The magnetic field around Jupiter's moon Ganymede makes it unlike any other in the solar system shows newly analyzed data from NASA's Galileo spacecraft's first flyby of the moon two decades ago.
NASA's Galileo spacecraft spent eight years orbiting Jupiter. During that time, the hearty spacecraft -- slightly larger than a full-grown giraffe -- sent back spates of discoveries on the gas giant's moons, including the observation of a magnetic environment around Ganymede that was distinct from Jupiter's own magnetic field.
The mission ended in 2003, but newly resurrected data from Galileo's first flyby of Ganymede, detailed in the journal Geophysical Research Letters, offered new insights about the moon's environment.
"We are now coming back over 20 years later to take a new look at some of the data that was never published and finish the story," said study lead author Glyn Collinson from NASA's Goddard Space Flight Center in Greenbelt, Maryland.
"We found there's a whole piece no one knew about," Collinson said.
In 1996, shortly after arriving at Jupiter, Galileo made a surprising discovery: Ganymede had its own magnetic field.
While most planets in our solar system, including Earth, have magnetic environments -- known as magnetospheres -- no one expected a moon to have one.
Between 1996 and 2000, Galileo made six targeted flybys of Ganymede, with multiple instruments collecting data on the moon's magnetosphere.
The new results reveal interesting details about the magnetosphere's unique structure.
The results showed a stormy scene. Particles blasted off the moon's icy surface as a result of incoming plasma rain, and strong flows of plasma pushed between Jupiter and Ganymede due to an explosive magnetic event occurring between the two bodies' magnetic environments.
Scientists think these observations could be key to unlocking the secrets of the moon, such as why Ganymede's auroras are so bright.
"There are these particles flying out from the polar regions, and they can tell us something about Ganymede's atmosphere, which is very thin," said Bill Paterson, a co-author of the study at NASA Goddard who served on the Galileo Plasma Science (PLS) team during the mission.
"It can also tell us about how Ganymede's auroras form," Paterson added.