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A New Source for Plumes on Europa

How salty should we expect the ice on Europa’s surface to be? It would be helpful to know, because the salinity of the surface will be a factor in how transparent the ice shell is to radar waves. Europa Clipper will fly with an instrument called REASON — Radar for Europa Assessment and Sounding: Ocean to Near-surface — which will be investigating both the surface ice and the ocean beneath. Recent research, in which its principal investigator, Don Blankenship (University of Texas), is involved is offering insights into the salinity of the ice.

Here’s a bit of background on REASON from a NASA page on Europa Clipper:

Depending on their wavelength, radio waves can either bounce off or penetrate different materials. REASON will use high frequency (HF) and very high frequency (VHF) radio signals to penetrate up to 18 miles (30 kilometers) into Europa’s ice to look for the moon’s suspected ocean, measure ice thickness, and better understand the icy shell’s structure. The instrument will also study the elevation, composition, and roughness of Europa’s surface, and will search Europa’s upper atmosphere for signs of plume activity.

Image: Europa Clipper, scheduled for launch in 2024. Credit: NASA/JPL-Caltech.

So plumes are in play for Europa Clipper, and the new research finds evidence of a process that can produce them. The paper in Geophysical Research Letters focuses on what the authors call brine migration, in which small pockets of salty water migrate within the ice to warmer icy areas. We get into questions of salinity in this work because migration of icy brines, analyzed here through study of the impact crater Manannán, may have resulted in the creation of a plume. Imaging data from the Galileo mission allowed the team to study the resulting surface feature and to calculate that Europa’s ocean is about a fifth as salty as Earth’s.

But let’s back up to that plume. If eruptions from the ocean below periodically break through the ice, we might have a way to sample ocean materials without ever trying to drill through the surface shell. The new work, led by Gregor Steinbrügge (Stanford University) homes in on Manannán, a 30-kilometer wide crater on Europa that is the result of an impact some tens of millions of years ago. The paper models the melting and refreezing of water following the event. And it suggests that not all plumes carry materials from the ocean below.

Manannán is located on Europa’s trailing hemisphere at 3°0’N and 120°50’E. The crater was imaged by the Galileo spacecraft’s Near-Infrared Mapping Spectrometer. Subsequent geological mapping of Manannán has shown what appear to be impact melt materials filling the crater floor, along with ejecta deposits that would have been brought up from below at the time of impact.

According to the researchers, as water transformed back into ice following the impact, pockets of water with higher salt content were created in the surface, migrating sideways through the shell by melting adjacent areas of less salty ice. “We developed a way that a water pocket can move laterally – and that’s very important,” says Steinbrügge. “It can move along thermal gradients, from cold to warm, and not only in the down direction as pulled by gravity.”

Image: This illustration of Jupiter’s icy moon Europa depicts a cryovolcanic eruption in which brine from within the icy shell could blast into space. A new model proposing this process may also shed light on plumes on other icy bodies. Credit: Justice Wainwright.

Pockets of brine moving about within the surface become saltier as they move through less salty water around them and eventually erupt, according to this model, which shows freezing and pressurization as the factors leading to a cryovolcanic event. At Manannán crater, a migrating brine pocket finally freezing at the center generated a plume estimated to be 1-2 kilometers high, leaving a surface feature, roughly spider-like in shape, that turned up in the Galileo data. The spider-shaped fractures consist of 17 segments, surrounded by a series of concentric faults. This would have been a relatively small plume, and the Manannán findings do not explain what may be larger plumes hypothesized based on Hubble and Galileo data.

Image: The ‘spider’ feature within Manannán impact crater. Credit: NASA.

The point is that brine pocket migration is a surface phenomenon that can generate plumes, implying that such plumes do not require a connection with the ocean beneath. Whether there are other, larger plumes that do make such connections has not yet been determined.

Oceanic origin or not, all of this makes Europa’s surface an even more dynamic place than we’ve been considering, while somewhat tempering our expectations for astrobiology in plume activity even as we continue to observe the moon for future, perhaps much larger plumes. The team’s modeling of how melting and subsequent freezing of a water pocket within the icy shell would produce an eruption should have implications for other icy bodies within the Solar System. Robert Pappalardo (JPL) is a project scientist on the Europa Clipper mission:

“The work is exciting, because it supports the growing body of research showing there could be multiple kinds of plumes on Europa. Understanding plumes and their possible sources strongly contributes to Europa Clipper’s goal to investigate Europa’s habitability.”

The paper is Steinbrügge et al. ,”Brine Migration and Impact‐Induced Cryovolcanism on Europa,” Geophysical Research Letters 5 November 2020 (abstract).


Comments on this entry are closed.

  • Alex Tolley November 17, 2020, 12:24

    While this may complicate the search for life, I would have thought that a plume only 1-2 kilometers in height might be too low to sample by a probe. This would self-eliminate such plumes in favor of those whose source is the subsurface ocean.

    Given the nature of these surface melts, would they be bright areas for the “night glow” analysis in the earlier post: Europa: Night-time Glow a New Tool for Analysis.

    The opening paragraph indicated that salinity was a factor in how deep ground-penetrating radar could go. I don’t see any further discussion about this. Do local differences in brine concentration affect the depth achieved? Is the ice crust so thick that there is no likely reflection from the ocean-ice boundary, leaving the depth at which the ocean starts undetermined? Would the radar detect liquid pockets on the surface and at depths within the crust?

    As with Mars, will we need a lander to look for life on Europa?

  • Ashley Baldwin November 17, 2020, 14:03

    Let’s hope Juno gets its four year mission extension granted in December. To assess the three inner Galilean moons. With one of its four proposed observation encounters less than 200 miles from Europa , it’s Microwave Radiometer ( effectively a less sensitive version of Clipper’s REASON instrument ) might be able to penetrate Europa’s ice to sufficient depth to confirm or repudiate this theory . Certainly to spot the crustal ‘puddles’ posited. Any plume activity could be assessed by its Clipper analogue ultraviolet and infrared imaging spectrographs . Relatively crude in comparison to Clipper but hugely superior to both Voyager and Galileo ( 2010 vs 1970s) , we might just get an early insight ( by late 2022) .

  • Robin Datta November 18, 2020, 0:04

    Horizontal passageways for water could communicate with deepor water and may thus carry organisms therefrom.

  • Mike Serfas November 22, 2020, 10:46

    If thoroughly mapped and drilled into with great caution (and sturdy insulated casings), these migrating pockets sound like an immensely valuable resource for potential colonists. If they can send a plume of brine 1-2km into space against 13% g, that is roughly four times the potential energy of Niagara Falls for hydroelectric power production. Released gently to the surface, the brine then becomes a geothermal resource, and it will leave behind a mineral resource after the water is extracted for human use or frozen as pure ice for construction.

  • Ljk December 22, 2020, 23:36

    An underwater rover to explore Europa’s global ocean…


  • ljk January 9, 2021, 16:09

    How future spacecraft might handle tricky landings on Venus or Europa

    Fan-powered descents and nimble landing legs are just two ideas for touching down safely


  • ljk January 9, 2021, 16:11

    05 Jan 2021 | 21:52 GMT

    Robots Made of Ice Could Build and Repair Themselves on Other Planets

    Ice is all over the solar system, and exploration robots could use it as a structural material

    By Evan Ackerman


  • ljk January 29, 2021, 16:22

    So who and what will send Europa Clipper to Jupiter?


  • ljk February 11, 2021, 15:16

    Review: The Mission

    Getting approval for a mission to Jupiter’s icy moon Europa involved a unique set of political, technical, and bureaucratic challenges. Jeff Foust reviews a book that examines how the advocates for Europa Clipper overcame the many obstacles in their path.

    Monday, February 8, 2021


  • ljk February 12, 2021, 17:08

    NASA to use commercial launch vehicle for Europa Clipper

    by Jeff Foust — February 10, 2021


  • ljk February 16, 2021, 11:57

    Does this discovery hold promise for life on Europa, Enceladus, and other such icy alien worlds?


  • ljk March 11, 2021, 14:00

    So apparently the very bottom of Europa’s global ocean of liquid water at a suspected depth of 60 miles has a surrounding water pressure of no more than that found in the Mariana Trench on Earth, thanks to the alien moon being about the same size as our Moon.

    As we have now built a robotic submersible that can “swim” at such depths, we should be able to explore Europa’s distant ocean all the way down, especially since the technologies will only get better by the time we actually get a vessel there.


  • ljk April 8, 2021, 10:42


    Probing for Life in the Icy Crusts of Ocean Worlds

    Source: NASA

    Posted April 7, 2021 11:09 PM

    (A–C) Views of the instrument drill combination. (A) Schematic drawing of the Honeybee Planetary Deep Drill and WATSON DUV mapping spectrometer. Mannequin for scale. (B) Image of actual constructed drill and stand. (C) Image of WATSON DUV mapping spectrometer. Left side of image shows uncovered components, and right image shows instrument in down-borehole configuration with the protective tube in place. The optical window can be seen at center right. DUV, deep-ultraviolet; WATSON, Wireline Analysis Tool for the Subsurface Observation of Northern ice sheets. Color images are available online.

    A technique for scanning Mars rocks for microscopic fossils of ancient life is also being developed to hunt for microbes in the deep ice of Enceladus, Titan, and Europa.

    Long before NASA’s Perseverance rover touched down on the Red Planet on Feb. 18, one of its highest-level mission goals was already established: to seek out signs of ancient life on the Martian surface. In fact, the techniques used by one of the science instruments aboard the rover could have applications on Saturn’s moons Enceladus and Titan as well Jupiter’s moon Europa.

    “Perseverance is going to look for a shopping list of minerals, organics, and other chemical compounds that may reveal microbial life once thrived on Mars,” said Luther Beegle, principal investigator for Mars 2020’s Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) instrument. “But the technology behind SHERLOC that will look for past life in Martian rocks is highly adaptive and can also be used to seek out living microbes and the chemical building blocks for life in the deep ice of the moons of Saturn and Jupiter.”

    Enceladus, Europa, and even the hazy moon Titan are thought to hide vast oceans of liquid water containing chemical compounds associated with biological processes below their thick icy exteriors – very different environments from modern Mars. If microbial life exists in those waters, scientists may be able to find evidence of it in the ice as well. But how to find that evidence if it’s locked deep in the ice?

    Enter WATSON. Short for Wireline Analysis Tool for the Subsurface Observation of Northern ice sheets, the 3.9-foot-long (1.2-meter-long) long tube-like prototype is undergoing development at NASA’s Jet Propulsion Laboratory in Southern California. It has been coupled to Honeybee Robotics’ Planetary Deep Drill, and this combination was successfully tested in the extreme cold of Greenland’s ice.

    A smaller version of WATSON could one day ride aboard a future robotic mission to explore the habitability potential of one of these enigmatic moons. The instrument would scan into the ice in search of biosignatures – organic molecules created by biological processes. Should it spot any, a future version of WATSON, with the additional capability of collecting ice from the borehole wall, could then gather samples for further study.

    By using deep-ultraviolet laser Raman spectroscopy to analyze the materials where they are found, rather than immediately retrieving ice samples and then studying them on the moon’s surface, the instrument would provide scientists additional information about these samples by studying where they are in the context of their environment.

    “It would be great if we first studied what these samples actually looked like in their natural environment before scooping and blending them up into a slurry for testing,” said Mike Malaska, an astrobiologist at JPL and the lead scientist for WATSON. “That’s why we’re developing this non-invasive instrument for use in icy environments: to get a deep look into the ice and identify clusters of organic compounds – maybe even microbes – so they can be studied before we analyze them further and lose their native context or modifiy their structure.”

    Although WATSON uses the same technique as Perseverance’s SHERLOC, there are differences. For one, SHERLOC will analyze Martian rock and sediment to hunt for signs of past microbial life that can be collected and returned to Earth by future missions for deeper study. And SHERLOC doesn’t drill holes. A separate tool does that.

    But both rely on a deep-ultraviolet laser and spectrometer, and where the WATSON ice instrument has an imager to observe the texture and particulates in the ice wall, Perseverance’s SHERLOC is paired with a high-resolution camera to take close-up pictures of rock textures to support its observations. That camera happens to share the same name as the ice-exploring prototype: WATSON. In this case, though, the acronym stands for Wide Angle Topographic Sensor for Operations and eNgineering. (After all, any instrument with a name inspired to the famous fictional detective Sherlock Holmes is bound to inspire references to his partner.)

    Enceladus on Earth

    Just as SHERLOC underwent extensive testing on Earth before going to Mars, so must WATSON before it is sent to the outer solar system. To see how the instrument might perform in the icy crust of Enceladus and the moon’s extremely low temperatures, the WATSON team chose Greenland as an “Earth analog” for field tests of the prototype during a 2019 campaign.

    Earth analogs share similar characteristics with other locations in our solar system. In the case of Greenland, the environment near the middle of the island’s ice sheet and away from the coast approximates the surface of Enceladus where ocean materials erupt from the small moon’s prolific vents and rain down. The mangled ice at the edge of Greenland’s glaciers near the coast, meanwhile, can serve as an analog for Europa’s buckled deep icy crust.

    WATSON produced this fluorescence map of a borehole at a depth of 307.7 feet (93.8 meters) in Greenland’s ice. The left panel shows nebulous blobs of biosignatures, and the right panel shows a colorized version, grouping together similar organic chemicals. Credit: NASA/JPL-Caltech

    During the campaign to explore an existing borehole near Summit Station, a high-elevation remote observing station in Greenland, the instrument was put through its paces. As it descended more than 330 feet (100 meters), WATSON used its UV laser to illuminate the walls of the ice, causing some molecules to glow. The spectrometer then measured their faint glow to give the team insight into their structure and composition.

    While finding biosignatures in Greenland’s icepack didn’t come as a surprise – the tests were on Earth, after all – mapping their distribution along the walls of the deep borehole raised new questions about how these features got where they are. The team discovered that microbes deep in the ice tend to clump together in blobs, not in layers like they originally expected.

    “We created maps as WATSON scanned the sides of the borehole and the clustering hotspots of blues greens and reds – all representing different kinds of organic material,” said Malaska. “And what was interesting to me was that the distribution of these hotspots was pretty much the same everywhere we looked: No matter if the map was created at 10 or 100 meters [33 or 330 feet] in depth, these compact little blobs were there.”

    By measuring the spectral signatures of these hotspots, the team identified colors consistent with aromatic hydrocarbons (some that may originate from air pollution), lignins (compounds that help build cell walls in plants), and other biologically-produced materials (such as complex organic acids also found in soils). In addition, the instrument recorded signatures similar to the glow produced by clusters of microbes.

    There’s more testing to be done – ideally, in other Earth analogs that approximate the conditions of other icy moons – but the team was encouraged by how sensitive WATSON was to such a wide variety of biosignatures. This high sensitivity would be useful on missions to ocean worlds, where the distribution and density of any potential biosignatures are unknown, said Rohit Bhartia, principal investigator for WATSON and deputy principal investigator for SHERLOC, of Photon Systems in Covina, California. “If we were to collect a random sample, we are likely to miss something very interesting, but through our first field tests, we’re able to better understand the distribution of organics and microbes in terrestrial ice that could help us when drilling into the crust of Enceladus.”

    The results of the field test were published in the journal Astrobiology in Fall 2020 and presented at the American Geophysical Union Fall Meeting 2020 on Dec. 11.


  • ljk April 12, 2021, 15:12

    “The Mission: A True Story” By David W. Brown: A Review

    By Keith Cowing

    Posted April 11, 2021 12:18 PM

    To most people outside of NASA, a space mission that is making the news often appears out of nowhere. Sometimes there may be a little news when it is launched and maybe some tidbits along the way.

    Otherwise, when it does something cool – like land on a planet or sends back pretty pictures, you hear about it albeit with no back story. For a moment NASA gets a sugar high and then … nothing – unless the mission makes a big discovery down the road.

    Yes, NASA puts out newsy things with factoids and status reports, but for most people, these missions just seem to happen. But where did the mission come from, people may wonder. Whose idea was it? Who are those people jumping up and down in the control room? Were there other ways to do the mission? Did someone want to go somewhere else instead? Did everyone agree or were there arguments? And by the way, where did that mission’s name come from anyway?

    “The Mission” by David W. Brown takes a rather unorthodox look into the backstory of space missions by focusing on one in particular: the mission currently known as Europa Clipper. Brown documents how this mission came to be, the iterations and name changes it went through, the internal gyrations among program managers, budgeteers, scientists, and politicians, but most importantly, the people. Yes, while the spacecraft are usually the stars of the show, this expensive, shiny hardware is simply a reflection of a team of humans putting their mind toward a distant task – while swatting off other humans who would seek to deter them from their task.

    Full review here:


  • ljk May 14, 2021, 16:05
  • ljk May 26, 2021, 10:09

    Europa could have active underwater volcanoes:


    Every bit helps.