Juno Helps Find Changes in Jupiter's Magnetic Field

NASA's Juno spacecraft has gathered data that helped determine secular variation on Jupiter.
Jessica Miley
NASA/JPL-Caltech/Harvard/Moore et al.

NASA’s Juno Spacecraft has once again proved it's worth announcing another exciting discovery. The hardworking Juno team has made the first definitive detection of an internal magnetic field that changes over time on another planet.


This phenomenon is known as secular variation and will help scientists understand more about the makeup of Jupiter's interior. Juno has determined that secular variation is most likely driven by the planet's deep atmospheric winds.

Super detailed data gets results

Details of the discovery have been published in the journal Nature Astronomy. "Secular variation has been on the wish list of planetary scientists for decades," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio.

"This discovery could only take place due to Juno's extremely accurate science instruments and the unique nature of Juno's orbit, which carries it low over the planet as it travels from pole to pole."

Understanding a magnetic field requires highly detailed observations. To gather enough data NASA used information from past Jupiter missions (Pioneer 10 and 11, Voyager 1 and Ulysses) with a model of Jupiter's magnetic field that was created from data collected by Juno during its multiple passes of Jupiter.

Juno proves worthy once again

The data was collected using a specialized piece of equipment known as a magnetometer - which is capable of generating a detailed three-dimensional map of the magnetic field. What especially interested NASA is the small but detectable differences in the magnetic field that they were able to observe by looking at the data over time.

"Finding something as minute as these changes in something so immense as Jupiter's magnetic field was a challenge," said Kimee Moore, a Juno scientist from Harvard University in Cambridge, Massachusetts.

"Having a baseline of close-up observations over four decades long provided us with just enough data to confirm that Jupiter's magnetic field does indeed change over time."

Jupiter's strong winds are key to field changes

Now that they have proved secular variation did occur, the team was curious to determine exactly why. It seems that Jupiters famous atmospheric or zonal winds provide the best explanation for this change in the magnetic field.

The powerful winds extend from the planet's surface to over 3,000 kilometers deep and are though to shear the magnetic fields, stretching them and carrying them around the planet. Jupiter has one spot where this is most noticeable, in a place known as the planet's Great Blue Spot.

This ‘spot’ has an intense magnetic field located near the planets equator. This intense field and strong localized winds make the Great Blue Spot an area where the largest secular variations were documented.

It is incredible that one narrow magnetic hot spot, the Great Blue Spot, could be responsible for almost all of Jupiter's secular variation, but the numbers bear it out," said Moore.

With this new understanding of magnetic fields, during future science passes we will begin to create a planetwide map of Jupiter's secular variation. It may also have applications for scientists studying Earth's magnetic field, which still contains many mysteries to be solved."

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