Europe is an ice-covered Jupiter's moon with a global ocean flowing below its surface. NASA is soon planning a mission to look for signs of possible life there.
Now a new finding from ancient data makes this mission even more enticing.
In recent years, the Hubble Space Telescope has discovered what looks like feathers, probably from water vapor that reaches more than 1
The feathers, if they exist, could contain molecules that indicate whether Europe has the building blocks of life.
In a study published in the journal Nature Astronomy on Monday, scientists report a belated discovery that Galileo, a former NASA spacecraft that studied Jupiter, flown more than 20 years ago through one of the European feathers seems to be. And that happened near one of four regions where Hubble Plumes was watching.
"These are too many coincidences that can be dismissed simply because there is nothing" or "we do not understand the data", "said Robert T. Pappalardo, the project scientist for Europa-Clipper NASA 2022 mission. "It seems there is a phenomenon, and springs seem to be consistent."
Galileo, who launched in 1989, came to Jupiter in 1995 and spent nearly eight years studying the planet and its moons until its mission ended with a swan dive into Jupiter in 2003.
During a flyby of Europe on 16 December 1997, Galileo instruments measured a magnetic field momentum and a jump in electron density. At the time, scientists noticed the unusual readings, but they had no explanation.
Then, in 2005, another spaceship passing another planet on another moon made a startling observation. NASA's Cassini spacecraft – which completed its mission in September – found geysers of ice crystals erupting from Enceladus, a small Saturn moon.
Enceladus also has an ocean of liquid water under his ice, as it turns out.
This spurred new curiosity about Europe and whether it could move parts of its ocean into space. The Hubble saw signs of possible plumes in 2012, then again in 2014 and 2016. But at other times, Hubble has seen and seen nothing. This suggests that the feathers are sporadic.
Last year, Melissa McGrath, a senior scientist at the SETI Institute in Mountain View, California, who was not involved in the new study, glanced at some Galileo-led radio experiments that looked at signals between Europe moved back and forth The earth and the spacecraft. The experiments showed that Europe has an atmosphere.
Some of the flyovers indicated a higher density of particles near the surface – possible clouds. Before leaving for a gathering of scientists working on the Clipper mission, McGrath wondered, "Gee, I should really check if any of them agree with any of the claimed feather cloud counters" by Hubble.
One of them actually did.
Margaret G. Kivelson, a professor emeritus of space physics at UCLA, who was the main detector for Galileo's magnetometer, was at McGrath's speech. She remembered the strange magnetic measurements of 1997.
For years she had thought to re-examine the data for signs of feathers, but "there are still other things to do," she said.
Then she did it.
"With the Hubble data in hand," Kivelson said, "we had an idea of how big a plume might make sense, and we could deduce how long Galileo would need to get over a proposed feather.
The three-minute magnetic anomaly seemed to be consistent with the apparent size of the Hubble cloud.
Next, they turned to William S. Kurth, an astronomer at the University of Iowa, who was involved in Galileo's plasma wave experiment that heard radio waves generated by charged particles traveling along magnetic fields around Jupiter and its moons. and tapped. This instrument also noticed a radio wave burst during the flyby – and right in the middle of the magnetic anomaly.
The final piece was a computer model of a pen by Xianzhe Jia, a professor of climate and space sciences and engineering at the University of Michigan, who produced the same effects on the magnetic field and plasma waves.
"It all seemed to hang together," Kivelson said.
The situation was close, though not exactly the same, as the site McGrath reported. But McGrath said the new paper was convincing. "They did the modeling really well and made a strong case," she said.
Also confident is Rep. John Culberson, R-Texas, chairman of the House's subcommittee, which states the budget of NASA. Culberson was an enthusiastic supporter of the Clipper mission and has repeatedly added more money to the project than NASA has requested. He also pushed for a follow-up mission that would land on Europe and hit the ice.
At a Subcommittee meeting last week, Culberson distributed the article to his colleagues that was not publicly available. "It's worth noting that the science journal Nature Astronomy has just reported that the Galileo mission flew across Europe in 1997 through a water flag," he said. "This is how the ocean of Europe discharges directly into space."
The scientists were amused because they were not yet allowed to speak publicly about their results. "That was really funny because we were so careful," said Kivelson. "And suddenly Rep. Culberson throws the paper on the table, very funny."
Astronomers will certainly look at Europe with the Hubble and try to understand how often the feathers erupt.
Pappalardo said that it could be possible to adjust the Europa Clipper trajectory so that at least one of the more than 40 planned fly-bys travels over a potential flag point. But that would have to be balanced against other scientific goals and how much fuel would be needed to hit the orbit of the spaceship.
"Obviously, this is a place we want to live out with the Europa Clipper mission in the future," he said. "I think this will lead to a lively debate at our next science mission meeting."
A European Space Agency spacecraft called Juice or Jupiter Icy Moon's Explorer will also fly from Europe and two other Jupiter satellites, Ganymede and Callisto. It could also start in 2022.