In a close encounter of the Jovian kind, NASA’s Juno deep space probe has made its closest flyby yet of Jupiter’s volatile moon I
o. During its 51st orbit of the giant planet, the solar-powered robotic spacecraft came within 22,600 miles (35,500 km) of Io’s volcanic surface.
First launched from what is now Cape Canaveral Space Force Station in Florida atop an Atlas V rocket on August 5, 2011 on the start of a seven-year mission, Juno is now well into its 12th year. On July 5, 2016, it went into orbit around Jupiter and has, to date, traveled over 510 million miles (820 million km).
Despite this, Juno has only completed 50 orbits of Jupiter. This is because its trajectory takes it far away from the planet in very long arcs that take weeks at a time. This gives the spacecraft the ability to observe Jupiter and its moons from different vantage points and minimizes the damage to the craft’s systems from passing through Jupiter’s deadly radiation belts.
During the latest flyby, NASA scientists were keen to collect new data – both to help plan future missions and to learn more about the most volcanically active body in the solar system. Even though it’s smaller than the Earth’s Moon, Io has a molten interior and sulfur-spewing volcanoes that erupt with frightening regularity. This is because it orbits close to Jupiter and the tidal forces of the giant planet keep pulling at Io, pumping energy into its geology.
During the encounter on May 15, 2023, Juno not only collected pictures with its JunoCam, but also took readings with its Jovian InfraRed Auroral Mapper (JIRAM), Stellar Reference Unit (SRU), and Microwave Radiometer (MWR) to observe the moon’s volcanoes and magnetosphere.
“Io is the most volcanic celestial body that we know of in our solar system,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. “By observing it over time on multiple passes, we can watch how the volcanoes vary – how often they erupt, how bright and hot they are, whether they are linked to a group or solo, and if the shape of the lava flow changes.
“We are entering into another amazing part of Juno’s mission as we get closer and closer to Io with successive orbits. This 51st orbit will provide our closest look yet at this tortured moon. Our upcoming flybys in July and October will bring us even closer, leading up to our twin flyby encounters with Io in December of this year and February of next year, when we fly within 1,500 kilometers (930 miles) of its surface. All of these flybys are providing spectacular views of the volcanic activity of this amazing moon. The data should be amazing.”