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NASA’s Juno Spacecraft Enters Jupiter’s Orbit

It took five years for Juno to travel this far on its $1.1 billion mission, and the moment was one that NASA scientists and space enthusiasts had eagerly — and anxiously — anticipated.

At 11:53 p.m., Eastern time, a signal from the spacecraft announced the end of a 35-minute engine burn that left it in the grip of its desired orbit around Jupiter. Cheers and clapping erupted at the mission operations center at NASA’s Jet Propulsion Laboratory, in Pasadena, Calif., which is managing Juno.

“This is the hardest thing NASA has ever done,” Scott Bolton, Juno’s principal investigator, told the mission team a few minutes later. “That’s my claim.”

Status messages for each maneuver of the spacecraft came in as expected. The length of the engine firing turned out to be within one second of what had been predicted.

Diane Brown, the program executive for Juno at NASA headquarters, described the performance as flawless.

“To know we can all go to bed tonight, not worrying about what’s going to happen tomorrow, it’s pretty awesome,” she said at a news conference.

Rick Nybakken, Juno’s project manager, held up a sheaf of papers as he celebrated the smooth execution of the maneuver.

“We prepared a contingency communications procedure, and guess what?” he said, ripping the papers. “We don’t need that anymore.”

Juno is just the second spacecraft to enter orbit around Jupiter. NASA’sGalileo spacecraft spent eight years there surveying the planet and its many moons. But except for a probe that parachuted into Jupiter’s atmosphere, Galileo did not have the tools that Juno does to delve into what lies beneath Jupiter’s clouds.

“We have a chance with Juno to go back and study the planet in its own right,” James L. Green, the director of planetary science at NASA, said during a news conference earlier on Monday.

Jupiter, most likely the first planet formed after the sun, is believed to hold the keys to understanding the origins of our solar system. How much water it contains and the possible presence of a rocky core could reveal where in the solar system Jupiter was created and provide clues to the early days of other planets.

Juno’s instruments are designed to precisely measure the magnetic and gravitational fields of Jupiter and the glow of microwaves emanating from within. That, for instance, will give hints about storm systems like the visible Great Red Spot, which has persisted for centuries, although it has been shrinking.

“Juno is really searching for some hints about our beginnings, how everything started,” Dr. Bolton said. “But these secrets are pretty well guarded by Jupiter.”

Dr. Bolton repeatedly described Jupiter as “a planet on steroids” in discussing the unprecedented dangers Juno faced Monday night.

Ensnared by Jupiter’s gravity, Juno accelerated quickly to its rendezvous with the planet, passing within the orbit of Callisto and Ganymede, two of the main moons, on Sunday. It zoomed past the other two, Europa and Io, on Monday.

Juno’s Approach to Jupiter Video by NASA Jet Propulsion Laboratory

Juno has been on its own since Thursday, performing a programmed sequence of actions.

Around 10:30 p.m. on Monday, Juno passed over Jupiter’s north pole and through a region that Heidi Becker, the leader of Juno’s radiation monitoring team, described as “the scariest part of the scariest place.” In this belt of radiation, electrons bouncing back and forth at nearly the speed of light could have knocked out the computer and other electronics.

“They will go right through a spacecraft and strip the atoms apart inside your electronics and fry your brain if you don’t do anything about it,” Dr. Becker said.

But a titanium vault built for Juno proved up to the task of shielding its crucial systems.

At 11:18 p.m., Juno’s main engine began firing to slow the spacecraft enough to be captured by the planet’s gravity. Juno also passed through the plane of Jupiter’s diaphanous rings. Although the mission planners had chosen a place that they thought would be clear, they could not be certain, and even a piece of dust colliding with a spacecraft moving at 130,000 m.p.h. could have caused considerable damage.

Juno traveled within 2,900 miles of Jupiter’s cloud tops, passing through almost the exact spot that the navigators had aimed for after its 1.7-billion-mile voyage. “Isn’t that incredible?” Mr. Nybakken said.

Then Juno headed outward again, away from Jupiter. After the end of the engine burn, the spacecraft pivoted so that its solar panels were again facing the sun. Sunlight at Jupiter is one twenty-fifth as bright as at Earth, and Juno’s three 30-foot-long panels with 18,698 solar cells generate a mere 500 watts to power the spacecraft and its instruments.

“Now the fun begins, with science,” Dr. Bolton said.

For now, Juno is on a 53-day orbit. Its scientific instruments, which had been turned off for the arrival at Jupiter, will be turned back on in two days. On Aug. 27, it will swing back for its first good close-up look at Jupiter.

Juno will fire its engine again on Oct. 19 to move to a 14-day orbit, when the science measurements begin in earnest.

The spacecraft will have to make multiple flybys, Dr. Bolton said, before the scientists will be able to start answering questions like whether there is a rocky core at the center of Jupiter. “We’ll be hesitant to guessing the wrong answer until we see more information,” Dr. Bolton said.

With a different vantage point from Juno’s polar orbit, the spacecraft’s cameras are likely to add to the number of known moons of Jupiter, now 67. “I expect that we will see some, and the number will keep going up,” Dr. Bolton said.

The assault of radiation each time Juno zooms past Jupiter will take its toll on the electronics. As the mission progresses, the orientation of the orbits will pivot, and Juno will pass through the more violent portions of the radiation belts.

On the 37th orbit, scheduled for Feb. 20, 2018, Juno is to make a suicidal dive into Jupiter, ending the mission, the same way that the Galileo spacecraft was disposed of in 2003. That is to ensure that there would be no possibility of Juno’s crashing into Europa, regarded as one of the likelier places for life elsewhere in the solar system, and contaminating it with microbial hitchhikers from Earth.

Even in the best outcome, the mission might be extended a few months.

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