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This artist’s conception of the icy moon of Jupiter, Europa, shows a supposed cryovolcanic eruption, in which the salty water from within the icy layer breaks into space. A new model of this process in Europe may also explain the feathers in other icy bodies. Credit: Judge Blaine Wainwright
A new model shows how the brine JupiterEuropa, the moon of Europa, can migrate within the icy layer to form pockets of salty water that rise to the surface when frozen. The findings, which are important for the upcoming Europa Clipper mission, may explain cryovolcanic eruptions on icy bodies in the solar system.
On Jupiter’s icy moon Europa, powerful eruptions can be thrown into space, raising questions among hopeful astrobiologists on Earth: What would burst from columns miles high? Could they contain signs of extraterrestrial life? And where would they originate in Europe? A new explanation now points to a source closer to the frozen surface than might be expected.
Rather than originating deep in Europe’s oceans, some eruptions may originate from pockets of water embedded in the ice sheet itself, according to new evidence from researchers at Stanford University, the University of Arizona, the University of Texas and POTJet Propulsion Laboratory.
Using images collected by NASA’s spacecraft Galileo, the researchers developed a model to explain how a combination of freezing and pressurization could trigger a cryovolcanic eruption or a water explosion. 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.
Heralds of life?
Scientists have speculated that the vast ocean hidden beneath Europa’s icy crust could contain elements necessary to support life. But aside from sending a submersible to the moon to explore, it’s hard to know for sure. That’s one reason Europa plumes have sparked 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 columns originate in the icy layer of the moon, they can be less hospitable to life, because it is more difficult to maintain the chemical energy to fuel life there. In this case, the chances of detecting habitability from space are reduced.
“Understanding where these plumes of water are coming from is very important to knowing whether future explorers of Europa might have a chance to actually detect life from space without probing Europa’s ocean,” said lead author Gregor Steinbrügge, a postdoctoral researcher at the Stanford School of Earth Energy. And Environmental Sciences (Stanford Earth).
The researchers focused their analyzes on Manannán, a 29-mile-wide crater in 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 an enormous amount of heat, they modeled how the melting and subsequent freezing of a pocket of water within the icy layer could have caused the water to explode.
“The comet or asteroid that hit the ice sheet was basically a grand experiment that we are using to build hypotheses to test,” said co-author Don Blankenship, senior research scientist at the University of Texas Institute of Geophysics (UTIG) and researcher. Radar main for Europe Assessment and Sounding: Ocean to Near-surface (REASON) instrument that will fly in Europa Clipper. “The UTIG Polar and Planetary Sciences team is currently engaged in evaluating the ability of this instrument to test these hypotheses.”
The model indicates that as Europa’s water turned into ice during the later stages of the impact, pockets of water with higher salinity could be created on the moon’s surface. In addition, these pockets of salt water can migrate laterally through the Europa ice sheet by melting adjacent regions of less brackish ice and consequently becoming even more salty in the process.
“We developed a way that a bag of water can move laterally, and that is very important,” said Steinbrügge. “It can move along thermal gradients, from cold to warm, and not just in the downward direction pulled by gravity.”
A salty conductor
The model predicts that when a bag of migrating brine reached the center of Manannán crater, it got stuck and began to freeze, generating pressure that eventually resulted in a plume, estimated to be over a mile high. The eruption of this column left a distinctive mark: a spider-shaped feature on the surface of Europa that was observed by Galileo images and incorporated into the researchers’ model.
“Although the columns generated by the migration of the brine pockets would not provide a direct view of Europa’s ocean, our findings suggest that the Europa ice sheet itself is very dynamic,” said co-lead author Joana Voigt, research assistant. graduated from the University of Arizona, Tucson. .
The relatively small size of the column that would form at Manannán indicates that the impact craters probably cannot explain the source of other larger columns in Europa that have been hypothesized based on Hubble Y Galileo data, say the researchers. But the process modeled for the Manannán eruption could occur on other icy bodies, even without an impact event.
“The migration of the brine pockets does not apply only to the craters of Europan,” said Voigt. “Instead, the mechanism could provide explanations for other icy bodies where there are thermal gradients.”
The study also provides estimates of how salty Europa’s icy surface and ocean can be, which in turn could affect the transparency of its ice sheet to radar waves. The calculations, based on images of Galileo From 1995 to 1997, they show that Europa’s ocean may be about a fifth saltier than Earth’s ocean, a factor that will improve the ability of the Europa Clipper mission’s radar probe to collect data from its interior.
The findings may be discouraging for astrobiologists who hope that the erupting plumes of Europa may hold clues to the inner ocean’s ability to support life, given the implication that the plumes do not have to connect to the ocean of Europa. However, the new model offers information to unravel the complex features of Europa’s surface, which are subject to hydrological processes, the pull of Jupiter’s gravity, and the tectonic forces hidden within the icy moon.
“This makes the shallow subsurface, the ice sheet itself, a much more exciting place to think,” said co-author Dustin Schroeder, assistant professor of geophysics at Stanford. “It opens up a whole new way of thinking about what is happening to water near the surface.”
Reference: “Brine Migration and Impact-Induced Cryovolcanism on Europe” by G. Steinbrügge, JRC Voigt, NS Wolfenbarger, CW Hamilton, KM Soderlund, DA Young, DD Blankenship, SD Vance and DM Schroeder, November 5, 2020, Geophysical Research Letters.
DOI: 10.1029 / 2020GL090797
Schroeder is also a courtesy assistant professor of electrical engineering and a courtesy center fellow at the Stanford Woods Institute for the Environment. Co-authors include Krista Soderlund, Natalie Wolfenbarger, and Duncan Young of the University of Texas at Austin; Christopher Hamilton of the University of Arizona, Tucson; and Steven Vance of NASA’s Jet Propulsion Laboratory.
The research was supported by the G. Unger Vetlesen Foundation. Some of the work was done by the Jet Propulsion Laboratory, Caltech, under a contract with NASA.
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