The Earth's magnetic field changes all the time, and it is the only planetary field in which we have consistent measurements. But knowing the latest information is also very important, as changes can reveal minute details of a planet's internal dynamo, which is the system that produces the planet's magnetic field.
In a paper published on May 20 in the journal Nature Astronomy, researchers looked at magnetic field data from four previous missions to Jupiter. They compared the retrieved data to a map of the planet's magnetic field created by the spacecraft Juno, which conducted the most recent and most thorough probe of the planet. In 2016, Juno orbited very close to Jupiter, passing from pole to pole and gathering detailed magnetic and gravitational field data. That allowed the researchers to develop a model of Jupiter's magnetic field and detailed theories as to how it is made.
"Finding something as minute as these changes in something so immense as Jupiter's magnetic field was a challenge," Kimee Moore, a Juno scientist at Harvard and lead author on the paper, said in a statement. "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."
The researchers were only interested in the changes of Jupiter's internal magnetic field, but the planet also has magnetism coming from its upper atmosphere. Charged particles from volcanic eruptions on Jupiter's most volatile moon, Io, end up in the Jovian magnetosphere and ionosphere and can also change the magnetic field.
But the researchers developed methods to remove those effects from their data set, leaving them with data that is based almost entirely on the internal dynamo of the planet.
"These winds extend from the planet's surface to over 1,860 miles (3,000 kilometers) deep, where the planet's interior begins changing from gas to highly conductive liquid metal. They are believed to shear the magnetic fields, stretching them and carrying them around the planet," the statement said.
Most of those wind-driven changes are concentrated in Jupiter's Great Blue Spot which is intense magnetic energy near Jupiter's equator. The southern and northern parts of the blue spot are shifting east on Jupiter and the central third is shifting west, causing changes to Jupiter's magnetic field.
"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," Moore said in the statement. "With this new understanding of magnetic fields, during future science passes we will begin to create a planet-wide map of Jupiter's [magnetic] variation. It may also have applications for scientists studying Earth's magnetic field, which still contains many mysteries to be solved."
