THE SCIENCE OF JUPITER
Like the Sun, Jupiter is made almost entirely of hydrogen and helium. But it’s so big that its enormous mass exerts tremendous inward pressure. The pressure squeezes the interior hydrogen so strongly that the gas turns into a liquid – a strange type of hydrogen that can even conduct electricity. This churning, conducting fluid is likely the engine behind Jupiter’s magnetic field, which is the largest and strongest in the solar system, except for the Sun’s.
Jupiter formed when gas and dust – left over from the formation of the sun – collected into a large sphere. The ball of gas was so massive that its own gravity caused it to contract – and four and a half billion years later, Jupiter is still shrinking.
As Jupiter contracts, all the matter inside squishes against itself and churns, causing friction and heat. As the warmer material deep inside rises, some of Jupiter’s contents are partially mixed up in the process. Eventually, the heat is released into space. In fact, Jupiter radiates more heat than it absorbs from the Sun.
The stirring motion of Jupiter’s hot interior also generates its magnetic field. This magnetic field creates a huge bubble of electrically charged gas called the magnetosphere. The magnetosphere is so large that it would look as big as the moon if it were visible in the night sky.
As Jupiter spins – at a brisk rate of once every 10 hours – it drags its magnetic field around with it, which creates strong electric currents. Earth has a similar feature – a ring of charged particles called the Van Allen Belt – but at a much smaller scale. Because the charged particles in Jupiter’s belt fly around extremely fast, this region is filled with radiation that can destroy a spacecraft.
Armed with an arsenal of scientific instruments, Juno will explore four main aspects of Jupiter: its origin, interior, atmosphere, and magnetosphere.
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Jupiter’s magnetic field exerts its influence over a vast bubble of charged particles called the magnetosphere.
Jupiter's MagnetosphereExtending beyond Jupiter’s moons, the Jovian magnetic field is the strongest in the solar system, except for the Sun’s. The field dominates an expansive region called the magnetosphere - the largest structure in the solar system. The magnetic field accelerates electrically charged particles that stream through the magnetosphere. Most of these particles, which are ionized and swept up by the field, come from the volcanic gases spewing from Jupiter’s moon Io.
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Jupiter’s origin is deeply connected to our own, so exploring the giant planet helps us understand where we came from.
OriginThe solar system formed 4.5 billion years ago, when a giant cloud of gas and dust collapsed. Most of this material became the sun and most of what was left over became Jupiter. But many details of this story remain a mystery – how or why this cloud collapsed in the first place, for instance. Jupiter, however, can reveal some of these details.
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JUPITER AND OUR SOLAR SYSTEM
Why is Jupiter so important to the solar system?
Jupiter and our Solar SystemWith the exception of the Sun, Jupiter is the most dominant object in the solar system. Because of its size and the fact that it was the first of the gas-giant planets to form, it has profoundly influenced the formation and evolution of all the other planets. For example, Jupiter is the reason why there’s an asteroid belt – and not another planet - between it and Mars. Jupiter has also catapulted countless comets out to the edge of the solar system. Like a gatekeeper, Jupiter has safeguarded Earth from many comet impacts.
The planets are the leftovers from the star-forming process, and Jupiter accounts for the bulk of that material - more than twice that of all the other planets combined. Its atmosphere - predominantly hydrogen and helium - is similar to the composition of the sun and other stars as well as the clouds of gas and dust in our galaxy.
When the sun was born – when it accumulated enough mass for nuclear fusion to ignite – it generated a wind that blew away most of the gas and dust that still remained. The fact that Jupiter’s composition is similar to that of the original cloud suggests that it formed early on, before the wind could clear away that material.
To give you an idea of how dominant Jupiter is, an alien observing our solar system through a telescope would see an average yellow star and Jupiter with three other large planets. Earth and the inner planets would appear merely as debris.
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Does Jupiter have a solid core? How does it create the largest magnetic field in the solar system, apart from the Sun?
The InteriorThe structure of Jupiter’s interior is a mystery. Juno will investigate the giant planet’s interior structure and search for a core by mapping its magnetic and gravity fields very precisely.
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Formed from small moons, thin rings of dust particles surround Jupiter.
Jupiter's RingsSaturn is famous for its brilliant, icy rings. But all of the gas giants in the solar system have rings – including Jupiter. Unlike Saturn’s rings, Jupiter’s are thin and wispy. And while Galileo first saw Saturn’s rings in 1610, Jupiter’s rings were not discovered until the 1970s, when the Voyager spacecraft visited the planet.
Jupiter’s rings likely formed when chunks of rock or ice crashed into the small moons that now reside within the rings. The collisions blasted dust into space that then encircled the planet.
The ring system is composed of three main parts. On the outside, there’s a pair of faint, gossamer rings. The outermost ring is enclosed inside the orbit of Thebe, one of Jupiter’s moons. The orbit of another moon, Amalthea, forms the outer boundary of the second gossamer ring.
The moons Adrastea and Metis skirt the edges of the flat main ring, which is 6,500 kilometers (4,000 miles) wide.
The third component is made of the same particles as the main ring, but the electromagnetic forces from Jupiter’s magnetosphere shape it into a thick, doughnut shape. Called the halo, it’s about 20,000 to 40,000 kilometers (12,400 to 25,000 miles) thick, although most of the material lies within a few hundred kilometers of the ring plane.
How do the Juno scientists test and prepare instruments for Jupiter’s extreme radiation environment?
SHOEMAKER LEVY 9 IMPACT
In 1994, a comet smashed into Jupiter, creating a cosmic spectacle that caught the world’s attention.
Collisions with JupiterJupiter is the guardian of the inner solar system. Its powerful gravitational field draws comets and other space rocks away from Earth and its neighbors. We now understand how these small objects speed around the solar system far better than ever before, and it turns out that planetary collisions may be more frequent than previously thought. In 1994, comet Shoemaker-Levy 9 gave a spectacular show when it hurtled toward Jupiter, smashing into its thick clouds.
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Are the swirls and bands on Jupiter mere surface features, or do they extend deep into the planet?
The Atmosphere of JupiterJupiter’s stunning appearance is due to its atmosphere of swirling clouds and colorful bands, which alternately flow east and west. The atmosphere is mostly hydrogen and helium, but the visible clouds are ammonia. Underneath, there are water clouds. Even after over 200 years, the winds have largely remained unchanged, although the intensity of the colors and width of the bands have varied. The famous Great Red Spot, as big as two Earths, is at least 300 years old. The reds, oranges and other colors arise from chemical reactions, which are probably driven by processes like lightning.
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MOONS OF JUPITER
Jupiter has more than 60 moons – some larger than ours – and at least one that could harbor life.
Jupiter's MoonsWhen Galileo discovered Jupiter’s four largest moons in 1610, he noticed the resemblance to the solar system - a finding that would help knock down the idea of an Earth-centered universe. Indeed, these four moons are like full-fledged planets. Ganymede has its own magnetic field, Io is pockmarked with volcanoes, Europa may have an ocean under a thick layer of ice and, as the third largest moon in the solar system, Callisto is about the size of Mercury.
In total, there are more than 60 moons. The four Galilean moons, as they’re called, likely formed when Jupiter did. The others were probably captured by Jupiter’s gravity. The moons with closer orbits create thin, faint structures around Jupiter called gossamer rings.
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WHAT DOES JUPITER SOUND LIKE?
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What Does Jupiter Sound Like?