Juno Arrives at Jupiter

A NASA spacecraft has arrived at the solar system's largest planet after a picture-perfect orbital insertion.

NASA's Juno space probe ended a five-year, 1.7-billion mile trek to Jupiter on Monday, nailing a do-or-die braking burn to shave its speed and settle into orbit around the largest planet in the solar system.

Confirmation of Juno's safe arrival came at 11:53 p.m. EDT when flight controllers reported an expected shift in tones coming from the probe, a live NASA TV broadcast showed.

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"A big sigh of relief," said mission commentator Gay Yee Hill, at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Had the 35-minute burn of Juno's main engine failed, the spacecraft would have sailed past Jupiter, ending the mission before it began. Only one other spacecraft, NASA's Galileo probe, has orbited Jupiter.

Juno, named for the mythical Roman goddess who was the wife and sister of Zeus and who had the power to see through clouds, is designed to answer some key questions left over from Galileo's eight-year study of the Jovian system.

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Topping scientists' wish list is knowing how much water Jupiter contains, information that they can feed into computer simulations to calculate how and where the planet formed.

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"If Jupiter formed really far from the sun and drifted inward you'll get a different amount of water than if it formed where it is now," said Juno project scientist Steven Levin, at NASA's Jet Propulsion Laboratory.

Jupiter orbits about five times farther away from the sun than Earth.

"If it formed, as we think is likely, from icy planetesimals -- large chunks of ice that collided together -- and made a giant planet, then you'll get a different amount of water than if it formed some other way, such as directly condensing from the same material that made the sun," Levin said.

As the largest planet, Jupiter influenced the rest of the solar system's formation, including the location of Earth and its suitability for life.

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"By studying Jupiter you're going to get on piece of the puzzle, not necessarily how life formed but maybe how the ingredients that made up life eventually got spread around in the early solar system and got to us," said Juno lead scientist Scott Bolton, with the Southwest Research Institute in San Antonio, Texas.

To collect its data, Juno will spend 20 months flying as close as 3,000 miles from the tops of Jupiter's clouds, a position that leaves it vulnerable to the planet's massive radiation.

The spacecraft's electronics are protected inside a radiation-resistant titanium vault, but NASA expects to end the mission after 37 orbits, each of which will last 14 days.

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It will take Juno about six weeks to tweak its orbit and begin its science mission. On its final swing around Jupiter, Juno, like Galileo before it, will steer itself into the planet's crushing atmosphere to avoid possible contamination of the ocean-bearing moon Europa.

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Jupiter may be the solar system's Goliath, with more than twice as much material as all its sibling planets combined, but its got a small tilt. Its relatively puny 3.13 degree axial tilt (compared to Earth's 23.5-degree pitch, for example) means Jupiter doesn't experience much in the way of seasons.

Image: Powerful aurora, year-round. Credit: NASA/ESA/STSci

No one gets credit for discovering Jupiter, the fourth brightest object in the night sky after the sun, the moon and Venus. According to May, 1974 paper published in the Philosophical Transactions of the Royal Society of London (which calls itself the world's first science journal), observations of Jupiter date back to Babylonian sky-watchers 2,700 or so years ago. Galileo Galilei is credited with discovering four large moons circling Jupiter in 1610, the first objects found to orbit another planet. Jupiter's moon count currently numbers 67.

Image credit: NASA

The gravitational warping of space caused by Jupiter's extreme mass affects the orbits of other planets and other celestial bodies in the solar system. Jupiter has been referred to as the solar system's vacuum cleaner because its gravitational well catches comets and other bodies coming in from the outer solar system. In 1994, astronomers for the first time witnessed a collision between objects in the solar system, observing more than 20 fragments from the doomed comet Shoemaker-Levy 9 smashing into Jupiter.

Photo credit: H. Hammel/MIT/NASA

Jupiter has been visited by eight spacecraft, though only Galileo -- and soon Juno -- has gone into obit. Galileo carried a secondary spacecraft that plunged into Jupiter's atmosphere on Dec. 7, 1995, relaying data for 58 minutes before succumbing to the high pressure and temperature.

Artist rendering of Juno flying over Jupiter's north pole. Credit: NASA/JPL-Caltech

One of Jupiter's most prominent features is a huge storm located about 22 degrees south of the planet's equator. The so-called "Great Red Spot" was first observed through telescopes on Earth in the 17th century. NASA's Voyager spacecraft relayed the first close-up images of the storm as it approached Jupiter in 1979.

Photo credit: NASA

The magnetic field of Jupiter is the largest structure in the solar system after the heliosphere itself, extending more than 4 million miles in the direction of the sun and almost to the orbit of Saturn. Jupiter's magnetosphere is nearly 20,000 times stronger than Earth's. Like Earth's, Jupiter's magnetosphere traps and speeds up particles, which produce radiation belts similar but thousands of times stronger than the Van Allen belts. To protect Juno's instruments from the radiation, its sensitive electronic instruments are housed in a 400-pound titanium box.

Photo credit: NASA

Jupiter has the shortest day of any planet in the solar system, completing a rotation in a little less than 10 hours. Located about five times farther away from the sun than Earth, Jupiter takes almost 12 years to cycle around the sun.

Photo credit: NASA, ESA, and E. Karkoschka (University of Arizona)

Beneath Jupiter's massive atmosphere, which is mostly made of hydrogen, are layers of compressed hydrogen gas, liquid metallic hydrogen and possibly a core of ice, rock and metals. Determining if Jupiter has a dense core is one of the goals of the Juno mission.

Image: Three-dimensional visualization of Jupiter's cloud decks. Credit: Galileo Project/JPL/NASA

Jupiter currently orbits about five times farther away from the sun than Earth, but it may not have always been there. Some scientists suspect Jupiter may have migrated into the inner solar system early in its history, destroying a first-generation family of planets before retreating into its current orbit. One of Juno's goals is to measure how much water Jupiter contains, information scientists can use to figure out where Jupiter formed.

Photo credit: NASA/JPL/Space Science Institute

Most of the material left over after the sun's formation some 4.6 billion years ago ended up as part of Jupiter. Scientists aren't sure why, but they expect data relayed over the next 20 months from the Juno spacecraft will help piece together the story of how our solar system -- and others elsewhere in the galaxy -- evolved.

Image: Artist impression of a young planetary system. Credit: STSci