Nasa’s Juno spacecraft has received one of the most explicit images of Jupiter’s moon, Io, showcasing the tortured surface of the most volcanic world in our Solar System. The new photos showcase Io’s lava-scarred surface in unprecedented detail and reveal that much of the moon is still active, with volcanoes constantly spewing tons of molten lava.
Despite its small size, it is one of 92 moons that orbit Jupiter and the fifth largest in the Solar System. It is the most volcanically active body in our Solar System, with hundreds of erupting hot spots and a total area of nearly 2,000 square miles (4,400 kilometers).
The new image was taken by JunoCam, a powerful imaging system aboard the spacecraft, as it passed by Io on October 15, 2023. Juno’s flyby was the first of three to occur during the mission’s third orbit of Jupiter, and the close pass allowed Juno to gather detailed data on Io’s volcanic activity, including its temperature.
According to NASA, planetary scientists can use these observations to study the relationship between patterns of volcanism and Io’s interior. The images also allow them to monitor the evolution of Io’s neutral cloud, produced by vaporous sulfur dioxide. The neutral clouds often change color and sometimes contain salts like sodium chloride or potassium chloride. These changes can indicate that a volcanic eruption is occurring.
As part of the observation, a team led by Rosaly Lopes of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, studied the light curves of Io’s hot spots. The resulting data shows that regions that look bright in visible light appear dark in ultraviolet light because sulfur dioxide absorbs UV radiation. This demonstrates that the brightness of Io’s volcanoes is primarily due to the size of the sulfur dioxide particles.
Another important finding was that Io’s thermal structure is more complicated than previously thought. The study showed that a persistent hot spot called Kanehekili erupted on May 8, 2015, generating a thermal plume that extends at least 300 miles from the site. This plume is associated with a large Y-shaped black patch on Io, observed by the Voyager and Galileo missions in the 1990s/2000s and ground-based telescopes in recent years.
A streak on the edge of Io called Loki Patera was also an indicator of an ongoing eruption. On May 16, the infrared camera, JIRAM, spotted a smudge near Loki, which looked like an active volcano based on its brightness and temperature. JIRAM was able to pinpoint the location of this hot spot using information about the onset and duration of the eruption from other observations.
These results help confirm a model that predicts that Io’s volcanoes form and grow where tidal heating from Jupiter and sibling moons Europa and Ganymede occurs. The team’s next steps will be to investigate Io’s thermal properties at finer spatial resolutions. The JPL team is pushing for a dedicated spacecraft, referred to in early proposals as the Io Volcano Observer (IVO), which would zoom within 1,500 miles of Io on each flyby.
