When Juno Meets Jupiter: NASA's Fastest Spacecraft to Enter Planet's Orbit

Juno and Jupiter
NASA's Juno spacecraft has entered orbit around Jupiter. This artist's rendering shows Juno making one of its close passes over Jupiter. NASA/JPL-Caltech

Almost exactly a year after NASA's New Horizons spacecraft made history with the first-ever flyby of Pluto, the agency's Juno spacecraft is scheduled to enter orbit around Jupiter.

"We could not be more excited being back on Jupiter's doorstep," Diane Brown, Juno program executive at NASA, said at a media briefing Thursday. NASA "has been to Jupiter before but never this close," she added, giving a nod to earlier exploration of the planet—the flybys (Pioneers 10 and 11 and Voyagers 1 and 2) and most recently the Galileo orbiter, which ended its mission in 2003.

"We look forward to making our own fireworks this year."

Juno launched from Cape Canaveral in Florida on August 5, 2011, and has been hurtling through the interplanetary solar winds of space toward the largest planet in our solar system for nearly five years. By the time NASA attempts Monday's "Jupiter Orbit Insertion (JOI)," as the agency refers to it, the spacecraft will have traveled more than 1.7 billion miles.

The Juno mission's fundamental goal is to help scientists understand how Jupiter formed and evolved, which in turn reveals more about our entire solar system and other solar systems. "As our primary example of a giant planet, Jupiter can also provide critical knowledge for understanding the planetary systems being discovered around other stars," the mission overview reads. Juno will collect data about Jupiter's structure and composition, temperature, cloud movements, magnetic and gravity fields, atmosphere and auroras. The spacecraft will determine how much water Jupiter has, for example, a measurement that can reveal a great deal about how and where Jupiter formed and about the origins of the solar system.

At the time of launch, Juno weighed 7,992 pounds, including the spacecraft as well as fuel and oxidizer. With three 29.5-foot-long solar arrays extending from its center, Juno is roughly the size of a basketball court. A titanium vault in the center stores sensitive electronics to protect them from the intense radiation near Jupiter.

Juno's main engine cover has been opened, and the spacecraft has already entered Jupiter's magnetosphere—"We've just crossed the boundary into Jupiter's home turf," Juno Principal Investigator Scott Bolton was quoted as saying in a NASA press release.

Mission control sent a command sequence Thursday to the spacecraft, instructing Juno to go into autopilot in preparation for the orbit insertion. "Getting something in orbit around a massive planet is not easy, OK, it's not trivial," Jim Green, director of planetary science, tells Newsweek. "This is really the critical maneuver," he adds. Juno would get thrown out into space unless it can be slowed down, Green explains. The plan is to flip the spacecraft and then execute a 35-minute burn of the engine against the direction Juno is traveling. The slowing of the spacecraft should allow it to be captured into a polar orbit around Jupiter, moving in an elliptical path high over the North and South poles of the planet and getting as close as 2,600 miles to Jupiter's cloud tops.

If it's successful, Juno would also be the first-ever space mission to enter a polar orbit around Jupiter, allowing scientists to get a view of the entire planet.

The 35-minute Jupiter Orbit Insertion burn is scheduled to begin Monday night at 8:18 p.m. PT or 11:18 p.m. ET. Though most instruments will be turned off while Juno attempts this "critical maneuver," the team will be in radio communication with the spacecraft, which will let them know if the engine shuts off early or if something goes wrong. By midnight on the east coast, they should know for sure whether Juno has successfully entered orbit.

The public can follow along with live coverage of the event broadcast on NASA TV starting at 10:30 p.m. ET. While the spacecraft is in orbit in subsequent months, "everyone will have a chance to see exactly what Juno is seeing" through data and high resolution images from the Juno Cam, Green says.

"We cannot be ignorant about our place in the solar system. We cannot be ignorant about how our planet changes," Green says.

Juno could help scientists grapple with "what is in store for us as a species," he adds. "We really cannot just assume everything will be alright—we have to understand."