The Galileo spacecraft arrived at Jupiter in 1995 after a six-year journey from Earth to follow up on the discoveries of the two Voyager probes and ground-based observations taken in the intervening years.
Io's location within one of Jupiter's most intense radiation belts precluded a prolonged close flyby, but Galileo did pass close by shortly before entering orbit for its two-year, primary mission studying the Jovian system.
Although no images were taken during the close flyby on 7 December 1995, the encounter did yield significant results, such as the discovery of a large iron core, similar to that found in the rocky planets of the inner Solar System.

Despite the lack of close-up imaging and mechanical problems that greatly restricted the amount of data returned, several significant discoveries were made during Galileo's primary mission.
Galileo observed the effects of a major eruption at Pillan Patera and confirmed that volcanic eruptions are composed of silicate magmas with magnesium-rich mafic and ultramafic compositions.
Distant imaging of Io was acquired for almost every orbit during the primary mission, revealing large numbers of active volcanoes (both thermal emission from cooling magma on the surface and volcanic plumes), numerous mountains with widely varying morphologies, and several surface changes that had taken place both between the Voyager and Galileo eras and between Galileo orbits.

The Galileo mission was twice extended, in 1997 and 2000.
During these extended missions, the probe flew by Io three times in late 1999 and early 2000 and three times in late 2001 and early 2002.
Observations during these encounters revealed the geologic processes occurring at Io's volcanoes and mountains, excluded the presence of a magnetic field, and demonstrated the extent of volcanic activity.
In December 2000, the Cassini spacecraft had a distant and brief encounter with the Jovian system en route to Saturn, allowing for joint observations with Galileo.
These observations revealed a new plume at Tvashtar Paterae and provided insights into Io's aurorae.
The Galileo spacecraft arrived at Jupiter in 1995 after a six-year journey from Earth to follow up on the discoveries of the two Voyager probes and ground-based observations taken in the intervening years. Io's location within one of Jupiter's most intense radiation belts precluded a prolonged close flyby, but Galileo did pass close by shortly before entering orbit for its two-year, primary mission studying the Jovian system. Although no images were taken during the close flyby on 7 December 1995, the encounter did yield significant results, such as the discovery of a large iron core, similar to that found in the rocky planets of the inner Solar System.
Despite the lack of close-up imaging and mechanical problems that greatly restricted the amount of data returned, several significant discoveries were made during Galileo's primary mission. Galileo observed the effects of a major eruption at Pillan Patera and confirmed that volcanic eruptions are composed of silicate magmas with magnesium-rich mafic and ultramafic compositions. Distant imaging of Io was acquired for almost every orbit during the primary mission, revealing large numbers of active volcanoes (both thermal emission from cooling magma on the surface and volcanic plumes), numerous mountains with widely varying morphologies, and several surface changes that had taken place both between the Voyager and Galileo eras and between Galileo orbits.
The Galileo mission was twice extended, in 1997 and 2000. During these extended missions, the probe flew by Io three times in late 1999 and early 2000 and three times in late 2001 and early 2002. Observations during these encounters revealed the geologic processes occurring at Io's volcanoes and mountains, excluded the presence of a magnetic field, and demonstrated the extent of volcanic activity. In December 2000, the Cassini spacecraft had a distant and brief encounter with the Jovian system en route to Saturn, allowing for joint observations with Galileo. These observations revealed a new plume at Tvashtar Paterae and provided insights into Io's aurorae.
Io (moon)