Future spacecraft flying close to Enceladus may be able to detect amino acids, an essential class of organic compounds for life on Earth, in the explosive plumes erupting from the moon's surface, a new study suggests.

Enceladus, the sixth-largest moon orbiting Saturn, is of particular interest to astronomers hunting for extraterrestrial life in space. NASA's Cassini spacecraft spotted tantalizing signs that show it has a liquid ocean beneath its icy crust, and it may also contain the right chemical precursors necessary for amino acids to form. 

Amino acids are the building blocks of proteins, which perform vital functions in living organisms. The oxygen and nitrogen-based organic compounds detected in jets of material spewing from Enceladus' hydrothermal vents indicate that amino acids may be present in its oceans, but scientists haven't been able to confirm this yet.

Detecting them may be difficult since it would require a spacecraft sampling the material ejected from its surface. Would the amino acids survive collisions with apparatus measuring the chemical composition of the plumes? A team of researchers led by the University of California San Diego (UCSD) decided to study how fast a spacecraft could fly to maximize the chances of successfully detecting amino acids intact. 

"We knew from scientific descriptions of the spacecraft mission and sensors aboard that we needed to determine what happened to entrained molecules in the ice grain when single ice grains impacted an electrically conductive surface at speeds of several kilometers per second," Robert Continetti, co-author of a paper published in the journal of the Proceedings of the National Academy of Sciences and a professor of chemistry and biochemistry at UCSD, told The Register. 

Continetti and his colleagues built a spectrometer designed to study the chemical composition from the impact of droplets in aerosols. They can study particles of various sizes at different speeds and see how they splatter in collisions, and if certain compounds can still be measured by the spectrometer under specific conditions.

To simulate the plumes, the team created ice grains by running water through a needle under high voltage. The electrical charge breaks the water molecules apart into fragments, which are then injected into vacuum and freeze. The spectrometer can then analyze the masses and charges of these particles as they impacted at the detector.

"If extensive fragmentation occurs [during impact], it can be difficult to determine what the 'parent' mass of the unfragmented molecule is, and therefore identify it," Continetti explained. From the lab experiments, the team have calculated that a spacecraft can fly at speeds up to 4.2 kilometers per second through Enceladus' plume to detect amino acids with a spectrometer aboard if the compounds exist on the moon.

Astronomers have previously proposed a new flagship mission for NASA to spend $2.5 billion on a new spacecraft capable of orbiting and landing on Enceladus. The hypothetical Orbilander would fly through the moon's icy plumes, sweep the material, and analyze it with its instruments. The spacecraft would have to move at an appropriate speed to make sure the particles aren't destroyed upon impact. 

The latest research from UCSD shows their idea is possible. Detecting amino acids, however, would not confirm that there is alien life on Enceladus. "Life as we know it has a wide range of molecules involved, including fatty acids, lipid proteins, peptides, carbohydrates, and variations of these in the different components of cells or viruses," Continetti told us. 

"[Life] has a complex set of molecules, in varying distributions. But, knowing when fragmentation happens, opens the door to detecting life signatures in the material entrained in the ice grains that are ejected into space from Enceladus' subsurface ocean. You can think of our measurement as being one to determine if we're looking at eggs, or scrambled eggs," he said. ®

https://www.theregister.com//2023/12/06/heres_how_fast_a_spacecraft/