Scientists have made a groundbreaking discovery of a plume of water on Jupiter’s moon Europa, hidden in decades-old data from NASA’s Galileo spacecraft. And it could have important implications in the search for life.
In a paper published in Nature Astronomy, a team led by Xianzhe Jia from the University of Michigan described how they re-analyzed data from the Galileo mission, which orbited Jupiter from 1995 to 2003.
And they found that on December 16, 1997 the spacecraft appears to have flown straight through a plume on Europa, which may have been ejected from a suspected ocean beneath its icy surface. This corroborates with previous findings from the Hubble Space Telescope that suggests Europa is ejecting plumes.
“We deem this as very compelling evidence that Europa does possess plumes,” Jia told IFLScience. “We believe the spacecraft has gone through a plume proper.”
During this flyby (called E12) the spacecraft flew past Europa at an altitude of about 125 miles (200 kilometers). The data shows that two of its instruments measured a spike in the magnetic field and plasma density for about three minutes.
This spike is thought to be consistent with a plume coming from the moon. As the water was ejected out from the surface, it would have droplets and material ranging in size from molecules to dust grains. These become ionized as they travel into space, turning into charged particles known as plasma.
Plasma is also able to affect the magnetic field, meaning that Galileo could make two detections of this incoming plume of material from its two instruments. With a computer simulation, the team was able to show that the spikes they saw were most likely the result of a plume. And they could even work out its size.
“We estimated the size by looking at how long the signal was in the data and knowing the speed of the spacecraft,” said Jia. “It was maybe 1,000 kilometers [620 miles] wide.”
When the detection was first made, scientists had been unsure what they were seeing. It wasn’t until years later that we spotted plumes on Saturn’s moon Enceladus, and Hubble did not spot Europa’s plumes until the 2010s. So such an idea was very new.
“You might say it’s a lack of thinking outside of the box,” William Kurth from the University of Iowa, one of the scientists on Galileo mission and a co-author on this latest paper, told IFLScience. “But on the other hand, had we made a point of going out on a limb, I believe even myself would have thought it was highly speculative.”