NASA's Saturn-orbiting Cassini spacecraft is on track for a deep but quick plunge through plumes of water vapor shooting out hundreds of miles into space from the planet's small, ocean-bearing moon Enceladus.
Cassini, which has been surveying the Saturn system for 11 years, will fly as close as 30 miles above the moon's southern polar region, about 20 miles closer than any previous pass through the plumes.
PHOTO: Cassini Watches Enceladus Fizz into Space
Scientists believe the plumes stem from a global liquid ocean that is sealed beneath Enceladus' icy face. They suspect tidal heating is responsible for the ocean, a process which also may mean the interior of Enceladus is suitable for life.
Cassini does not have life-detection instruments, but the flyby, which will take place at around 1 p.m. EDT on Wednesday, is expected to provide key details that will help scientists assess whether Enceladus is a suitable habitat for life.
For example, scientists want to confirm if molecular hydrogen is present in the plumes, a finding that would support other evidence of hydrothermal activity on the sea floor.
"The amount of hydrogen emission will reveal how much hydrothermal activity is actually occurring ... with implications for the amount of energy that's available -- energy (being) a key ingredient for habitability," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
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Scientists also want to better understand the chemistry of the material in the plumes, which in addition to water vapor and ice contain organics and a variety of gases, including methane and carbon dioxide. Collecting and analyzing samples from closer to the base of the plumes should yield larger particles and higher concentrations of gas.
"We might find new organics that we haven't seen previously, or are just at the limits of our detection," Spilker said.
A third goal of the flyby is to provide details on the structure of the plumes, such as whether they jet, formation-style, from cracks in the ice, or if they spray like a curtain along the whole length of the fractures. That information will help scientists determine how long Enceladus has been venting water into space.
The 19,000 mph-flyby will be over in a fraction of a second, but scientists say the drop of water Cassini will collect is enough to spill some of Enceladus' secrets.
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"This is a very big step in a new era of exploring ocean worlds in our solar system ... bodies with great potential to provide oases for life," said Cassini program scientist Curt Niebur.
Cassini, which is due to end its mission in 2017, is slated to make a final pass through Enceladus' plumes in December.
In related research, scientists on Tuesday released the results of laboratory tests with gases that are similar in composition to those observed in Encleadus' plumes. Writing in this week's Nature Communications, the researchers were able to create liquids at conditions found on Enceladus. The results suggest that the same minerals formed on Enceladus have been found in primitive meteorites, and that Enceladus may have formed very early in the solar system's history.
The lab tests show Enceladus also could be producing hydrogen, "which could provide energy for possible life forms beneath the surface," a summary of the research said.