Next June, the solar-powered spacecraft will take off Ganymede, the largest moon in the solar system. Then in 2022, Will visit EuropeAn ocean world covered in ice can support life. Finally, when Juno boldly approaches Jupiter, you will meet Io, a volcanic moon covered in sulfur frost. Seeing these moons up close for the first time in nearly two decades, since the Galileo spacecraft mission ended in 2003, will excite scientists studying the elusive icy worlds of the outer solar system.
“I’m still trying to channel this hashtag: #PlanetsAreOverrated,” says Julie Rathbun of the Institute of Planetary Science, who studies Io. “Satellites and satellites are more interesting.”
In addition to studying those three moons, Juno will also carefully examine the rings of Jupiter, and make several passes through the bracelets. The dark, mysterious rings aren’t as amazing as those of Saturn, and scientists know very little about them.
“It’s very rare that there is a mission in the outer solar system, and it’s amazing that we can take advantage of this existing spacecraft,” says Cynthia Phillips of the Jet Propulsion Laboratory, which studies icy moons of the outer solar system. “It’s basically a brand new mission.”
Half a decade on Jupiter
Juno was launched in 2011 and entered orbit around Jupiter on July 4, 2016. The spacecraft’s primary goals included studying gravity, magnetic fields, the atmosphere, and the interior of the gas giant.
But Juno, named after the goddess’s wife, Jupiter, is perhaps best known for her remarkable portraits of the greatest scientist in the solar system. For centuries, we have watched from afar how huge storms swept across the face of the planet. But up close, through the lens of JunoCam, Jupiter is an water-colored world punctuated by numerous whirling tornadoes that gather near their never-before-seen poles.
In addition to its thin-ring system, the planet orbits 79 moons, including 12 that were discovered by chance just three years ago. The four largest moons, known as the Galileo moons, were first discovered in the early 17th century by the Italian astronomer Galileo Galilei, who initially thought they were stars. Now Ganymede, Callisto, Europa and Io are among the most interesting places in the Solar System, although few spacecraft have come close enough to study them in detail. The Voyager spacecraft flew in 1979 and the Galileo spacecraft scanned Jupiter’s system for eight years starting in 1995.
“I still am amazed by the paucity of the information we have on all of these moons of Galilee,” says Rathbone.