An artist’s rendition of Saturn’s moon Enceladus depicts hydrothermal activity on the seafloor and cracks in the moon’s icy crust that allow material from the watery interior to be ejected into space. New research shows that instruments destined for the next missions could find traces of a single cell in a single ice grain contained in a plume. Credit: NASA/JPL-Caltech
Research on ice grains from moons like Enceladus and Europa shows potential for detecting signs of life, paving the way for upcoming space missions with advanced detection instruments.
The ice-encrusted oceans of some of the moons orbiting
This image shows red streaks across the surface of Europa, the smallest of Jupiter’s four large moons. The upcoming Europa Clipper mission will send instruments to investigate this moon. New research shows that one of these instruments destined for the next mission could find traces of a single cell in a single ice grain ejected from the planetary body’s interior. Credit: NASA/JPL/Galileo
The open-access study was published on March 22 in SUrface Dust Analyzer onboard Europa Clipper, can detect cellular material in one out of hundreds of thousands of ice grains.
![Enceladus Subsurface Ocean Cracks Near South Pole](https://scitechdaily.com/images/Enceladus-Subsurface-Ocean-Cracks-Near-South-Pole-777x398.jpg)
The drawing on the left depicts Enceladus and its ice-covered ocean, with cracks near the south pole that are believed to penetrate through the icy crust. The middle panel shows where authors believe life could thrive: at the top of the water, in a proposed thin layer (shown yellow) like on Earth’s oceans. The right panel shows that as gas bubbles rise and pop, bacterial cells could get lofted into space with droplets that then become the ice grains that were detected by Cassini. Credit: European Space Agency
Potential for Discovering Life
The study focused on Sphingopyxis alaskensis, a common bacterium in waters off Alaska. While many studies use the bacterium Escherichia coli as a model organism, this single-celled organism is much smaller, lives in cold environments, and can survive with few nutrients. All these things make it a better candidate for potential life on the icy moons of Saturn or Jupiter.
“They are extremely small, so they are in theory capable of fitting into ice grains that are emitted from an ocean world like Enceladus or Europa,” Klenner said.
Results show that the instruments can detect this bacterium, or portions of it, in a single ice grain. Different molecules end up in different ice grains. The new research shows that analyzing single ice grains, where biomaterial may be concentrated, is more successful than averaging across a larger sample containing billions of individual grains.
![Enceladus Bubbles](https://scitechdaily.com/images/Enceladus-Bubbles-777x536.jpg)
The left panel shows the kilometers-thick icy crust believed to encapsulate Saturn’s moon Enceladus. Filling the crack is salty water with a proposed thin layer (shown orange) at its surface. The right panel shows that as gas bubbles rise and pop, they combine with organic material and get lofted into the spray. Credit: Postberg et al. (2018)/Nature
A recent study led by the same researchers showed evidence of phosphate on Enceladus. This planetary body now appears to contain energy, water, phosphate, other salts and carbon-based organic material, making it increasingly likely to support lifeforms similar to those found on Earth.
The authors hypothesize that if bacterial cells are encased in a lipid membrane, like those on Earth, then they would also form a skin on the ocean’s surface. On Earth, ocean scum is a key part of sea spray that contributes to the smell of the ocean. On an icy moon where the ocean is connected to the surface (e.g., through cracks in the ice shell), the vacuum of outer space would cause this subsurface ocean to boil. Gas bubbles rise through the ocean and burst at the surface, where cellular material gets incorporated into ice grains within the plume.
“We here describe a plausible scenario for how bacterial cells can, in theory, be incorporated into icy material that is formed from liquid water on Enceladus or Europa and then gets emitted into space,” Klenner said.
The SUrface Dust Analyzer onboard Europa Clipper will be higher-powered than instruments on past missions. This and future instruments also will for the first time be able to detect ions with negative charges, making them better suited to detecting fatty acids and lipids.
“For me, it is even more exciting to look for lipids, or for fatty acids, than to look for building blocks of DOI: 10.1126/sciadv.adl0849
The study was funded by the European Research Council, NASA and the German Research Foundation (DFG). Other co-authors are Janine Bönigk, Maryse Napoleoni, Jon Hillier and Nozair Khawaja at the Freie Universität Berlin; Karen Olsson-Francis at The Open University in the U.K.; Morgan Cable and Michael Malaska at the NASA Jet Propulsion Laboratory; Sascha Kempf at the University of Colorado, Boulder; and Bernd Abel at the University of Leipzig.