NASA's Juno probe, which arrived in the Jupiter system in 2016, flew over the moon Io on December 30 at an altitude of 1,500 kilometers, which represents the closest approach to the enigmatic star since the beginning of the mission. Juno's visit to Io will provide the best images ever obtained of the moon's surface and will help better understand its extreme volcanism.
At about 3,640 kilometers in diameter, Io is about the same size as Earth's moon. What makes it exceptional is that, with more than 400 active volcanoes, it is the star with the most volcanic activity in the solar system. Its volcanism is attributed to the fact that, of Jupiter's four large moons, it is the closest to the giant planet.
Jupiter's enormous gravity, combined with the tug-of-war caused by the gravity of the other moons, tidally warps Io's crust, causing altitude changes of up to one hundred meters on its surface.
The Juno mission has had as its priority the investigation of Jupiter, rather than that of its moons. Until now the probe has studied Io from afar, approaching distances of between 11,000 and 100,000 kilometers, which has allowed it to observe its north and south poles. Once the main objectives of the mission have been met, NASA has decided to carry out a more detailed study of Io.
“The Juno science team is studying how Io's volcanoes vary,” Scott Bolton, principal investigator of the mission, from the Southwest Research Institute in San Antonio, Texas, said in a statement. "We're looking at how often they erupt, how bright and hot they are, how the shape of the lava flow changes, and how Io's activity is related to the flow of charged particles in Jupiter's magnetosphere."
During the approach, Juno observed Io with its three cameras, NASA reported. The one that detects infrared radiation can identify heat sources in craters and calderas in detail.
Juno will again approach just 1,500 kilometers from Io on February 3. By combining the data from the two approaches, Bolton added, it will be possible to investigate “the origin of Io's massive volcanic activity, whether there is a magma ocean beneath its crust, and the importance of Jupiter's tidal forces, which squeeze relentlessly this tortured moon.”
Although Juno will explore Io in unprecedented detail, it is not the mission that has come closest. The record is held by NASA's Galileo probe, which arrived at Jupiter in 1995 and during the first years did not approach Io for fear that the high radiation so close to Jupiter would damage its instruments, but in 2001 it ventured alone 181 kilometers from the surface of Io.
