Studies Point to Enceladus as a Promising Target in the Search for Life
Two new studies suggest Saturn's moon Enceladus may be well suited to hosting and revealing microbial life, as lab microbes survived simulated ocean conditions and plume ice appears to sort biosignatures into detectable grains.
Frank Postberg, a professor at Freie Universitat Berlin who was lead author of one of the studies and a co-author of the other, said the results were encouraging for the detection of life. "That is great news in the search for life," he said in a statement. "Future spacecraft will have to analyze many individual ice particles in the plume. But if they come across one with microbial material in it, they could identify biosignatures in the particle relatively easy with already available technology."
据 Space.com 报道，Enceladus is not the only place in the solar system with water, but its extensive liquid ocean and its seafloor make it a particular focus in the search for life. Scientists think hydrothermal processes, meaning the movement of or reactions with hot water beneath the surface, are taking place at the bottom of that ocean. Plumes shooting upward from the ocean also contain trace amounts of salts and organic compounds, which NASA's Cassini spacecraft found when it flew through the plumes more than a decade ago.
In Postberg's study, the team combined Cassini data, theoretical models and laboratory experiments to examine how water droplets in the plumes behave when they are ejected into space at speeds of up to 621 miles per hour (1,000 kilometers per hour). They found that the droplets do not freeze as quickly as expected. Earlier work assumed the freezing would happen instantaneously once the droplets reached space, but the researchers report that it actually occurs much more slowly. During freezing, the salts, organic compounds and possible signs of life in the droplets separate from one another, and as the particles are thrown into space they should frequently collide with icy cracks on the moon's surface. The result is tiny shards of frozen droplets whose components have been sorted apart, as though the moon had organized its oceanic ingredients into small frozen fragments.
According to Space.com, that sorting could make biosignatures easier for future spacecraft to identify, because a single ice particle may carry a concentrated sample rather than a diluted mixture.