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Ten Things You Need to Know About the Juno Mission

Get up to speed on the ways this daredevil probe will unlock Jupiter’s secrets, and find out some of Juno’s unique features.

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NASA’s solar-powered Juno spacecraft arrived at Jupiter on July 4, 2016.


After a daring, perfectly executed plunge through the most intense radiation a spacecraft has ever survived, NASA’s Juno probe pulled into orbit around Jupiter last night.

To mark the occasion, NASA unveiled a video providing a Juno’s-eye view of the fifth world from the sun, shot as the spacecraft approached the giant planet. The video is a time lapse of images taken between June 12 and 29.

In it, you can see Jupiter surrounded by four large moons, gracefully orbiting in lockstep and slipping in and out of the planet’s shadow. These are the Galilean moons, observed in 1610 by the famed Italian astronomer in a discovery that would splinter existing ideas about Earth’s place in the universe. By orbiting Jupiter, the moons proved that not everything revolved around the Earth, which was long believed to be the center of the cosmos.

Dance of the Galilean Moons

This time lapse shows what Juno saw as it approached Jupiter. (Video by NASA/JPL)


The nearest moon to Jupiter is volcanic Io, the most fiery and tempestuous world in the solar system. Then comes Europa, the ice-encrusted moon many consider to be the most likely host for extraterrestrial life. Next out is Ganymede, the largest moon of them all (it’s bigger than the planet Mercury), and last is cratered Callisto, which mission scientists note was surprisingly dim in this video.

For the next two years, the spinning, solar-powered spacecraft will trace loops around the solar system’s largest planet as it attempts to solve some appropriately super-sized mysteries. While we wait for the Juno team to turn on the spacecraft’s instruments and release some new images, here are some fun facts about the mission, the spacecraft, and the world it now calls home:

Juno is named after a Roman goddess who could see through clouds.

The craft’s name is exceptionally appropriate, given its task of sorting out what lies beneath Jupiter’s beautiful, swirling cloud tops. Perhaps better known by her Greek name Hera, Juno was Jupiter’s (Zeus’s) wife. In Roman mythology, Jupiter cast a veil of clouds around himself to conceal his indiscretions—but Juno was able to peer through Jupiter’s shroud and discern his real character.

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These three LEGO figurines are flying aboard the Juno spacecraft.


Can you guess who they are? One is the Italian astronomer Galileo, known for discovering Jupiter’s four large moons. The other two are Juno, the goddess after whom the mission is named, and Jupiter himself. Lego Juno is carrying a magnifying glass, which signifies her search for the truth. Jupiter is holding a lightning bolt, and Galileo has a telescope and a mini-Jupiter in his hands.

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The plaque dedicated to astronomer Galileo Galilei was provided by the Italian space agency.


Juno is also carrying a plaque inscribed with some of Galileo’s writings from 1610.

Donated by the Italian Space Agency, the plaque replicates a page from Galileo’s notes recording the discovery of Jupiter’s four large moons. From an earlier blog post, here’s how this crucial observation unfolded:

Galileo described the first cluster of icy satellites, the four largest around Jupiter, in the early 1600s. Night after wintry night, he watched as three strange “stars” swirled around the giant planet. The stars weren’t behaving as he’d expected, and traced odd patterns in the sky. Gradually, Galileo realized that his stars swore allegiance to great old Jupiter rather than the glittering black backdrop. After several months, Galileo concluded that he was not, in fact, seeing stars. He was watching planetary bodies moving around giant Jupiter—and there weren’t just three of them, but four.

“I should disclose and publish to the world the occasion of discovering and observing four Planets, never seen from the beginning of the world up to our own times,” Galileo wrote in his Sidereus Nuncius. “I summon all astronomers to apply themselves to examine and determine their periodic times, which it has not been permitted me to achieve up to this day.”

Just like that, the Galilean moons were described. They wouldn’t be known as Ganymede, Callisto, Io, and Europa for another 250 years. Those were not the names proposed by Galileo, who instead called them the “Medicean planets,” after the powerful Medici family, whose influence had spread throughout Europe. Rather, it was German astronomer Johannes Kepler who suggested naming the quartet after Jupiter’s collection of lovers.

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Seen in February 2011, technicians at a facility in Colorado test one of Juno's huge solar arrays.


Juno is humanity’s most distant solar-powered explorer.

Normally, spacecraft sailing into the outer solar system carry a radioactive power source, but Juno relies on three enormous solar panels to harvest the sun’s energy. Each of these panels is 29 feet (8.9 meters) long and covers 256 square feet (about 24 square meters), or more surface area than some studios for rent in San Francisco. Juno can use solar energy because its nine science instruments are extremely energy efficient, and its orbit around Jupiter never takes it through the planet’s shadow, meaning its energy-harvesting cells are always facing the sun.

Juno is scheduled to end its life by plunging into Jupiter in 2018.

It won’t be the first spacecraft to die inside Jupiter, though: The Galileo space probe, which orbited the giant planet between 1995 and 2003, ended its mission in similarly dramatic style. Why destroy spacecraft in such a crushing fashion? NASA wants to eliminate the chances of a defunct spacecraft accidentally crashing on one of the Jovian moons (namely, Europa) and contaminating it with hitchhiking, Earthly microbes.

You, too, can use Juno to study Jupiter.

Over the coming weeks, anyone with an internet connection can vote on where the JunoCam instrument should point during Juno’s science orbits, and therefore have a say in which images of the planet system come back to Earth.

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This Hubble image shows brilliant auroras on Jupiter's north pole.


The spacecraft will stare at the most immense, intense auroras in the solar system.

Jupiter has the strongest magnetic field of any planet orbiting the sun, and its polar auroras are correspondingly magnificent, sometimes spanning the width of many Earths. As the spacecraft maps the Jovian magnetic field, it will begin to uncover exactly how to generate these spectacular light shows.

Juno will seek to answer: Does Jupiter have a core?

It sounds like a simple question, but it’s not. Scientists don’t know if there’s a solid, rocky surface hiding beneath all those beautiful spots and bands. But they suspect not. Instead, prevailing theories suggest that as pressures build deep within the planet, the hydrogen and helium gases dominating Jupiter’s atmosphere are squeezed into extremely exotic forms—perhaps leaving the planet with a core made of swirling metallic hydrogen.

The spacecraft will be hunting for water.

It might not be the most obvious question, but it’s one that will help scientists understand how, when, and where Jupiter formed—as well as what conditions in the early solar system were like. As the largest planet, Jupiter likely formed first, sweeping up and collecting whatever ingredients were hanging around the young sun. By measuring how much water the planet contains, scientists will be able to learn more about what those ingredients were like, which could resolve a debate about whether Jupiter formed close to its current location or migrated outward as it aged.

Not every part of Juno is expected to survive until the end of the mission.

Jupiter’s intense magnetic field is slinging charged particles around in epic planetary fashion, often accelerating them to near light-speed. So, belts of radiation surrounding the planet—which were first hypothesized to exist back in 1959—are more than strong enough to destroy the sensitive electronics riding aboard Juno. To slow down this somewhat inevitable process, engineers encased the spacecraft’s computer in a 400-pound (181 kilogram) titanium vault and shrouded each of its instruments with smaller shields.

But it won’t be enough to protect Juno indefinitely. Though the spacecraft’s orbit is designed to avoid the most intense bands of radiation, the mission team fully expects the electronics to degrade as the mission goes on. In fact, JunoCam is only designed to survive seven or eight orbits of the planned 22 science orbits.

Follow Nadia Drake on Twitter.

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