Scientists thought Jupiter's moon Europa was ejecting water. Now not so sure

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https://www.space.com/astronomy/solar-system/hubble-telescope-watched-jupiters-moon-europa-for-14-years-and-now-scientists-arent-sure-if-its-ejecting-water-after-all

Scientists thought Jupiter's moon Europa was ejecting water. Now they're 
not so sure
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By Robert Lea published 4 hours ago
"The evidence for water vapor plumes on Europa isn’t as strong as we 
first understood it."

(Main) Jupiter's moon Europa and (Inset) Hubble Space Telescope
(Main) Jupiter's moon Europa and (Inset) Hubble Space Telescope (Image 
credit: NASA)

Astronomers have studied 14 years of Hubble Space Telescope observations 
of Jupiter's icy moon Europa, and now suspect that its infamous water 
vapor eruptions may not exist as was previously thought

Europa has long been a hot target for scientists aiming to investigate 
the habitability of nearby worlds and the possible existence of life 
elsewhere in the solar system. That is because this Jovian moon is 
thought to host a global subsurface ocean that possibly harbors some of 
the essential elements for life under its thick and icy shell, including 
complex organic chemicals and water.

The faint and difficult-to-detect plumes were previously thought to 
originate from the vast global saltwater ocean lurking beneath the icy 
shell of Europa. This material is thought to erupt from cracks in the 
icy shell of the moon. Now, previous evidence of the existence of these 
plumes has been called into question by the very scientists who 
initially proposed them.

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"The evidence for water vapor plumes on Europa isn’t as strong as we 
first understood it," team member Kurt Retherford of the Southwest 
Research Institute (SwRI) said in a statement. Retherford was part of a 
team that in 2014 suggested the existence of these European water 
plumes, but he and his colleagues now reconsider this conclusion.

Another look at Europa
To reconsider the existence of Europa's water plume eruptions, 
Retherford and colleagues looked at 14 years of data regarding Europa 
collected by Hubble using its HST/STIS instrument (Hubble Space 
Telescope’s Space Telescope Imaging Spectrograph). In particular, they 
honed in on a specific wavelength of ultraviolet light called 
Lyman-alpha emissions, which is emitted and scattered by hydrogen atoms.

Retherford and team had been detecting Lyman-alpha emissions from Europa 
between 2012 and 2014, but this investigation was pushing Hubble to its 
very limits.

"One of the difficulties in interpreting the data back then was 
determining where to place Europa within its context," Retherford 
explained. "The way Hubble works left some uncertainty in terms of 
placement relative to the center of the image. If Europa’s placement was 
off even just by a pixel or two, it could affect how the data gets 
interpreted.”

The existence of water vapor plumes on Jupiter’s moon Europa 
initially reported based in Hubble observations from 2012 are now in doubt

The existence of water vapor plumes on Jupiter’s moon Europa initially 
reported based in Hubble observations from 2012 are now in doubt (Image 
credit: NASA)
The team feared that the detection of water vapor plumes from Europa may 
have been the result of "noise" in their data.

"Our reanalysis took our original 99.9% confidence in the plumes’ 
existence and reduced it to less than 90% confidence," team leader 
Lorenz Roth of the KTH Royal Institute of Technology, Sweden, said. 
"That's simply not enough evidence to support the certainty of claims we 
made at the time."

The team still can't confidently rule out the existence of Europa's 
water vapor, especially as similar plumes have been more confidently 
detected on Saturn's icy moon of Enceladus, and sulfur dioxide eruptions 
have been detected from Europa's fellow Jovian moon of Io, the most 
volcanic body in the entire solar system.

The question of the existence of these water plumes and the salty global 
ocean of Europa may finally be settled in 2030 when NASA's Europa 
Clipper mission arrives in the Jovian system.

The team's research was published on May 5 in the journal Astronomy & 
Astrophysics.

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