One of the final images taken by NASA’s Juno spacecraft in 2023 (on December 30), this shows Jupiter’s moon Io as illuminated by sunlight (right) and Jupitershine (left). Many volcanic features are visible, including, on the lower right, a volcano that juts out above the rest of the spherical horizon, showcasing the height of the mountainous volcanic feature present there. (Credit: NASA / JPL-Caltech / SwRI / MSSS / Björn Jónsson)
NASA’s Juno mission, in orbit around Jupiter, occasionally flies past its innermost large moon: Io. The volcanic activity is unbelievable.
In our Solar System, many planets are volcanically active.
This June 26, 1991 photo of the Mt. Pinatubo eruption in the Philippines shows an enormous volcanic ash cloud towering above the landscape. Although ash clouds are common, the possibility of a high-temperature ash cloud surge is potentially far more deadly and unpredictable. (Credit: TSGT Val Gempis/U.S. National Archives)
Earth, Mars, and Venus all have active volcanoes, driven by internal processes.
These two images of the same region of the surface of Venus, taken by the Magellan spacecraft in 1990 and 1992, show evidence of a changing landscape: consistent with a volcanic eruption resurfacing and adding material to part of the imaged landscape depicted here. The resurfacing, or covering-over of previous craters, is extremely strong evidence for such a phenomenon. Io, however, was the second world in the Solar System (after Earth) that humanity discovered to be volcanically active. (Credit: R.R. Herrick and S. Hensley, Science, 2023)
But the most volcanically active world is Jupiter’s innermost large moon: Io.
When one of Jupiter’s moons passes behind our Solar System’s largest planet, it falls into the planet’s shadow, becoming dark. When sunlight begins striking the moon again, we don’t see it instantly, but many minutes later: the time it takes for light to travel from that particular moon to our eyes. Here, Io re-emerges from behind Jupiter, the same phenomenon that Ole Rømer used to first measure the speed of light, while Europa and Ganymede hover on the right. (Credit: Robert J. Modic)
Io experiences tidal forces ~10,000 times stronger than Earth’s.
When two objects of a finite size gravitationally attract one another, the gravitational force on different parts of the object are different from the average value. This effect causes what we see and experience as tidal forces, which can get extremely large at short distances. Jupiter’s moon Io, with a large physical size but located very close to our Solar System’s most massive planet, Jupiter, experiences the largest tidal forces in the Solar System: some 10,000 times stronger than Earth experiences due to our Moon and Sun combined. (Credit: Krishnavedala/Wikimedia Commons)
This heats and cracks the giant moon, leading to rapid, frequent resurfacing events.
This 1997 Hubble Space Telescope image of Jupiter and its innermost Galilean moon, Io, shows a mound rising from Io’s surface at lower-right: an eruption from the volcano Pillan, which was thought to be dormant before this eruption was spotted. The ejecta consists of sulfur dioxide and moves at speeds of up to 2880 kph (1800 mph). (Credit: NASA/JPL/STScI)
It’s the only known Solar System world without craters: evidence of its surface’s youth.
This image of Jupiter’s innermost Galilean moon, Io, comes courtesy of NASA’s Voyager 1 spacecraft and was taken on March 4, 1979, representing our first close-up view of this volcanically active world. Io is seen from a distance of about 862,000 kilometers (500,000 miles) here, exhibiting both explosive volcanic events that launch enormous plumes into the air as well as lava flowing across the surface from more mundane vents. (Credit: NASA/Voyager 1)
Two spacecraft from the 20th century imaged it up close: Voyager 1 and Galileo.
On July 3, 1999, NASA’s Galileo spacecraft made its closest-ever approach to Jupiter’s moon Io, coming within 130,000 kilometers (80,000 miles) of its surface. A series of images were taken, converted to false color, and tiled together to make this hemispherical mosaic of Io, with North on that world pointing “up” in this view. The resolution of this is 1.3 kilometers (0.8 miles) per picture, and was taking with the Solid State Imaging system. Just 25 years later, Io no longer looks like this in detail, as its rapidly changing surface topography is driven by volcanic activity and near-constant resurfacing. (Credit: NASA/JPL/University Of Arizona)
Those images revealed a pock-marked surface: craterless but littered with volcanoes.
