Ever since it was detected that the plumes of Saturn’s moon Enceladus contained organic matter, the possibility that there is a vast ocean beneath the icy body and that life exists there has been seriously considered. I am. However, because the ejection velocity of the plume is as high as approximately 400 m/s, it has been pointed out that biosignature molecules generated by life activities may be altered during detection.
A research team led by Sally E. Burke of the University of California, San Diego, conducted an experiment in which ice grains containing amino acids were accelerated and collided, replicating the plume of Enceladus. the result,Amino acids hardly change even at the fastest speed of 4.2km/s.It was revealed that. This research is likely to be fundamental research for detecting biosignature molecules in future exploration missions to icy objects.
[▲Figure 1: Water plume erupting from the south polar region of Enceladus (Credit: NASA, JPL-Caltech & Space Science Institute)]
■Does the material in the plume change in quality due to high-speed ejection?
There are predictions that some celestial bodies made primarily of ice are heated internally by tidal forces, causing the ice to melt and form vast oceans. For example, on Saturn’s moon Enceladus, plumes have been observed blowing out from the south pole into space, and it is almost certain that there is an ocean beneath the ice.
If there is an ocean that is geologically active due to heat generated by tidal forces and has been maintained for a long time, there is a possibility that a rich ecosystem exists, such as that around hydrothermal vents in the Earth’s deep sea. . Enceladus’ plume was analyzed by the Saturn probe Cassini, launched by NASA (National Aeronautics and Space Administration) and ESA (European Space Agency), and found that the ice contains components important for life, such as organic matter and salt. It turns out that. In particular, organic substances are attracting attention as important “biosignature molecules” because they may be produced in conjunction with life activities.
However, the ejection speed of the plume is approximately 400 m/s, and the ice containing organic matter collides with the spacecraft’s detector at high speed. The analyzer installed on the spacecraft uses the energy generated by high-speed collisions to vaporize and analyze molecules, but it is not well understood whether these collisions alter molecules. This is important because this alteration may accidentally create a biosignature molecule that does not actually exist, or may prevent a biosignature molecule that should be present from being detected.
■Amino acids have been found to be able to withstand high-speed collisions.
[▲Figure2:SchematicdiagramoftheexperimentalsetupIceparticlesthrownathighspeedcollidewithatargetandtheirmolecularstructureisanalyzedonthespot(Credit:SallyEBurkeetal)
Burke’s research team conducted an analysis using their own experimental equipment to examine the molecular alterations that occur in the plume. Burke et al.’s device is the only device in the world that can fly ice particles one hundredth of a meter or smaller at high speed and analyze the molecules contained in the ice. Burke and his colleagues bombarded metal with ice containing various concentrations of amino acids (histidine, arginine, and lysine) and investigated how the components changed. We also considered what would happen to the analytical values if sodium chloride, which is an important substance for sustaining life and has been detected in the plumes of Enceladus, was included.
the result,Amino acid molecules hardly change even when ice particles collide at speeds of up to 4.2 km/s.I understand that. On the other hand, it was observed that the presence of sodium chloride made it difficult to detect one amino acid, histidine. The results could help future probes analyze plumes to accurately quantify biosignature molecules.
On the other hand, in this analysis, it was not possible to calculate the critical speed at which amino acid molecules are completely denatured. Since the analytical sensitivity of amino acid molecules is high when collisions occur at speeds faster than about 3 km/s, it is important to explore the conditions related to the alteration of molecules. The research team plans to continue their research and explore molecular alterations in a wider range of environments.
Source
- Sally E. Burke, et al. “Detection of intact amino acids with a hypervelocity ice grain impact mass spectrometer”. (Proceedings of the National Academy of Sciences)
- Michelle Franklin. “Can Signs of Life be Detected from Saturn’s Frigid Moon?”. (University of California San Diego)
Written by Riri Aya
