April 13, 2024

A single grain of ice may contain evidence of life on Europa and Enceladus

The Solar System’s icy ocean moons are prime targets in our search for life. Missions to Europa and Enceladus will explore these moons from orbit, improving our understanding of them and their potential to support life. Both worlds emit plumes of water from their inner oceans, and spacecraft sent to both worlds will examine these plumes and even sample them.

New research suggests that evidence of life in the lunar oceans may be present in just a single grain of ice, and our spacecraft could detect it.

It’s all due to improvements in scientific instruments, especially the mass spectrometer. Mass spectrometers can identify unknown chemical compounds by their molecular weights and also quantify known compounds. These instruments are now powerful enough to detect a small amount of cellular material.

“For the first time, we have shown that even a small fraction of cellular material can be identified by a mass spectrometer aboard a spacecraft,” said Fabian Klenner, postdoctoral researcher in Earth and space sciences at the University of Washington. . Klenner is also the lead author of a new paper in the journal Science Advances. “Our results give us more confidence that, using upcoming instruments, we will be able to detect Earth-like life forms, which we increasingly believe may be present on oceanic moons.”

The new research is “How to identify cellular material in a single grain of ice emitted by Enceladus or Europa”.

Mass spectrometers have been around for decades, but have improved rapidly in recent years. Researchers working on developing more powerful mass spectrometry have won two Nobel Prizes: one for Physics in 1989 and one for Chemistry in 2002. The 2002 prize is of particular interest in this research because it was awarded for the development of techniques that allowed mass spectrometers to be mass detect biological macromolecules, including proteins.

Now, spacecraft and rovers often have mass spectrometers in their instrument suite. NASA’s Curiosity rover has one, as does the Europa Clipper, which will be sent on its way to Europa in October 2024. It will arrive there in 2030, so this research makes its early arrival even more intriguing.

We know that Enceladus and Europa emit cryovolcanic plumes of material from their hidden oceans. The Cassini mission observed these eruptions coming from the south polar region of Enceladus. Eventually, the spacecraft came within 50 km of the icy moon and passed directly through the plumes. Using its mass spectrometer, it detected carbon dioxide, water, various hydrocarbons, and organic chemicals.

A false-color image of Enceladus’ erupting plumes. Image credit: NASA/ESA

“Enceladus has heat, water and organic chemicals, some of the essential building blocks needed for life,” said Dennis Matson in 2008, then a Cassini project scientist at NASA’s Jet Propulsion Laboratory.

Europa also has cryovolcanic plumes. The Hubble Space Telescope spotted them in 2012, and scientists working with data from the Galileo mission later said the data supported the discovery.

This composite image shows suspected water vapor plumes erupting at the 7 o'clock position off Jupiter's moon Europa.  The plumes, photographed by Hubble's Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter.  Hubble's ultraviolet sensitivity allowed the features, rising more than 100 miles above Europa's icy surface, to be discerned.  The Hubble data was obtained on January 26, 2014. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions.  Image credit: NASA/HST/STScI
This composite image shows suspected water vapor plumes erupting at the 7 o’clock position off Jupiter’s moon Europa. The plumes, photographed by Hubble’s Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter. Hubble’s ultraviolet sensitivity allowed the features, rising more than 100 miles above Europa’s icy surface, to be discerned. The Hubble data was obtained on January 26, 2014. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. Image credit: NASA/HST/STScI

When the Europa Clipper reaches its destination in 2030, it will use an instrument called SUDA, the SUrface Dust Analyzer. SUDA will use mass spectrometry to detect chemicals in Europa’s plumes. This research suggests that SUDA should be able to detect cellular material in a single grain of ice, if it is there.

This artist's illustration shows what Europe could be like.  Hot water containing organic material could flow from the ocean, through cracks in the ice, to space in ice grains via cryovolcanic plumes.  Image credit: NASA
This artist’s illustration shows what Europe could be like. Hot water containing organic material could flow from the ocean, through cracks in the ice, to space in ice grains via cryovolcanic plumes. Image credit: NASA

This research is based on a common bacteria found in Alaskan waters. Is called Sphingopyxis alaskensis, and the researchers chose it because it is very small. It also lives in cold environments and can survive with few nutrients. It’s possible that its small size and other attributes make it an analogue for any life that might exist in Europa’s ocean.

In their experiments, the researchers simulated how mass spectrometry could detect organic material in a tiny grain of ice. The results showed that, in addition to detecting expected non-organic chemicals, mass spectrometry also detected amino acids from Sphingopyxis alaskensis.

“They are extremely small, so they are, in theory, capable of fitting into ice grains emitted by an oceanic world like Enceladus or Europa,” Klenner said.

This research figure shows the cationic mass spectrum of cellular material equivalent to an S. alaskensis cell in a 15 μm diameter H2O droplet.  Although the mass spectrum is dominated by clusters of water, sodium water, potassium water, and ammonia water, amino acids, along with other metabolic intermediates from the S. alaskensis cell, can be identified.  The spectrum is an average of 224 individual spectra.  Image credit: Klenner et al.  2024.
This research figure shows the cationic mass spectrum of cellular material equivalent to an S. alaskensis cell in a 15 μm diameter H2O droplet. Although the mass spectrum is dominated by clusters of water, sodium water, potassium water, and ammonia water, amino acids, along with other metabolic intermediates from the S. alaskensis cell, can be identified. The spectrum is an average of 224 individual spectra. Image credit: Klenner et al. 2024.

The search for life on Europa may come down to individual grains of ice. This is partly because different molecules end up in different ice grains. If biological material is concentrated in ice grains, then it makes sense to detect them individually, rather than averaging the results from a larger ice sample.

But is there really biological material in the ice grains? How would it get there?

On Earth, bacterial cells are encased in protective lipid membranes. This means that they sometimes form a surface layer in the ocean or other bodies of water. If the same applies to any life that might exist on Europa or Enceladus, then these bacteria could form a skin on the ocean’s surface. On these icy moons, bubbles of gas that rise from the ocean and explode at the surface can incorporate cellular matter from bacteria into the plumes.

The drawing on the left shows Enceladus and its ice-covered ocean, with fissures near the south pole believed to penetrate through the icy crust.  The middle panel shows where life could thrive: on top of the water, in a proposed thin layer (shown in yellow), like in Earth's oceans.  The right panel shows that as gas bubbles rise and burst, bacterial cells can be launched into space with droplets that become the ice grains that were detected by Cassini.  A mass spectrometer must be able to detect cellular matter in a single grain of ice.  Image credit: European Space Agency
The drawing on the left shows Enceladus and its ice-covered ocean, with fissures near the south pole believed to penetrate through the icy crust. The middle panel shows where life could thrive: on top of the water, in a proposed thin layer (shown in yellow), like in Earth’s oceans. The right panel shows that as gas bubbles rise and burst, bacterial cells can be launched into space with droplets that become the ice grains that were detected by Cassini. A mass spectrometer must be able to detect cellular matter in a single grain of ice. Image credit: European Space Agency

“We describe here a plausible scenario for how bacterial cells could, in theory, be embedded in icy material formed from liquid water on Enceladus or Europa and then emitted into space,” Klenner said.

This is where mass spectrometry and SUDA come in. SUDA is much more powerful than previous mass spectrometers and has the ability to detect the fatty acids and lipids that can be released into plumes. While real DNA detection may seem like the Holy Grail, Klenner disagrees.

“For me, it’s even more exciting to look for lipids, or fatty acids, than it is to look for DNA building blocks, and the reason is because fatty acids seem to be more stable,” Klenner said.

In their paper, the researchers present their results clearly. “Our experiments show that even if just 1% of a cell’s constituents were contained in a 15-micrometer-diameter grain of ice (or a cell in a 70-micrometer-diameter grain), bacterial signatures would be apparent in the spectral data,” they explain.

This is good news for Europa Clipper and its SUDA instrument.

“With proper instrumentation, like the SUrface Dust Analyzer on NASA’s Europa Clipper space probe, it may be easier than we thought to find life, or traces of it, on icy moons,” said senior author Frank Postberg, professor of planetary sciences. at Freie Universität Berlin. “If life is present there, of course, and it wants to be encased in ice grains originating from an environment like an underground water reservoir.”

Leave a Reply

Your email address will not be published. Required fields are marked *