July 4, 2016

— For only the second time in space history, a probe is now orbiting Jupiter, looping from pole to pole to improve our understanding of the formation and evolution of the largest planet in the solar system.

NASA's Juno spacecraft, a solar-powered probe about the size of a basketball court, survived a 5-year, 1,740-million-mile (2,800-million-km) journey from Earth to arrive in polar orbit around the Jovian world on Monday night (July 4).

Accelerated by Jupiter's gravity to a record-setting speed of about 165,000 mph (265,000 km/h) relative to the Earth, Juno fired its main engine at 10:30 p.m. EDT (0230 GMT; 11:18 p.m. EDT Earth receive time) for 35 minutes to slow its approach such that it did not sail right past the giant gas planet.

"We're in it!" exclaimed principal investigator Scott Bolton, of the Southwest Research Institute, reacting to the signal confirmation that Juno had entered orbit. "We just did the hardest thing NASA's ever done. That's my claim."

"So we're there, we are in orbit, we conquered Jupiter," he added at press conference following the insertion.

Click to enlarge and view video in new pop-up window. (NASA)

Now in the first of its planned 37 trips around Jupiter, the danger to Juno has just begun. From its unique polar orbit, the spacecraft will repeatedly dive between the planet and its intense radiation belts, coming as close as 2,600 miles (4,100 km) to the top of Jupiter's clouds at its closest pass.

"Jupiter is extreme in every way," said Bolton. "It has the strongest magnetic field, it's spinning the fastest, it has the strongest gravity field, it has the most intense radiation and we're flying the fastest of any spacecraft — carrying these giant solar arrays, spinning."

"That all sounds okay... but I also look at it and I am like, 'What were we thinking?'" Bolton said.

Juno is designed though, unlike any spacecraft before it, to survive its mission around Jupiter.

To protect its electronics, Juno is outfitted with a first-of-its-kind shielded vault, a critical feature for enabling sustained exploration in such an intense radiation environment. The vault, which is about the size of an SUV's trunk, encloses Juno's command and data handling box (the spacecraft's brain), power and data distribution unit (its heart) and 20 other electronic assemblies.

To power the spacecraft and its nine on board instruments (eight science instruments and a color camera, JunoCam, for education and public outreach), Juno is equipped with three solar array wings, the largest ever to be deployed on a planetary probe. The 30-foot-long (9-m.) arrays are each outfitted with 18,698 electricity-generating cells, enabling Juno to become the farthest solar-powered craft to voyage away from Earth.

Juno's first two revolutions around Jupiter will be 53.5 days long, during which time its instruments will be turned back on and calibrated. Then, on Oct. 19, Juno will maneuver into its science orbit, looping around the outer planet every 14 days.

NASA's Juno spacecraft, seen prior to launch in 2011, is about the size of a basketball court with its solar arrays deployed (NASA)

As a result of its highly elliptical path, at each perijove — its closest approach to Jupiter — Juno will travel from pole to pole in just two hours time. As Jupiter rotates beneath the spacecraft, the planet's entire surface will covered by Juno's suite of science instruments.

The first mission to orbit Jupiter, NASA's Galileo, dropped a probe into the atmosphere in 1995, sending back data that showed that Jupiter's composition was different than scientists thought, indicating that their theories of planetary formation were wrong. The primary goal of Juno's mission is to provide answers to the many questions that Galileo's data raised.

Juno will observe the planet's gravity and magnetic fields, atmospheric dynamics and composition, and the coupling between the interior, atmosphere and magnetosphere that determines the planet's properties and drives its evolution. It will investigate the existence of a possible solid planetary core, measure the amounts of water and ammonia within the deep atmosphere and observe the planet's auroras.

The data Juno returns will represent a giant step forward in our understanding of how giant planets form and the role they played in putting together the rest of the solar system.

Artist rendering showing NASA's Juno spacecraft above the north pole of Jupiter. (NASA/JPL-Caltech)

"We are going to get the answers we are all seeking about the beginning of our solar system," said Bolton.

By its 37th orbit, a de-orbit burn will be executed, placing Juno on a path that will lower its perijove to an altitude that is below Jupiter's cloud tops on Feb. 20, 2018. The craft was not designed to operate in Jupiter's atmosphere and will burn up.

Launched on Aug. 5, 2011, Juno will have traveled a total distance of 2,106 million miles (3,390 million km) when it impacts Jupiter. During just the time it is in orbit around the planet, the craft will travel 15 times farther than the closest distance between Earth and Jupiter.

Although the second mission to orbit Jupiter after Galileo, Juno is ninth spacecraft in history to visit the giant planet. NASA's Pioneers 10 and 11, Voyagers 1 and 2, Ulysses, Cassini and New Horizons probes flew by Jupiter as part of their science objectives or to benefit from the planet's gravity on their way to their respective destinations.