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5 Mysteries of Jupiter That Juno Might Solve

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Written by
Erik Gregersen
Erik Gregersen is a senior editor at Encyclopaedia Britannica, specializing in the physical sciences and technology. Before joining Britannica in 2007, he worked at the University of Chicago Press on the...
Erik Gregersen
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The Editors of Encyclopaedia Britannica
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.
The Editors of Encyclopaedia Britannica
Jupiter (planet, space, outer space, planetary, solar system).
© Byron Moore/Fotolia

The Juno spacecraft arrives at Jupiter on July 4, 2016, after a journey of nearly five years and 2.7 billion km (1.7 billion miles). It will be the first space probe to orbit Jupiter since Galileo plunged into that planet’s atmosphere in 2003.

  • How Did Jupiter Form?

    Asteroid - Artist's concept of Jovian Trojans - asteroids that lap the sun in the same orbit as Jupiter - showing both the leading and trailing packs of Trojans in orbit with Jupiter. Data from NASA's Wide-field Infrared Survey Explorer, or WISE
    Jovian TrojansArtist's conception of Jupiter's Trojan asteroids. Jupiter has two fields of Trojan asteroids, which orbit 60° ahead of and behind the planet.
    NASA/JPL-Caltech

    Jupiter is the most-massive planet in the solar system, and because it is so large, it retained all of the gas it was born with. Nothing could escape its gravitation by seeping into space, like the hydrogen in Earth’s atmosphere. By studying the composition of Jupiter, Juno will be able to identify the gas that the planet formed with 4.5 billion years ago and thus maybe learn how Jupiter came to be.

  • What Is the Great Red Spot Doing?

    Close up of red spot on Jupiter
    Great Red SpotThe Great Red Spot as seen by the Voyager 1 spacecraft during its 1979 flyby of Jupiter. The spot is an enormous storm system that has been continuously observed since 1878.
    NASA/JPL

    The Great Red Spot is a storm larger than Earth (about 16,500 km [10,250 miles] wide) that has been swirling since at least the 1830s and maybe even since the mid-17th century. Although it’s been observed for centuries, almost nothing is known about it. What is powering it? Why has it lasted for hundreds of years? Juno will get a very close view of the spot, from just 4,600 km (3,000 miles) away, which may clear up its mysteries.

  • Does Jupiter Have a Core?

    Cross section of Jupiter showing the outer atmosphere to the core. planets, solar system
    JupiterDiagram showing the internal structure of Jupiter from the outer cloud tops down to its core.
    Encyclopædia Britannica, Inc.

    Not much is known about the core of Jupiter, or even if it really has one at all. Scientists have speculated that Jupiter’s core is likely hydrogen that has been squeezed by the enormous weight of the atmosphere above it into a metallic form. As the probe’s velocity changes as it orbits the planet, the frequency of radio waves that Juno transmits to Earth will change. From these changes, Juno will measure Jupiter’s gravitational field and its internal structure precisely.

  • How Is Jupiter’s Magnetic Field Generated?

    Jupiter's magnetosphere is the largest object in the solar system. If visible to the eye, it would appear two to three times the size of the Sun or Moon to viewers on Earth.
    Jupiter's magnetosphereJupiter's magnetosphere as observed by the Cassini spacecraft in 2000. The magnetosphere is the largest object in the solar system.
    NASA/JPL/Johns Hopkins University Applied Physics Laboratory

    Jupiter has the largest magnetosphere of any planet. The magnetic field lines stretch out over a space 75 times bigger than the planet itself. Juno is teeming with instruments to study the charged particles trapped in Jupiter’s magnetic field. These measurements—when combined with the study of Jupiter’s deep internal structure, where the magnetic field is generated—will give a much better understanding of this powerful magnetosphere.

  • What Do Jupiter’s Poles Look Like?

    Jupiter's south pole taken by the Cassini spacecraft December 2000
    Jupiter's south poleJupiter's south pole as seen by the Cassini spacecraft in 2000.
    NASA/JPL/Space Science Institute

    Juno will be in a polar orbit around Jupiter in order to avoid encounters with the planet’s strong radiation belts, which could damage the spacecraft. Thus, Juno will be the first probe to get a close-up view of Jupiter’s poles. The polar regions of Jupiter are very interesting because of Jupiter’s powerful magnetosphere, which generates strong aurora. The auroral oval even has spots from which currents of plasma flow from Jupiter’s moons to the poles of the planet.