Jupiter's Moon Ganymede Is Pounded by Plasma Rain, Scientists Discover From 20-Year-Old Data

Jupiter's largest moon, Ganymede, knocked scientists' socks off in 1996 when astronomers realized it is the only moon that creates its own magnetic field.

Now scientists have brushed off more data collected during that era to realize something even more incredible about the moon: It is bombarded by a rain of plasma, or highly charged particles, according to a new paper published in the journal Geophysical Research Letters.

“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,” lead author Glyn Collinson, a scientist affiliated with NASA, said in a press release. “We found there’s a whole piece no one knew about.”

Read more: Earth's Magnetic Field Probably Won't Flip After All, New Study Claims

The newly rediscovered information came from a spacecraft called Galileo, which launched in 1989, flew past Venus and two asteroids, then spent its main mission studying Jupiter and its moons until 2003. But not all of the spacecraft's data was analyzed. So on a whim, a team of scientists decided to look back at what the mission gathered about Ganymede.

Ganymede is the single largest moon in our solar system, and scientists think that it may have a giant liquid ocean sloshing around beneath its surface—like the more famous Europa and Enceladus—just the sort of place where extraterrestrial life could be hiding out.

05_01_ganymede_galileo_jupiter Jupiter's largest moon, Ganymede, as seen in January 1999 by the Galileo spacecraft. The moon, which creates its own magnetic field, is bombarded by a rain of plasma. NASA via Reuters

Plus there's the magnetic field, which is intriguing because Earth's equivalent plays a crucial role in making the planet comfortable for life by shielding the surface from plasma released by the sun.

But the story is more complicated at Ganymede, where the magnetic field is influenced by its equivalent around Jupiter. The new finding pinpointed plasma being shared between the two magnetic fields, as well as the rain of plasma falling on the moon and shooting plasma particles off its surface.

But the real takeaway here isn't discovering new information buried in old Galileo data: it's actually the hope that there are other secrets left to be uncovered in data that already exists here on Earth.

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