Enceladus Plumes Are Geysering Less: Saturn's Possibly Habitable Moon Mystery

Summary: A 2015 flyby alert that Enceladus plumes are geysering 30 to 50 percent less is explored Dec. 14 at the annual American Geophysical Union fall meeting.

artist's concept of Cassini spacecraft diving into Enceladus plumes during Oct. 28, 2015's super-close flyby: NASA/JPL-CalTech, Public Domain, via NASA Jet Propulsion Laboratory

A Saturn moon mystery is playing out with Enceladus plumes geysering 30 to 50 percent less from highly saline subsurface reservoirs, according to findings from 2015 flybys presented Monday, Dec. 14, 2015, at the American Geophysical Union’s annual fall meeting in San Francisco.

Possible explanations for reduced geysering by Enceladus plumes include buildup on the walls of the plumes’ vents or variability in the water pressure of the plumes’ source reservoirs.

“But why they would all act together is totally beyond me,” says Andrew Ingersoll, American Geophysical Union presenter and Caltech professor of planetary science.

Dr. Ingersoll and Miki Nakajima, postdoctoral fellow at the Carnegie Institution for Science, point out during Monday’s AGU sessions that ice particles in Enceladus’s icy, vaporous plumes yield high salinity of around 1 percent. The highly saline icy particles escape from a subsurface liquid ocean that serves as the source of Enceladus plumes.

Enceladus plumes emerge from cracks, known as tiger stripes, at the moon’s south polar region. Acting as vents, tiger stripes measure lengths of approximately 80 miles (130 kilometers). About 25 miles (40 kilometers) separate each tiger stripe in the group’s almost parallel formation, known individually as sulcus (a Latin agricultural term for furrow) and in the plural as sulci.

Findings presented at the American Geophysical Union (AGU) meeting represent ongoing exploration of the sixth-largest of Saturn’s 62 known moons. With a diameter of 313 miles (504 kilometers), Enceladus attracts much hope and interest from the National Aeronautics and Space Administration (NASA) as a possible site for human habitability. Although not designed to detect evidence of life, Cassini plunged into Enceladus plumes during flybys on Oct. 14 and 28, 2015. Initial analyses from Cassini’s dives indicate the possibility of hospitable conditions for at least microscopic life forms below Enceladus’s surface.

“This really is a world with a habitable environment in its interior,” states Jonathan Lunine, AGU presenter and David C. Duncan Professor in the Physical Sciences at Cornell University.

The last close flyby occurred Saturday, Dec. 19, 2015, at 12:49 p.m. Eastern Standard Time (5:49 p.m. Coordinated Universal Time). The final flyby’s focus on the amount of heat emanating from Enceladus’s interior will reveal important insights into the moon's geological activities.

Observation of Enceladus by Cassini continues after the final flyby, but at greater distances. The unmanned spacecraft has been gathering information on the Saturn system since entering orbit around the sixth planet from the sun on July 1, 2004.

Cassini first imaged Enceladus plumes in January and February 2005. Ice volcanoes, known as cryovolcanoes, form on icy moons of giant host planets (Jupiter, Saturn, Uranus, Neptune) with orbits beyond the Solar System's frost line.

Consistent with the naming practice for Enceladean sulci, tiger stripes honor namesakes in The One Thousand and One Nights, a multi-century compilation of Middle Eastern and South Asian tales. The four main tiger stripes that vent Enceladus’s ocean are known officially as Alexandria Sulcus, Baghdad Sulcus, Cairo Sulcus, and Damascus Sulcus. Camphor Sulcus, a smaller feature, branches from Alexandria Sulcus.

Gravity data, yielded by analyzing more than seven years of Cassini spacecraft’s images, attribute Enceladus’s tiny wobble to a global subsurface ocean. A paper published online Sept. 11, 2015, in Icarus confirms the long-suspected oceanic presence.

“We’ve been following a trail of clues on Enceladus for 10 years now,” says Bonnie Buratti, a Cassini science team member and icy moons expert at NASA’s Jet Propulsion Laboratory, as she describes NASA’s commitment, via three final close flybys in October and December 2015, to the decipherment of Enceladus’s intriguing clues. She explains: “The amount of activity on and beneath this moon’s surface has been a huge surprise to us. We’re still trying to figure out what its history has been, and how it came to be this way.”

American planetary scientist and physicist Jonathan Lunine's AGU 2015 presentation considers Enceladus Life Finder's (ELF) sensitive life-searching instrumentation: James Tuttle Keane @jtuttlekeane via Twitter Dec. 14, 2015

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Enceladus plumes: NASA/JPL-CalTech, Public Domain, via NASA Jet Propulsion Laboratory @ http://www.jpl.nasa.gov/news/news.php?release=2015-373

"The spacecraft is healthy after the #Enceladus flyby. Pictures likely in next day or two.": CassiniSaturn‏ @CassiniSaturn via Twitter Oct. 28, 2015, @ https://twitter.com/CassiniSaturn/status/659522010167427072

American planetary scientist and physicist Jonathan Lunine's AGU 2015 presentation considers Enceladus Life Finder's (ELF) sensitive life-searching instrumentation: James Tuttle Keane‏ @jtuttlekeane via Twitter Dec. 14, 2015, @ https://twitter.com/jtuttlekeane/status/676462925335289856

For further information:

Anderson, Paul Scott. "Cassini Prepares for Last Epic Flyby of Saturn's Ocean Moon Enceladus." America Space.
Available @ http://www.americaspace.com/?p=89744

Carnegie Institution of Washington Department of Terrestrial Magnetism. "Monday, 14 December 2015 @AGU." Carnegie Science DTM > News.
Available @ http://dtm.carnegiescience.edu/news/monday-14-december-2015-agu

CassiniSaturn‏ @CassiniSaturn. "The spacecraft is healthy after the #Enceladus flyby. Pictures likely in next day or two." Twitter. Oct. 28, 2015.
Available @ https://twitter.com/CassiniSaturn/status/659522010167427072

James Tuttle Keane‏ @jtuttlekeane. "We need to go back to Enceladus w/ better mass spectrometers - for finding life (Jonathan Lunine P11D-09) #AGU15." Twitter. Dec. 14, 2015.
Available @ https://twitter.com/jtuttlekeane/status/676462925335289856

Klotz, Irene. "Life-Friendly Chemistry Revealed Inside Saturn Moon." Seeker > Space. Dec. 15, 2015.
Available @ http://www.seeker.com/life-friendly-chemistry-revealed-inside-saturn-moon-1770615079.html#news.discovery.com

NASA Jet Propulsion Laboratory. "Deep Dive into Enceladus Plume." YouTube. Oct. 26, 2015.
Available @ http://www.youtube.com/watch?v=BZ1KowQXc3Y

Wall, Mike. "The Geysers on Saturn's Moon Enceladus Are Mysteriously Losing Steam." Space.com > Science & Astronomy. Dec. 16, 2015.
Available @ http://www.space.com/31385-saturn-moon-enceladus-geysers-losing-steam.html