NASA’s Cassini spacecraft will make a flyby of Saturn’s moon Enceladus Wednesday, passing through the moon’s plume of icy spray in a search for signs of life in its oceans.
Enceladus has plenty to offer scientists. It boasts an icy, barren landscape riddled with deep canyons, dubbed “tiger stripes.” Beneath its icy exterior is an ocean, heated in part by tidal forces from Saturn and another moon, Dione.
It also features seafloor vents that expel water at least 194 degrees Fahrenheit and plumes of water vapor and icy particles that are ejected from its surface in geyser-like spouts.
"Although the October 28th flyby won’t be the closest we’ve ever been to Enceladus, it is the closest flyby over the south pole and through the plume,” Linda Spilker, the Cassini Project Scientist at the Jet Propulsion Laboratory, said in a statement. “We’ll be exploring in situ a region of the plume that Cassini has never sampled before. This is very exciting for me!"
Early in its mission, Cassini found astounding geologic activity on Enceladus, including a towering plume of ice, water vapor and organic molecules spraying from its south polar region. Cassini later determined the moon has a global ocean and likely hydrothermal activity, meaning it could have the ingredients required to support simple life.
While the goal of this deep dive isn’t to detect life, the expectation is that it will provide fresh insights about how habitable the ocean environment is within Enceladus. There is the possibility that microscopic organisms similar to those that thrive around Earth's deep sea volcanic vents might exist there. To help answer the habitability question, scientists will be trying to determine how much hydrothermal activity is occurring within Enceladus.
Scientists also expect to learn more about the chemistry of the plume on Enceladus. The low altitude of the encounter should offer Cassini greater sensitivity to heavier, more massive molecules, including organics, than the spacecraft has observed in previous efforts.
The flyby should also help settle a debate of what the plume is made up of - column-like, individual jets, or sinuous, icy curtain eruptions -- or a combination of both. The answer would make clearer how material is getting to the surface from the ocean below.
Since 2004, Cassini has been orbiting Saturn at a distance of about 980 million miles from Earth. In that time, it has made dozens of flybys of Saturn’s moons.
In the future, a different spacecraft may journey across the solar system to visit icy Enceladus. This spacecraft, unlike Cassini, could be designed to land on Enceladus’ surface, near one of its “tiger stripes.” Such a lander would be able to take samples more directly, bypassing the plume altogether.
“Ideally, it could take samples from the edge of one of the tiger stripes,” Spilker said.