At 11.53 p.m. EDT on 4 July, NASA controllers received confirmation that their latest planetary probe, Juno, had arrived safely at Jupiter. With three simple tones the probe, which was in a form of safe mode during a 35-minute engine burn, signaled that it had successfully slowed its speed and entered into orbit around the solar system’s biggest planet. Diane Brown, Juno program executive at NASA headquarters in Washington, D.C., told reporters at a postinsertion briefing that after the spacecraft’s 5-year journey, the feeling was “overwhelming” and the orbital insertion was “flawless.” She added: “Being able to go to bed knowing we don’t have to worry about what will happen tomorrow is pretty awesome.”
Juno will peer through Jupiter’s outer veil of clouds to study its structure deep into the interior. It will swoop down closer to Jupiter than any spacecraft has gone before, just 4000 kilometers above the cloud tops. The aim is to study the giant planet’s origin and evolution: How far down do the surface stripes and swirling storms go? How do structures deep inside the planet affect what we see on the surface? What is the source of Jupiter’s intense magnetic field? And does it have a solid rocky core?
Theorists believe that, as the solar system’s largest resident, Jupiter holds the key to understanding how the whole body of planets formed around the protostar that became our sun. “A question I’ve had my whole life is, how did we get here? That’s been pretty fundamental to me,” says Juno principal investigator Scott Bolton of the Southwest Research Institute in San Antonio, Texas. “Now the fun begins—the science.”
The team of controllers is now powering up the craft’s systems after the insertion burn, the highest risk part of the mission, and downloading data about its health. Science instruments will be turned on 5 days from now. The first full set of observations will begin at the end of August after the initial 53-day orbit. The craft will then settle into a 14-day orbit and circle the planet pole-to-pole 33 times over the next year and a half before being plunged into Jupiter’s clouds at the end of its mission to prevent an accidental collision with one of Jupiter’s moons, which could contaminate them with earthly microbes.