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Cassini makes closest dive into Enceladus’ plumes

Artist's concept of Enceladus' plume

Artist’s concept of Enceladus’ icy plumes. NASA’s Cassini spacecraft completed its deepest-ever dive through it on Oct. 28, 2015. Image Credit: NASA/JPL-Caltech

In an effort to better understand hydrothermal activity inside Saturn’s moon Enceladus, which is believed to harbor a global subsurface ocean, NASA’s Cassini spacecraft conducted a daring plunge into the moon’s icy plumes on Wednesday, Oct. 28. The spacecraft flew within 30 miles (50 km) of the moon’s surface, taking pictures and collecting samples that the Cassini scientists hope will answer questions about Enceladus’ habitability for primitive life.

The Cassini spacecraft, which was launched in 1997 and has been orbiting Saturn since 2004, has flown closer to Enceladus’ surface in the past, but has never flown into the active plumes.

A view of Enceladus’ southern hemisphere in enhanced color (IR-green-UV).

A view of Enceladus’ southern hemisphere in enhanced color (IR-green-UV). The “tiger stripe” fractures, the source of plumes venting gas and dust into space, are prominently visible in the center. (Click to enlarge.) Image & Caption Credit: NASA/JPL-Caltech/SSI/Lunar and Planetary Institute, Paul Schenk

Hydrothermal activity on Enceladus involves chemical reactions between rock and hot water. The process has implications for the possible existence of primitive life.

The towering plumes are composed of ice particles, water vapor, and organic molecules emerging from fractures in Enceladus’ south polar region. This area is marked by regions described as “tiger stripes”, which are much warmer than the rest of the moon’s surface and likely the areas from which water is escaping from below.

Cassini discovered the huge plumes soon after arriving at Saturn. The spacecraft also found Enceladus to be geologically active and to host a global underground ocean where hydrothermal activity is likely taking place.

The ocean is located between 18 and 24 miles (30–40 km) beneath the moon’s icy surface. That surface is young and relatively free of impact craters because of regular resurfacing by “water volcanoes”. The moon’s large plumes are speculated by scientists to emanate from this subsurface ocean.

The presence of this ocean and likely hydrothermal activity occurring there raise the possibility that Enceladus could host microbial life.

While the purpose of Cassini’s fly through the plumes is not to determine whether such life is present, the data expected to be obtained from the flyby is likely to indicate the degree to which Enceladus’ ocean is habitable for simple life forms.

Most important is the question of whether Cassini detects molecular hydrogen in Enceladus’ plumes.

Previous flies through the plumes at higher altitudes were inconclusive. Scientists expect that the closer flyby will enable Cassini to have a higher degree of sensitivity, enabling it to detect more massive molecules, including organics. They also await to learn more about the amount of icy material the plumes are emitting into space, which could hold key information as to how long Enceladus has been an active world.

Currently, researchers do not know whether the plumes are composed of individual jets or are curtain-shaped. This knowledge, which they anticipate the flyby will provide, will better explain the process by which material in the plumes is traveling from the underground ocean to the moon’s surface.

Enceladus has an atmosphere that comprises largely of water vapor, presumed to come from gases escaping from the small world’s interior.

Photos from this flyby will be released on either Thursday, Oct. 29, or Friday, Oct. 30. Analysis of the particles found within the plumes is expected to take approximately one week.



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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Cassini continues to amaze us all!

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