Saturn’s icy moon may contain the building blocks of life

As technology and research in astrophysics continue to advance, one question remains: is there life elsewhere in the universe? The Milky Way alone has hundreds of billions of celestial bodies, but scientists often look for three crucial elements in their ongoing search: water, energy and organic matter. Evidence indicates that Saturn’s icy moon Enceladus is an “ocean world” that contains all three, making it a prime target in the search for life.

During its 20-year mission, NASA’s Cassini space probe discovered that plumes of ice were shooting from the surface of Enceladus at about 800 miles per hour (400 m/s). These plumes provide an excellent opportunity to collect samples and study the composition of Enceladus’ oceans and their potential habitability. However, until now it was unclear whether the speed of the plumes would fragment the organic compounds contained in the ice grains, thereby degrading the samples.

Now, researchers at the University of California, San Diego, have demonstrated unambiguous laboratory evidence that amino acids carried in these ice plumes can survive impact velocities of up to 2.6 miles (4.2 km). /s, which supports their detection during spacecraft sampling. Their conclusions appear in Proceedings of the National Academy of Sciences.

Starting in 2012, UC San Diego Distinguished Professor of Chemistry and Biochemistry Robert Continetti and colleagues custom built a unique aerosol impact spectrometer designed to study aerosol collision dynamics and of single particles at high speeds. Although it was not designed specifically to study the impacts of ice grains, it turned out to be exactly the ideal machine to do so.

“This device is the only one of its kind in the world that can select single particles and accelerate or decelerate them to chosen final velocities,” Continetti said. “From several microns in diameter to hundreds of nanometers, in a variety of materials, we are able to examine the behavior of particles, such as how they disperse or how their structures change upon impact.”

In 2024, NASA will launch the Europa Clipper, which will travel to Jupiter. Europa, one of Jupiter’s largest moons, is another ocean world and has an icy composition similar to Enceladus. It is hoped that Clipper or any future probe to Saturn will be able to identify a specific series of molecules in the ice grains that could indicate whether life exists in the subsurface oceans of these moons, but the molecules must survive their rapid ejection . of the moon and collected by the probe.

Although research has been done on the structure of some molecules found in ice particles, Continetti’s team is the first to measure what happens when a single grain of ice hits a surface.

To conduct the experiment, ice grains were created using electrospray ionization, where water is pushed through a needle held at high voltage, inducing a charge that breaks the water into droplets of smaller and smaller. The droplets were then injected under vacuum, where they freeze.

The team measured their mass and charge, then used imaging charge detectors to observe the grains as they flew through the spectrometer. A key part of the experiment was installing a microchannel plate ion detector to precisely time the moment of impact to the nanosecond.

The results showed that amino acids, often called the building blocks of life, can be detected with limited fragmentation up to impact speeds of 4.2 km/s.

“To get an idea of ​​what kind of life might be possible in the solar system, you want to know that there hasn’t been a lot of molecular fragmentation in the sampled ice grains, so you can get the fingerprint of all that makes it an autonomous life form,” Continetti said. “Our work shows that this is possible with Enceladus’ ice plumes.”

Continetti’s research also raises interesting questions for chemistry itself, including how salt affects the detectability of certain amino acids. Enceladus is thought to contain vast salty oceans, more numerous than there are on Earth. Since salt changes the properties of water as a solvent as well as the solubility of different molecules, this could mean that some molecules cluster on the surface of ice grains, making them more likely to be detected .

“The implications this has for detecting life elsewhere in the solar system without missions to the surface of these ocean moons are very exciting, but our work goes beyond biosignatures in ice grains,” Continetti said. “It also has implications for fundamental chemistry. We are excited by the prospect of following in the footsteps of Harold Urey and Stanley Miller, founding professors at UC San Diego, in studying the formation of the building blocks of life from chemical reactions activated by the impact of ice grains.”