The fifth planet from the sun, Jupiter is over 300 times more massive than Earth and over twice as massive as every other planet in the solar system combined. NASA first sent a probe there in 1973, when Pioneer 10 obtained close-up images and took measurements of its massive magnetic field and radiation belts. Several more spacecraft followed, including Voyager 1 and Voyager 2 in 1979, as well as Galileo, which circled the giant ball of gas from 1995 to 2003. Yet much about it remains unknown. Scientists suspect but haven’t proven, for instance, that Jupiter contains a rocky inner core.
Enter Juno, a spinning, solar-powered spacecraft the length of a basketball court, which launched from Cape Canaveral, Florida, in August 2011. Named for the wife of Jupiter in Roman mythology, who could see through the veil of clouds he created to hide his transgressions, it has since traveled nearly 1.8 billion miles, finally reaching its destination yesterday after an engine burn slowed it down enough for Jupiter’s gravity to grab hold. (Had the burn failed, Juno would have flown right past the planet and back into outer space.) “We are looking great,” Scott Bolton, Juno’s principal investigator, said today in a statement. “It’s a great day.”
Now, if all continues according to plan, Juno will complete 37 elliptical polar orbits over the next 20 months, at times coming within about 3,100 miles of Jupiter’s cloud tops—closer than NASA has ever gotten before. “We could not be more excited about being back on Jupiter’s doorstep,” Diane Brown, Juno’s program executive, said at a recent press conference, adding that the $1.13 billion mission “is poised to answer the questions we still have” about the planet.
With assistance from the Hubble Space Telescope and several earthbound observatories, Juno will take a particular interest in Jupiter’s auroras, which are hundreds of times more energetic than our auroras, or polar lights. It likewise hopes to find out how Jupiter’s magnetic field is produced, whether the highly pressurized core is indeed rocky, how much nitrogen and oxygen the atmosphere contains, and whether the Great Red Spot—a storm bigger than Earth that has been raging for centuries—is merely an atmospheric phenomenon or something deeper.
All this will be done, NASA says, with an eye toward extrapolating about Jupiter’s origin. Scientists believe the gas giant took shape before the other planets in the solar system, nabbing most of the cosmic material leftover following the creation of the sun. However, they don’t know whether the core came first and then gravitationally captured huge amounts of hydrogen and helium—by far the two most common elements on Jupiter—or whether an unstable cloud of gas and dust collapsed inward, which is how the sun supposedly formed. Another debate centers on whether Jupiter migrated around the solar system in its youth. “[We] don’t really understand how the planets are made,” said Bolton, adding that this important “first step eventually leads to us.”
In addition to several science instruments, including a microwave radiometer and an ultraviolet imaging spectrograph, Juno is carrying a camera that will snap the first-ever close-up images of Jupiter’s poles. As part of NASA’s public-outreach campaign, people can vote on exactly where to aim it. “We want to invite everyone along for the ride,” Bolton said. To engage children, the spacecraft also has three 1.5-inch Lego figurines onboard: one of Jupiter, king of the Roman gods; one of his goddess wife, Juno; and one of the astronomer Galileo Galilei, who discovered Jupiter’s four largest moons in 1610.
Though a titanium vault shields most of Juno’s science instruments, radiation will purportedly zap the spacecraft with the equivalent of more than 100 million dental X-rays and eventually render them useless. “Jupiter is basically the harshest region in the entire solar system,” Bolton said. “It is a planet on steroids. Everything about it is extreme.” As a result, the mission is scheduled to end in February 2018, when Juno will plunge into Jupiter’s atmosphere and burn up like a meteor. NASA next plans on visiting Jupiter in the late 2020s to investigate whether its moon Europa could possibly support life.