As astrophysics technology and research continue to advance, one question remains: Is life possible elsewhere in the universe? There are hundreds of billions of objects in the Milky Way alone, but scientists are constantly searching for three key elements: water, energy and organic matter. There is evidence that Saturn's icy moon Enceladus is an "ocean world" containing all three, making it a prime target for the search for life.
During its 20-year mission, NASA's Cassini spacecraft discovered plumes of ice erupting from the surface of Enceladus at speeds of about 800 miles per hour (400m/s). These plumes provide an excellent opportunity to collect samples and study the composition and potential habitability of Enceladus' ocean. However, so far it has been unclear whether the velocity of the plume would fragment any organic compounds contained in the ice particles, thereby degrading the sample.
Now, researchers from UC San Diego have shown clear laboratory evidence that amino acids transported in these ice plumes can survive impact velocities up to 4.2 km/s, supporting their detection during spacecraft sampling. Their findings were published in the Proceedings of the National Academy of Sciences (PNAS).
Beginning in 2012, Robert Continetti, distinguished professor of chemistry and biochemistry at UC San Diego, and his colleagues customized a unique aerosol impact spectrometer designed to study the high-speed collision dynamics of single aerosols and particles. While it wasn't specifically built to study the effects of ice particles, it turned out to be just the right machine to do so.
"This device is the only one of its kind in the world that can select individual particles and accelerate or decelerate them to a selected final velocity," Continetti said. "In a variety of materials, from a few microns in diameter to hundreds of nanometers, we are able to examine particle behavior, such as how they disperse or how their structure changes upon impact."
In 2024, NASA will launch the Europa Clipper to Jupiter. Europa, one of Jupiter's largest moons, is another ocean world with an icy composition similar to Enceladus. NASA hopes Clipper or any future Saturn probe will be able to identify a specific set of molecules in the ice grains that could indicate whether life exists in these moons' subsurface oceans, but those molecules would need to survive their rapid ejections.
Although the structure of certain molecules in ice particles has been studied, Continetti's team is the first to measure what happens when individual ice particles hit a surface.
For the experiments, ice particles were created using electrospray ionization, in which water is pushed through a needle held under high pressure, inducing an electrical charge that breaks the water into smaller and smaller droplets. The droplets are then injected into a vacuum and frozen there. The team measured their mass and charge, then used an image charge detector to watch the particles as they flew through a spectrometer. A key element of the experiment was the installation of a microchannel plate ion detector to precisely time the moment of impact to nanoseconds.
The results show that amino acids, often called the building blocks of life, can be detected with limited fragmentation at impact speeds of 4.2 kilometers per second.
"In order to understand what kind of life might exist in the solar system, you want to know that there aren't a lot of molecular fragments in the sample of ice particles, so that you can get a fingerprint that any life formed. It was an independent life form," Continetti said. "Our work shows that this is possible with Enceladus' ice plumes."
This study also raises interesting questions about chemistry itself, including how salt affects the detectability of certain amino acids. Enceladus is believed to have a vast salty sea - more salty than there are on Earth. Since salt changes the properties of water as a solvent and the solubility of different molecules, this could mean that certain molecules clump on the surface of the ice particles, making them more likely to be detected.
"The implications for detecting life elsewhere in the solar system without traveling to the surface of these ocean world moons are very exciting," Continetti said, "but our work goes beyond just biosignatures in ice particles. It also has implications for basic chemistry. We are excited to follow in the footsteps of UC San Diego founding professors Harold Urey and Stanley Miller in studying how chemical reactions activated by ice particle impacts form the building blocks of life."
Compiled source: ScitechDaily