Jupiter News

Jupiter, in pastel colors because the observation was taken in near-infrared light, experiences a rare alignment of three of its large moons; Io, Ganymede, and Callisto.

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Celestial Lighthouse

    Magnetic Fields Give Us the Time of Day

    Deep inside Jupiter, the atmosphere is dense enough to act like a fluid metal. Due to Jupiter's fast rotation, this fluid generates a very strong, invisible, magnetic field, so large that if visible from Earth, it would appear larger than the Moon.


    Ultra violet image of Jupiter's aurora with moon footprints of Io, Ganymede and Europa.Aurora on Jupiter imaged in ultraviolet by NASA's Hubble Space Telescope
    Many planets have magnetic fields, including Earth, which is why a compass always points towards magnetic north. This field is also responsible for majestic aurorae on Jupiter, like the spectacular Northern and Southern Lights seen on the Earth. An aurora forms when energetic particles from the Sun interact with this invisible field and hit the upper layers of the atmosphere, causing it to glow. At Jupiter, small particles blasted off the surfaces of Io, Europa and other moons are also trapped by the magnetic field and the small footprint of each satellite can be seen.

    However, Jupiter's magnetic field is tilted relative to its rotation axis, such that the magnetic pole sweeps in and out of view like the light in a lighthouse. As particles hit the atmosphere near the magnetic pole, small energy bursts are released and can be detected by radio receivers, allowing us to measure the length of day on Jupiter. With no solid surface features to track, this is the only way to know how fast this giant planet spins.

    Image of moon compared to Jupiter Magnetosphere imposed over a night time earth horizon.


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