Researchers model the source of the eruption on the moon of Jupiter Europe

On Jupiter’s icy Europa moon, powerful eruptions can spit out into space, raising questions among hopeful astrobiologists on Earth: What would explode in plumes several miles high? Could they contain signs of extraterrestrial life? And where would they come from in Europe? A new explanation now points to a source closer to the frozen surface than expected.

Rather than originate from the depths of Europe’s oceans, some eruptions may originate from pockets of water embedded in the icy shell itself, new evidence from researchers at Stanford University, University of the Arizona, University of Texas, and NASA’s Jet Propulsion Laboratory.

Using images collected by NASA’s Galileo spacecraft, researchers developed a model to explain how a combination of freezing and pressurization could lead to a cryovolcanic eruption or water explosion. The results, published on November 10 in Geophysical research letters, have implications for the habitability of Europe’s underlying ocean – and may explain eruptions on other frozen bodies in the solar system.

Messengers of life?

Scientists have speculated that the vast ocean hidden beneath Europe’s icy crust may contain elements necessary for life. But unless you send a submersible to the Moon to explore, it’s hard to know for sure. This is one of the reasons why Europa’s plumes have generated so much interest: If the eruptions originate from the underground ocean, the elements could be more easily detected by a spacecraft like the one planned for the next mission. NASA’s Europa Clipper.

But if the plumes originate from the icy shell of the moon, they may be less welcoming to life, as it is more difficult to sustain 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 come from is very important to whether future explorers of Europe might have a chance to actually detect life from space without probing the ocean of Europe,” said the lead author Gregor Steinbrügge, postdoctoral researcher at Stanford’s School of Earth, Energy. And environmental sciences (Stanford Earth).

Researchers focused their analyzes on Manannán, an 18-mile-wide crater in Europe that was created by impact with another celestial object tens of millions of years ago. Believing 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 in the icy shell could have caused the water to erupt.

“The comet or asteroid hitting the ice shell was basically a great experiment that we use to build hypotheses to test,” said co-author Don Blankenship, senior researcher at the Institute of Geophysics at the University of Canada. Texas (UTIG) and Principal Investigator. of the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instrument which will fly on Europa Clipper. “The UTIG Polar and Planetary Sciences team is currently evaluating the ability of this instrument to test these hypotheses.”

The model indicates that as Europe’s water turned to ice during the later stages of impact, pockets of water with increased salinity could be created on the moon’s surface. In addition, these pockets of salt water can migrate laterally through the ice shell of Europe, melting adjacent regions of less brackish ice, and therefore become even saltier in the process.

“We have developed a way for a pocket of water to move sideways – and this is very important,” said Steinbrügge. “It can move along thermal gradients, from cold to hot, and not just downwards, because it is pulled by gravity.

A salty driver

The model predicts that when a pocket 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 plume left a distinctive mark: a spider-like feature on the surface of Europe that was observed by Galileo imagery and incorporated into the researchers’ model.

“Even though the plumes generated by the migration of brine pockets would not provide a direct glimpse of the European ocean, our results suggest that the European ice shell itself is very dynamic,” said Joana Voigt , co-lead author, graduate research assistant at the University of Arizona, Tucson.

The relatively small size of the plume that would form at Manannán indicates that the impact craters probably cannot explain the source of other larger plumes over Europe that have been assumed based on data from Hubble and Galileo, the researchers say . But the process modeled for the Manannán eruption could occur on other frozen bodies, even without an impact event.

“The migration of brine pockets is not only applicable to Europan craters,” Voigt said. “Instead, the mechanism could provide explanations for other icy bodies where thermal gradients exist.”

The study also provides estimates of the salt level of Europe’s frozen surface and ocean, which in turn could affect the transparency of its ice shell to radar waves. Calculations, based on Galileo imagery from 1995 to 1997, show that Europe’s ocean may be about a fifth as salty as Earth’s ocean – a factor that will improve the capability of the mission’s radar sounder. Europa Clipper to collect data from its interior.

The results may be daunting for astrobiologists, hoping that Europe’s erupting plumes may contain clues to the internal ocean’s ability to support life, given the implication that the plumes do not have to connect. to the European ocean. However, the new model offers information on how to unravel Europe’s complex surface features, which are subject to hydrological processes, the pull of Jupiter’s gravity, and tectonic forces hidden in the icy moon.

“It makes the shallow subsoil – the ice shell itself – a much more exciting place to think about,” said co-author Dustin Schroeder, assistant professor of geophysics at Stanford. “It opens up a whole new way of thinking about what happens with water near the surface.”