly and take pictures.

The first images of Io were coming in and one caught Morabito’s attention. A plume of something was coming from the moon’s surface and she didn’t know what it was. She thought it was possibly a photo blemish. She spoke with colleagues in the other teams to get their input. Each possible theory was debunked one by one, including the photo issue, until only a final remained: the plume was coming from Io itself. Morabito had witnessed the first ever active volcano outside of the Earth. Her discovery was announced at a NASA press conference a short time later.

The moons of Saturn, Uranus and Neptune became priorities after Voyager 1’s encounter with Jupiter. Voyager 2 flew past Io four months later confirming more volcanos and that some previously discovered were still erupting.

Jupiter was visited again by the Galileo spacecraft. Unlike the two Voyagers that were flybys only, Galileo entered orbit into the Jupiter system and studied the planet and its moons in greater detail between 1995 and 2003.

A similar probe to Galileo, Juno, has been in the Jupiter system since 2016 and is building upon the knowledge learnt from the Voyager and Galileo missions.

Photo Credit: NASA


Galileo (

Io (

Io: Facts about Jupiter’s Volcanic Moon (

Juno (

Jupiter’s Hot, Mushy Moon (

Linda Morabito (

The Planets (1999 TV Mini-Series)

Space Topics: Voyager The Stories Behind the Mission: Linda Morabito Kelly (

This is our best look yet at the solar system’s most volcanic object (

Volcanoes on Io: an interview with Voyager scientist Linda Morabito (

Voyager 1 (

Voyager 2 (

Leave a Reply

Up ↑

%d bloggers like this: