Exploring Jupiter’s Magnetic Field

Magnetic fields are all around us, unseen forces that can shape their environments in profound ways. Earth’s magnetic field shields us from the solar wind, but the dynamo that generates it is hidden from view by the magnetized rock beneath our feet. Aside from the Sun, the solar system’s largest magnetosphere belongs to Jupiter – a gargantuan magnetic windsock with a tail stretching out to the orbit of Saturn. Now, NASA is sending the Juno spacecraft to peer beneath Jupiter’s clouds, giving scientists their first glimpse of the dynamo driving this giant magnetic field.

Magnetospheres are the result of a collision between a planet’s intrinsic magnetic field and the supersonic solar wind. Jupiter’s magnetosphere — the volume carved out in the solar wind where the planet’s magnetic field dominates –extends up to nearly 2 million miles (3 million kilometers). If it were visible in the night sky, Jupiter’s magnetosphere would appear to be about the same size as Earth’s full moon. By studying Jupiter’s magnetosphere, scientists will gain a better understanding about how Jupiter’s magnetic field is generated. They also hope to determine whether the planet has a solid core, which will tell us how Jupiter formed during the earliest days of our solar system.

In order to look inside the planet, the science team equipped Juno with a pair of magnetometers. The magnetometers, which were designed and built by an in-house team of scientists and engineers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will allow scientists to map Jupiter’s magnetic field with high accuracy and observe variations in the field over time.

The magnetometer sensors rest on a boom attached to one of the solar arrays, placing them about 40 feet (12 meters) from the body of the spacecraft. This helps ensure that the rest of the spacecraft does not interfere with the magnetometer.

However, the sensor orientation changes in time with the mechanical distortion of the solar array and boom resulting from the extremely cold temperatures of deep space. This distortion would limit the accuracy of the magnetometer measurements if not measured.

To ensure that the magnetometers retain their high accuracy, the team paired the instruments with a set of four cameras. These cameras measure the distortion of the magnetometer sensors in reference to the stars to determine their orientation.

One of the mysteries the team hopes to answer is how Jupiter’s magnetic field is generated. Scientists expect to find similarities between Jupiter’s magnetic field and that of Earth.

Magnetic fields are produced by what are known as dynamos — convective motion of electrically conducting fluid inside planets. As a planet rotates, the electrically susceptible liquid swirls around and drives electric currents, inducing a magnetic field. Earth’s magnetic field is generated by liquid iron in the planet’s core.

NASA’s Goddard Space Flight Center.
Jet Propulsion Laboratory.
Southwest Research Institute.

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