A new model shows how brine on Jupiter’s moon Europa can migrate within the icy shell to form pockets of salty water that erupt to the surface when freezing. The findings, which are important for the upcoming Europa Clipper mission, may explain cryovolcanic eruptions across icy bodies in the solar system.
On Jupiter’s icy moon Europa, powerful eruptions may spew into space, raising questions among hopeful astrobiologists on Earth: What would blast out from miles-high plumes? Could they contain signs of extraterrestrial life? And where in Europa would they originate? A new explanation now points to a source closer to the frozen surface than might be expected.
Rather than originating from deep within Europa’s oceans, some eruptions may originate from water pockets embedded in the icy shell itself, according to new evidence from researchers at Stanford University, the University of Arizona, the University of Texas and NASA’s Jet Propulsion Laboratory.
Using images collected by the NASA spacecraft Galileo, the researchers developed a model to explain how a combination of freezing and pressurization could lead to a cryovolcanic eruption, or a burst of water. The results, published today (November 10, 2020) in Geophysical Research Letters, have implications for the habitability of Europa’s underlying ocean – and may explain eruptions on other icy bodies in the solar system.
Harbingers of life?
Scientists have speculated that the vast ocean hidden beneath Europa’s icy crust could contain elements necessary to support life. But short of sending a submersible to the moon to explore, it’s difficult to know for sure. That’s one reason Europa’s plumes have garnered so much interest: If the eruptions are coming from the subsurface ocean, the elements could be more easily detected by a spacecraft like the one planned for NASA’s upcoming Europa Clipper mission.
But if the plumes originate in the moon’s icy shell, they may be less hospitable to life, because it is more difficult to sustain the chemical energy to power life there. In this case, the chances of detecting habitability from space are diminished.
“Understanding where these water plumes are coming from is very important for knowing whether future Europa explorers could have a chance to actually detect life from space without probing Europa’s ocean,” said lead author Gregor Steinbrügge, a postdoctoral researcher at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth).
The researchers focused their analyses on Manannán, an 18-mile-wide crater on Europa that was created by an impact with another celestial object some tens of millions of years ago. Reasoning that such a collision would have generated a tremendous amount of heat, they modeled how melting and subsequent freezing of a water pocket within the icy shell could have caused the water to erupt.
“The comet or asteroid hitting the ice shell was basically a big experiment which we’re using to construct hypotheses to test,” said co-author Don Blankenship, senior research scientist at the University of Texas Institute for Geophysics (UTIG) and principal investigator of the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instrument that will fly on Europa Clipper. “The polar and planetary sciences team at UTIG are all currently dedicated to evaluating the ability of this instrument to test those hypotheses.”
The model indicates that as Europa’s water transformed into ice during the later stages of the impact, pockets of water with increased salinity could be created in the moon’s surface. Furthermore, these salty water pockets can migrate sideways through Europa’s ice shell by melting adjacent regions of less brackish ice, and consequently become even saltier in the process.
“We developed a way that a water pocket can move laterally – and that’s very important,” Steinbrügge said. “It can move along thermal gradients, from cold to warm, and not only in the down direction as pulled by gravity.”
A salty driver
The model predicts that when a migrating brine pocket reached the center of Manannán crater, it became stuck and began freezing, generating pressure that eventually resulted in a plume, estimated to have been over a mile high. The eruption of this plume left a distinguishing mark: a spider-shaped feature on Europa’s surface that was observed by Galileo imaging and incorporated in the researchers’ model.
“Even though plumes generated by brine pocket migration would not provide direct insight into Europa’s ocean, our findings suggest that Europa’s ice shell itself is very dynamic,” said co-lead author Joana Voigt, a graduate research assistant at the University of Arizona, Tucson.
The relatively small size of the plume that would form at Manannán indicates that impact craters probably can’t explain the source of other, larger plumes on Europa that have been hypothesized based on Hubble and Galileo data, the researchers say. But the process modeled for the Manannán eruption could happen on other icy bodies – even without an impact event.
“Brine pocket migration is not uniquely applicable to Europan craters,” Voigt said. “Instead the mechanism might provide explanations on other icy bodies where thermal gradients exist.”
The study also provides estimates of how salty Europa’s frozen surface and ocean may be, which in turn could affect the transparency of its ice shell to radar waves. The calculations, based on imaging from Galileo from 1995 to 1997, show Europa’s ocean may be about one-fifth as salty as Earth’s ocean – a factor that will improve the capacity for the Europa Clipper mission’s radar sounder to collect data from its interior.
The findings may be discouraging to astrobiologists hoping Europa’s erupting plumes might contain clues about the internal ocean’s capacity to support life, given the implication that plumes do not have to connect to Europa’s ocean. However, the new model offers insights toward untangling Europa’s complex surface features, which are subject to hydrological processes, the pull of Jupiter’s gravity and hidden tectonic forces within the icy moon.
“This makes the shallow subsurface – the ice shell itself – a much more exciting place to think about,” said co-author Dustin Schroeder, an assistant professor of geophysics at Stanford. “It opens up a whole new way of thinking about what’s happening with water near the surface.”
Reference: “Brine Migration and Impact‐Induced Cryovolcanism on Europa” by G. Steinbrügge, J. R. C. Voigt, N. S. Wolfenbarger, C. W. Hamilton, K. M. Soderlund, D. A. Young, D. D. Blankenship, S. D. Vance and D. M. Schroeder, 5 November 2020, Geophysical Research Letters.
Schroeder is also an assistant professor, by courtesy, of electrical engineering and a center fellow, by courtesy, at the Stanford Woods Institute for the Environment. Co-authors include Krista Soderlund, Natalie Wolfenbarger and Duncan Young from the University of Texas at Austin; Christopher Hamilton from the University of Arizona, Tucson; and Steven Vance from NASA’s Jet Propulsion Laboratory.
The research was supported by the G. Unger Vetlesen Foundation. A portion of the work was carried out by the Jet Propulsion Laboratory, Caltech, under a contract with NASA.
I love space nd science aliens
There was talk,many years ago, about sending a craft off to Europa. Once it was to land it was then to bore down through its icy crust, release another probe which was then to swim down to the oceans surface in the hope of finding volcanic vents to find life as is the case on earth’s oceans floors. Has this idea been scrapped as I’ve been waiting a long time for this?
Jupiter’s job, as with all the other planets, is to support life to continue here on Earth.
All with a specific task to stabilize things here, for life to continue.
For instance, Jupiter sweeps the area clean, and literally takes the ‘hit’ for us. Heard of Shoemaker Levy?
If Jupiter were to be any closer, its gravitational pull would tear us apart. Any farther out, and asteroids would destroy us.
Yes, ALL of the planets are rightly placed, and have a specific ‘job’ to protect life here on Earth.
Even the Moon is necessary, being precisely where it is located, and the size that it is.
What IS this thing called ‘life’?
How does it spring forth from ‘inanimate matter’?
Doesn’t life always need to come from a previous lifeform?
And most importantly, can consciousness and life ever be separated?
Yet scientists desperately want the Star Trek universe to be true. In fact, this article supports this. (ie, It’s only a matter of time before e.t. life is found.)
Let man search the cosmos, and he’ll seek in vain, because that’s not the way life works. Though, it’s quite entertaining, to say the least.
The latest incorrect assumption was life in the clouds of Venus, with the discovery of PH3.
Though, I believe that there’s only one consciousness of being, YOU, originating from a vastly greater dimension, pushed -out here onto the ‘screen’ of 3D space, for only a short span of time.
I’m sure that you are familiar with the story of ‘Flatland’? 2D people trying to explain the 3D world?
This 3D world IS a ‘Flatland’ to a greater dimension, where consciousness and life originates.
And, as amazing as our world and universe is, it is but a mere shadow being cast from this greater dimension.
What are we here to do and to cultivate? What is more important to focus upon?
Whether life exists ‘out there’ somewhere in outer space? Or, to start taking care of the precious, and unique forms of life here on this very, very rare Earth?
We’ve all grown up now, many generations deep, with the indoctrination of a ‘Star Trek’ mentality, a universe that’s teeming with life.
Though I believe just the opposite is true. And the reason for this is WHY we are here on this sphere to begin with? What is the point of our existence?
Is this truly our ‘home’, or is this merely a ‘schoolhouse’ of experience for only a brief period?
Yes, life on this planet is a very rare thing in the cosmos. I know, it doesn’t make any sense why it shouldn’t be everywhere in this vast universe.
Though, to this day, Drake and Fermi still do not play well together
In ALL of these decades of SETI, not one speck of life has ever been found elsewhere except upon Earth.
We need to re-evaluate what this mystery called life really is, and not just jump over this mystery happening here on Earth, and ASSUME that it just has to be happening everywhere.
All the decades of searching for e.t. points to the distinct possiblity that life is truly a very rare thing in the cosmos, as in nonexistent.