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The original goal of the team's observing proposal was to determine whether Europa has a thin, extended atmosphere, or exosphere. Using the same observing method that detects atmospheres around planets orbiting other stars, the team realized if there was water vapor venting from Europa's surface, this observation would be an excellent way to see it.
"The atmosphere of an extrasolar planet blocks some of the starlight that is behind it," Sparks explained. "If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter."
In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter. They saw what could be plumes erupting on three of these occasions.
This work provides supporting evidence for water plumes on Europa. In 2012, a team led by Lorenz Roth of the Southwest Research Institute in San Antonio, detected evidence of water vapor erupting from the frigid south polar region of Europa and reaching more than 100 miles (160 kilometers) into space. Although both teams used Hubble's Space Telescope Imaging Spectrograph instrument, each used a totally independent method to arrive at the same conclusion.
"When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it's pretty similar to what Roth and his team found," Sparks said. "The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work."
But as of yet, the two teams have not simultaneously detected the plumes using their independent techniques. Observations thus far have suggested the plumes could be highly variable, meaning that they may sporadically erupt for some time and then die down. For example, observations by Roth's team within a week of one of the detections by Sparks' team failed to detect any plumes.
Above: A comparison of 2014 transit and 2012 Europa aurora observations. The raw transit image, left, has dark fingers or patches of possible absorption in the same place that a different team (led by Lorenz Roth) found auroral emission from hydrogen and oxygen, the dissociation products of water.
If confirmed, Europa would be the second moon in the solar system known to have water vapor plumes. In 2005, NASA's Cassini orbiter detected jets of water vapor and dust spewing off the surface of Saturn's moon Enceladus.
Scientists may use the infrared vision of NASA's James Webb Space Telescope, which is scheduled to launch in 2018, to confirm venting or plume activity on Europa. NASA also is formulating a mission to Europa with a payload that could confirm the presence of plumes and study them from close range during multiple flybys.
"Hubble's unique capabilities enabled it to capture these plumes, once again demonstrating Hubble's ability to make observations it was never designed to make," said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington. "This observation opens up a world of possibilities, and we look forward to future missions — such as the James Webb Space Telescope — to follow up on this exciting discovery."
The work by Sparks and his colleagues will be published in the Sept. 29 issue of the Astrophysical Journal.
Wehaveliftoff
No where near as conclusive as the sulfur fumes first witnessed at Io, Jupiter's moon. Now that was exciting to witness.
Blackarrow
...but potentially FAR more significant!
Robert Pearlman
NASA release
NASA hosts live discussion about Europa findings, potential for life
NASA will host a Science Chat at 1 p.m. EDT Monday, May 14, to discuss the latest analysis of Jupiter's moon Europa and its status as one of the most promising places in the solar system to search for life. The event will air live on NASA Television, Facebook Live, Twitch TV, Ustream, YouTube, Twitter/Periscope and the agency's website.
Europa has long been a high priority for exploration because beneath its icy crust lies a salty, liquid water ocean. NASA's Europa Clipper, targeted to launch in 2022, will be equipped with the instruments necessary to determine whether Europa possesses the ingredients necessary to support life as we know it.
Lori Glaze, acting director of NASA's Planetary Science Division (PSD), and JoAnna Wendel, PSD communications lead, will host the chat. Guests include:
Xianzhe Jia, associate professor in the Department of Climate and Space Sciences and Engineering at the University of Michigan, Ann Arbor
Elizabeth Turtle, research scientist at Johns Hopkins Applied Physics Laboratory in Laurel, Maryland
Margaret Kivelson, professor emerita of Space Physics in the Department of Earth and Space Sciences at the University of California, Los Angeles
The public can send questions on social media by using #AskNASA at any time during the event.
The icy surface of Jupiter's moon, Europa, is thought to lie on top of a global ocean. Signatures in some Hubble Space Telescope images have been associated with putative water plumes rising above Europa's surface providing support for the ocean theory. However, all telescopic detections reported were made at the limit of sensitivity of the data, thereby calling for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from the magnetic field and plasma wave observations acquired on Galileo's closest encounter with the moon. During this flyby, which dropped below 400 km altitude, the magnetometer recorded an approximately 1,000-kilometre-scale field rotation and a decrease of over 200 nT in field magnitude, and the Plasma Wave Spectrometer registered intense localized wave emissions indicative of a brief but substantial increase in plasma density.
We show that the location, duration and variations of the magnetic field and plasma wave measurements are consistent with the interaction of Jupiter's corotating plasma with Europa if a plume with characteristics inferred from Hubble images were erupting from the region of Europa's thermal anomalies. These results provide strong independent evidence of the presence of plumes at Europa.
Robert Pearlman
NASA release
Old Data Reveal New Evidence of Europa Plumes
Scientists re-examining data from an old mission bring new insights to the tantalizing question of whether Jupiter's moon Europa has the ingredients to support life. The data provide independent evidence that the moon's subsurface liquid water reservoir may be venting plumes of water vapor above its icy shell.
Data collected by NASA's Galileo spacecraft in 1997 were put through new and advanced computer models to untangle a mystery -- a brief, localized bend in the magnetic field -- that had gone unexplained until now. Previous ultraviolet images from NASA's Hubble Space Telescope in 2012 suggested the presence of plumes, but this new analysis used data collected much closer to the source and is considered strong, corroborating support for plumes. The findings appear in Monday's issue of the journal Nature Astronomy.
The research was led by Xianzhe Jia, a space physicist at the University of Michigan in Ann Arbor and lead author of the journal article. Jia also is co-investigator for two instruments that will travel aboard Europa Clipper, NASA's upcoming mission to explore the moon's potential habitability.
"The data were there, but we needed sophisticated modeling to make sense of the observation," Jia said.
Jia's team was inspired to dive back into the Galileo data by Melissa McGrath of the SETI Institute in Mountain View, California. A member of the Europa Clipper science team, McGrath delivered a presentation to fellow team scientists, highlighting other Hubble observations of Europa.
"One of the locations she mentioned rang a bell. Galileo actually did a flyby of that location, and it was the closest one we ever had. We realized we had to go back," Jia said. "We needed to see whether there was anything in the data that could tell us whether or not there was a plume."
At the time of the 1997 flyby, about 124 miles (200 kilometers) above Europa's surface, the Galileo team didn't suspect the spacecraft might be grazing a plume erupting from the icy moon. Now, Jia and his team believe, its path was fortuitous.
When they examined the information gathered during that flyby 21 years ago, sure enough, high-resolution magnetometer data showed something strange. Drawing on what scientists learned from exploring plumes on Saturn's moon Enceladus -- that material in plumes becomes ionized and leaves a characteristic blip in the magnetic field -- they knew what to look for. And there it was on Europa –- a brief, localized bend in the magnetic field that had never been explained.
Galileo carried a powerful Plasma Wave Spectrometer (PWS) to measure plasma waves caused by charged particles in gases around Europa's atmosphere. Jia's team pulled that data as well, and it also appeared to back the theory of a plume.
But numbers alone couldn't paint the whole picture. Jia layered the magnetometry and plasma wave signatures into new 3D modeling developed by his team at the University of Michigan, which simulated the interactions of plasma with solar system bodies. The final ingredient was the data from Hubble that suggested dimensions of potential plumes.
The result that emerged, with a simulated plume, was a match to the magnetic field and plasma signatures the team pulled from the Galileo data.
"There now seem to be too many lines of evidence to dismiss plumes at Europa," said Robert Pappalardo, Europa Clipper project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "This result makes the plumes seem to be much more real and, for me, is a tipping point. These are no longer uncertain blips on a faraway image."
The findings are good news for the Europa Clipper mission, which may launch as early as June 2022. From its orbit of Jupiter, Europa Clipper will sail close by the moon in rapid, low-altitude flybys. If plumes are indeed spewing vapor from Europa's ocean or subsurface lakes, Europa Clipper could sample the frozen liquid and dust particles. The mission team is gearing up now to look at potential orbital paths, and the new research will play into those discussions.
"If plumes exist, and we can directly sample what's coming from the interior of Europa, then we can more easily get at whether Europa has the ingredients for life," Pappalardo said. "That's what the mission is after. That's the big picture."
JPL manages the Europa Clipper mission for the agency's Science Mission Directorate.
denali414
WOW! This is really exciting. If there is ocean activity, a very good chance there is life on Europa — it may not be what we expect, but like the deep ocean plumes in the Pacific Ocean, life can and does exist there.
Ironically this would be the perfect mission and one of the first goals for the James Webb to use its infrared aimed at Europa to confirm the plumes.
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