Magnetometer (Juno)

Magnetometer (MAG) is the name of an instrument suite on the Juno orbiter for planet Jupiter. The MAG instrument includes both the Fluxgate Magnetometer (FGM) and Advanced Stellar Compass (ASC) instruments. There two sets of MAG instrument suites, and they are both positioned on the far end of on three solar panel array booms. Each MAG instrument suite observes the same swath of Jupiter, and by having two sets of instruments, determining what signal is from the planet and what is from spacecraft is supported. Avoiding signals from the spacecraft is another reason MAG is placed at the end of the solar panel boom, about 10 m (33 feet) and 12 m (39 feet) away from the central body of the Juno spacecraft. The MAG instrument is designed to detect the magnetic field of Jupiter, which is one of the largest structures in the Solar System. If one could see Jupiter's magnetic field from Earth, it would appear five times larger than the full moon in the sky despite being nearly 1700 times farther away. Jupiter's internal magnetic field prevents the solar wind, a stream of ionized particles emitted by the Sun, from interacting directly with its atmosphere, and instead diverts it away from the planet, effectively creating a cavity in the solar wind flow, called a magnetosphere, composed of a plasma different from that of the solar wind.

Mission goals:

Jupiter has the strongest and biggest magnetic fields know to exist in the solar system. Studying these fields is one of the goals of the Juno mission, and in particular the task rests on the Magnetometer instruments. MAG measures the field about 60 times per second, and records the direction and strength of the field. MAG collected data on Earth during its October 9, 2013 flyby en route to Jupiter (this was a gravity assist maneuver, but also was to collect data).

There is another advantage to studying Jupiter's field, which is that on Earth crustal magnetism interferes with measurements of the field generated deep in the core, partially shielding it from measurements. On Earth the field is generated by spinning liquid iron, whereas on Jupiter is generated by hydrogen. Jupiter is mostly hydrogen (about 90%), and as it compresses from gravity it turns conductive in a special form. However, it is not known if farther in where it should compress to metallic hydrogen, if that is conducting electricity also. That is one of questions Juno will hopefully answer. In addition to studying Jupiter, the MAG also returned data on the Earth's magnetosphere.

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