Despite being a rather small, Saturn’s 310-mile-wide (500 km) moon Enceladus also received star-treatment in this latest decadal report. That’s partly because the Cassini mission saw plumes of erupting liquid on Enceladus in 2005. And where there’s water, the chances for life go way, way up. The plumes also contained unusual amounts of possible biosignatures, such as methane, which can be a byproduct of biology.
The proposed “Orbilander” mission would arrive at Enceladus in the 2050s, orbit the moon for 18 months, then the entire craft would descend to the moon’s surface. By then, it will have flown through a few of those intriguing plumes, which are so active that their rejected material creates a thin ring around Saturn.
Once on the surface, the Orbilander would spend two years hunting for signs of biology. Enceladus’ surface is relatively safe for spacecraft, as it lacks the intense radiation baths of, for example, Jupiter’s moon Europa. According to NASA, “Enceladus has most of the chemical ingredients needed for life, and likely has hydrothermal vents spewing out hot, mineral-rich water into its ocean.”
Astrobiologists are particularly excited by the proposed Enceladus mission. University of Arizona Associate Professor of Ecology and Evolutionary Biology Regis Ferriere — who is a mathematician with an ecological bent — tells Astronomy that “Enceladus may be one of our best chances to find extant [still existing] life in our solar system.”
Ferriere was part of a team that published a 2021 paper in Nature Astronomy suggesting that the data Cassini produced shows “the observed plume composition is a likely outcome in model simulations that include the microbial activity, whereas it is an unlikely outcome in the simulations that only include the abiotic [non-biological] processes.”
In other words, the chemicals found in Enceladus’ plumes would make more sense if microbes were involved. And that’s where the new mission comes in.
“We won't know with just the Cassini data,” says Ferriere. “The Orbilander is a fantastic opportunity to gather new data that could solve the mystery. The Orbilander is designed to characterize organic molecules in the plume, and thus has the potential to detect the building blocks of Earth-like cells, such as amino acids or lipids.”
But even if the orbilander finds the chemistry of the Enceladus plumes is not produced by life, Ferriere says the data would be important: “We would still learn a great deal about the habitability of Enceladus and, more generally, of extraterrestrial environments that harbor liquid water.”
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