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.
About 5.3 million kilometers (3.3 million miles) wide on average, the magnetosphere is 150 times wider than Jupiter itself and almost 15 times wider than the Sun.
Jupiter’s magnetic field funnels some of the charged particles in the magnetosphere toward the poles, where they interact with the atmosphere to produce brilliant auroras – northern and southern lights. Juno’s orbits around Jupiter’s poles are designed to allow the spacecraft to measure the gravitational and magnetic fields, and the amount of water in the atmosphere. But they will also enable Juno to venture into unexplored regions of the magnetosphere and observe the auroras in unprecedented detail, learning more about the processes that control them.
In particular, Juno’s instruments will count the number of charged particles that trigger auroras. And the plasma- and radio-wave instruments will take ultraviolet and infrared images to understand how the magnetic field accelerates these particles.
The magnetosphere also enables us to measure how fast Jupiter spins.
Observing Jupiter’s clouds doesn’t help because they rotate at varying speeds and are not directly connected to the planet’s interior. But the magnetosphere rotates along with Jupiter because it’s driven by the magnetic field, which is generated deep inside the planet.
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HOW BIG IS THE MAGNETOSPHERE?
Jupiter’s magnetosphere is 150 times wider than the planet itself, and its tail stretches all the way to Saturn’s orbit.
HOW BIG IS THE MAGNETOSPHERE?As the largest structure in the solar system, the magnetosphere is about 21 million kilometers (12 million miles) wide. That’s 150 times wider than the planet itself and almost 15 times wider than the sun. If the magnetosphere were visible from Earth, it would appear as big as the moon. The solar wind, composed of charged particles ejected from the Sun, streams past Jupiter, elongating the shape of the magnetosphere into a teardrop. Its tail stretches all the way to Saturn’s orbit, twice as far from the Sun as Jupiter.
WHAT IS THE MAGNETOSPHERE?
Co-Investigators Fran Bagenal and Jeremy Bloxham describe the source of Jupiter’s magnetic personality.
WHAT IS THE MAGNETOSPHERE?
TAKING ADVANTAGE OF JUNO’S SPECIAL ORBIT
The spacecraft’s special orbit provides access to an unexplored region of Jupiter.
Juno's OrbitJuno’s orbit takes it over Jupiter’s poles, allowing the spacecraft to avoid most of the harmful radiation that encircles the planet. Juno’s trajectory also provides a spectacular tour over an unexplored part of Jupiter. The spacecraft will journey through a region called the polar magnetosphere, where charged particles pour into the planet’s atmosphere, creating a dazzling display of energy and light called auroras.
The unique orbit allows Juno to watch the auroras in high resolution with infrared, ultraviolet and visible-light cameras. The craft will also sample the streams of charged particles that generate these polar light shows. Additionally, it will measure the magnetic and electric fields that guide and power these particles. Juno will also listen to radio signals produced by the processes that spark the auroras.
Jupiter is surrounded by a belt of radiation stronger than any in the solar system, except for the Sun.
RADIATION BELTSSurrounding Jupiter is a belt of radiation and charged particles - protons, electrons, and ions – like an electric doughnut. These particles fly around and can damage electronics, posing a hazard for any spacecraft visiting Jupiter. Earth has similar - albeit weaker - rings of radiation called the Van Allen Belts.
To keep Juno safe from radiation, its most sensitive electronics are protected in a shielded container.
WHAT IS PLASMA?
Plasma is an electrically charged gas.
WHAT IS PLASMA?A mixture of freely flowing electrons and ions, a plasma is a distinct state of matter, in addition to gases, liquids and solids. Plasma is also the most common form of matter, making up more than 99 percent of the visible universe. It’s in stars and in the tenuous wisps of gas that fills the voids between them.
A plasma forms when gas becomes ionized – when atoms gets stripped of their electrons, producing an electrically charged soup of electrons and ions. This can happen inside Jupiter, where the tremendous pressure and scalding temperatures squeeze electrons off atoms. In space, stray electrons zipping around can knock an electron off a neutral atom. Ultraviolet light, in the form of high-energy photons, can also ionize gases to make plasma.
Since plasma is electrically charged, it’s influenced by electric and magnetic fields. Jupiter’s magnetic field, for example, confines plasma inside its magnetosphere, channeling and pumping it through space, which generates various phenomena like Jupiter’s auroras, radiation belts and radio signals.
WHAT ARE AURORAS?
Brilliant displays of light illuminate a ring around Jupiter’s poles when charged particles slam into its atmosphere.
WHAT ARE AURORAS?On Earth, auroras – or the northern and southern lights – appear as brilliant ribbons of shimmering light across the sky. These displays are triggered when Earth’s magnetic field funnels electrically charged particles into the planet’s atmosphere near the poles. To see the light shows, you have to be close enough to the poles.
Since Jupiter has the strongest magnetic field of any planet, its auroras are the brightest in the solar system – sometimes 10 times brighter and 100 times more energetic than Earth’s. In fact, the charged particles that bombard Jupiter’s poles dump more energy onto the atmosphere than sunlight. The auroras are visible as a glowing ring around Jupiter’s poles, and they’re especially brilliant in ultraviolet and infrared light.
As Jupiter spins, so does its magnetic field, sweeping through the electrically charged gas that fills the magnetosphere. It turns out that the magnetic field’s interaction with the charged gas – called plasma – slows down Jupiter’s rotation. Because of this interaction, Jupiter’s rotation energy is transferred into the plasma and eventually takes the form of the bright auroras. A similar process happens with other astronomical objects with magnetic fields, such as the Sun early in its history and other young stars.
The rotation of the plasma in Jupiter’s magnetosphere is the main engine that drives the auroras. Earth’s auroras, on the other hand, are fueled by the energy of the solar wind – gusts of charged particles flowing from the sun at millions of miles per hour.
Jupiter’s moons are another energy source that powers the auroras. Jupiter’s magnetic field interacts with Io, Europa and Ganymede in such a way that it channels charged particles between the planet and its moons, creating imprints of bright spots along the glowing auroral rings. The solar wind may also play a role in changing the patterns of light near Jupiter’s poles.
Needless to say, the exact processes that produce Jupiter’s auroras are complex and not well understood. But Juno aims to change that.