Officially, the researchers-Xianzhe Jia, Margaret Kivelson, Krishan Khurana, and William Kurth-report that instruments onboard the Galileo space probe detected intense, localized changes in the magnetic fields and plasma density of Europa's atmosphere as the probe flew 400 km above the surface of the moon. If enough evidence of water plumes is found, NASA (and other space agencies, we must assume) will investigate further, maybe someday bringing back samples.
"It's worth noting that the scientific journal Nature Astronomy just reported that the Galileo mission, back in 1997, flew through a water plume on Europa 1,000 kilometers thick", Culberson said during an appropriations subcommittee markup in the House. That Hubble data, however, wasn't definitive proof of erupting plumes because it's such a hard observation to make from Earth's orbit. So a team of USA astronomers went back and took a second look at data collected by the Galileo spacecraft during its eight-year stay in the Jovian system. To study the makeup of the water on Europa, scientists would only need to perform flybys with spacecraft going through the plumes instead of landing on the moon.
"When we took a detailed look at the Galileo data obtained more than 20 years ago, we saw those peculiar signals in both the magnetic field and plasma wave data that no one seemed to have explained before", Jia said.
To study the plumes, the probe will not need to pass directly through them.
'These results provide strong independent evidence of the presence of plumes at Europa, ' researchers wrote.
"The Hubble observations are circumstantial evidence that plumes could have been present more recently, starting in 2012".
The proofs of the existence of water plumes on Europa, which are emerging from the surface of the moon, have been gathering for a number of years. This indicates the existence of periodic jets of water emanating from the moon's interior. The Cassini mission caught sight of plumes erupting from Saturn's moon Enceladus.
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Many experts believe the hidden ocean surrounding Europa, warmed by powerful tidal forces caused by Jupiter's gravity, may have conditions favourable for life. This led the scientists to conclude that Hubble had indeed seen plumes on Europa, and Galileo must have flown near or through one.
"To detect a plume for certain, we'll have to return to the Jupiter system, and NASA's Europa Clipper spacecraft, now in development, will do just that", Phillips said.
Sampling the water possibly eruption from Europa could have huge implications for our understanding of the world.
Researchers have long believed that Europa is home to a vast saltwater ocean, trapped beneath a thick crust of ice, making the moon potentially habitable for life and a focus of upcoming robotic exploration.
But sending a robot craft to land on Europa and drill through its surface would be a much more costly and complicated endeavour than, say, flying through a plume of water ejected from the moon's innards, and measuring its composition.
"It's unlikely that plumes, if they exist, come directly from a subsurface ocean layer, since the surface ice layer is thought to be kilometers thick".