How friendly is Enceladus' ocean to life?

February 5, 2016 by Elizabeth Howell , Astrobiology Magazine
Plumes erupting off the surface of Enceladus, an icy moon. Credit: NASA/JPL/SSI

How acidic is the ocean on Saturn's icy moon Enceladus? It's a fundamental question to understanding if this geyser-spouting moon could support life.

Enceladus is part of a family of icy worlds, including Europa (at Jupiter) and Titan (also at Saturn), populating our outer solar system. These bodies are some of the most promising places for life because they receive tidal energy from the gas giants they orbit and some contain liquid water.

The Cassini spacecraft has been taking regular measurements of Enceladus for more than a decade to evaluate its environment. One of the key factors influencing the habitability of an environment is its chemical composition, in particular its pH. On Earth, it's possible for life to exist near the extremes of the pH scale that ranges from 0 (battery acid) to 14 (drain cleaner). Knowing the pH can help us to identify geochemical reactions that affect the habitability of an environment, because many reactions cause predictable changes in pH.

Oceanography of another world

While we cannot stick a strip of pH paper into the ocean water on Enceladus to measure the pH directly, it can be estimated by looking at molecules in its plumes that change form in response to pH changes.

Serpentinization, which is believed to occur on Enceladus, may also happen on other moons such as Europa (pictured). Credit: NASA/JPL-Caltech/SETI Institute

Recently, geochemist Christopher Glein led a team that developed a new approach to estimating the pH of Enceladus' ocean using observational data of the carbonate geochemistry of plume material. This is a classic problem in geochemical studies of Earth (such as rainwater), but scientists can now solve the carbonate problem on an extraterrestrial body thanks to measurements of dissolved inorganic carbon by the Cosmic Dust Analyzer (CDA), and by the Ion and Neutral Mass Spectrometer (INMS) onboard Cassini.

Glein's team tried to create the most comprehensive chemical model to date of the ocean by accounting for compositional constraints from both INMS and CDA, such as the salinity of the plume. Their model suggests that Enceladus has a sodium, chloride and carbonate ocean with an alkaline pH of 11 or 12, close to the equivalent of ammonia or soapy water. The estimated pH is slightly higher by 1 to 2 units than an earlier estimate based on CDA data alone, but the different modeling approaches are consistent in terms of the overall chemistry of an alkaline ocean.

"It's encouraging that there is general agreement, considering that these approaches are based on spacecraft data from a plume. This is much more difficult than getting the pH of a swimming pool, so it would not be surprising if the models are missing some of the details. Of course, we are trying to reconcile the data as much as possible because the details may provide clues to understanding the eruptive processes that turn an ocean's chemistry into a plume," said Glein.

A paper based on Glein's research, "The pH of Enceladus' ocean," was published in Geochimica et Cosmochimica Acta in August. Glein is a research scientist at Southwest Research Institute, but completed the research while at the Carnegie Institution of Washington. The work was funded by the NASA Astrobiology Institute element of the Astrobiology Program at NASA.

Hydrothermal activity for life

A portion of the “Lost City” hydrothermal vents in the Atlantic Ocean, which may be most similar to what is happening on Enceladus. Credit: NASA

It is believed that Enceladus' alkaline chemistry comes from a geochemical process called serpentinization. This happens when a rock that is rich in magnesium and iron is converted to clay-type minerals. On Earth, we see this process in very limited locations, such as the low-temperature hydrothermal vent field named Lost City in the Atlantic Ocean.

"It's exactly what we would expect if there is a in contact with rocks on and below the ocean floor on Enceladus," Glein said.

In addition to a high pH, this process produces hydrogen gas, a potent fuel that can drive the formation of organic molecules that in some cases can be building blocks of life.

An unresolved question, however, is whether serpentinization is taking place now. If the activity is ongoing, this would provide habitable conditions, which could support an ecosystem similar to Lost City. If it occurred long ago, the high pH may be a relict and life may be less likely, although still not impossible if there are other sources of chemical energy.

Cassini did a final flyby of Enceladus in late October that targeted the chemistry of the plumes directly. The INMS team, which includes Glein, is searching for molecular hydrogen in that plume, which would be chemical evidence of active serpentinization. An absence of molecular hydrogen would be a sign that the serpentinization is extinct.

The data analysis from this flyby may be completed in time for the American Geophysical Union's fall meeting in December. Glein added that the planned NASA mission to Europa includes advanced descendants of both the CDA and INMS instruments, meaning that in a decade or two, scientists can start to make these same measurements at Europa. This will allow us to better understand the importance of serpentinization across the Solar System.

"On other icy worlds, if they have liquid water oceans, [serpentinization] should be inevitable because these bodies are massive mixtures of water and rock," he said. "Maybe the methane we see in Titan's atmosphere formed when hydrogen from serpentinization combined with deep carbon in a hydrothermal environment. There may also be on [dwarf planet] Pluto, through cryovolcanoes and a youthful surface. We expect there to be some degree of water-rock interaction on such worlds, setting the stage for serpentinization and the generation of hydrogen that could be utilized if there is anyone out there."

Explore further: Geochemical process on Saturn's moon linked to life's origin

More information: Christopher R. Glein et al. The pH of Enceladus' ocean, Geochimica et Cosmochimica Acta (2015). DOI: 10.1016/j.gca.2015.04.017

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17 comments

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cantdrive85
1.6 / 5 (14) Feb 05, 2016
Assuming of course there is actually an ocean...
Torbjorn_Larsson_OM
4.3 / 5 (12) Feb 05, 2016
Nice to have confirmation of the habitable range of alkaline pH. Speaking of confirmation, seeing H2 would also be confirmation of ongoing hydrothermal activity, since the silica grains Cassini observed can only come from active alkaline hydrothermal vents that sits more or less directly at the ocean floor under the jet openings.

"The composition and the limited size range (2 to 8 nanometres in radius) of stream particles indicate ongoing high-temperature (>90 °C) hydrothermal reactions associated with global-scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of Enceladus."

[ http://www.nature...262.html ]
Torbjorn_Larsson_OM
4.3 / 5 (12) Feb 05, 2016
@cantdrive: There are no assumptions in tested science, only decided constraints.

It has been known for years that there was an ocean under the jets rather than surface pockets. Famously Cassini could recently see after all these years of data collection that the ocean is global.

"Previous analysis of Cassini data suggested the presence of a lens-shaped body of water, or sea, underlying the moon's south polar region. However, gravity data collected during the spacecraft's several close passes over the south polar region lent support to the possibility the sea might be global. The new results -- derived using an independent line of evidence based on Cassini's images -- confirm this to be the case."

[ http://astrobiolo...dus.html ]
NiteSkyGerl
3.2 / 5 (18) Feb 05, 2016
He's pasted the same damned thing on every story he's commented on today. You really don't get it do you? There's no comment in his comment to debate. Get it? He came in here trolling for a story where he could say, "Dumb people that accomplish something in life, unlike me, I can tell you what you don't realize you're assuming". BEFORE he read the story.

For my money you either ignore those types, or hunt them down and teach them some manners. The rest is naive bullshit.
MalleusConspiratori
2 / 5 (4) Feb 05, 2016
I think you could put together a travel package based on that. Kind of like The Grand Tour crossed with an African safari vacation.
jljenkins
1 / 5 (2) Feb 05, 2016
Former contributer Pandora Hagadakis is way ahead of you. I think that's ryggesogn she's got there. http://cache.desk...nail.jpg
antigoresockpuppet
2.6 / 5 (5) Feb 05, 2016
The hard coded redirect to the home page when you log in from an article is kind of a clue that quality isn't exactly job #1.
Whydening Gyre
5 / 5 (8) Feb 06, 2016
For my money you either ignore those types, or hunt them down and teach them some manners. The rest is naive bullshit.

Dang, niteskygerl, you're feisty!
Torbjorn_Larsson_OM
4 / 5 (8) Feb 06, 2016
"You really don't get it do you? There's no comment in his comment to debate. ... For my money you either ignore those types, or hunt them down and teach them some manners. The rest is naive bullshit."

While not mentioning names, I think that is aimed at both behaviors, of troll and responders.

Yes, we do get it, it's part of a social dance. Anyone with 5 s attention span knows that cantdriveXX is a sorry excuse for a human being. And I am sometimes the first to tell people not to teach troll slime to roll onto the next thread.

But there is also the (minor, arguably) problem when a troll is first on a thread, and captures the science to some degree. An established (but again, arguable) response is to respond so any newbies can understand the science. It is, ironically, manners.

Go ahead, make my day, blow your top! I think that is as fun watching as trolling. (Yeah, I am perverse that way. Or maybe it is my swedish culture talking. =D)
Whydening Gyre
5 / 5 (6) Feb 06, 2016
Go ahead, make my day, blow your top! I think that is as fun watching as trolling. (Yeah, I am perverse that way. Or maybe it is my swedish culture talking. =D)

Careful, TL... You're letting your guard down...:-)
Zorcon
1.8 / 5 (5) Feb 06, 2016
He's pasted the same damned thing on every story he's commented on today. You really don't get it do you? There's no comment in his comment to debate. Get it? He came in here trolling for a story where he could say, "Dumb people that accomplish something in life, unlike me, I can tell you what you don't realize you're assuming". BEFORE he read the story.

For my money you either ignore those types, or hunt them down and teach them some manners. The rest is naive bullshit.


Cantdrive's definition of "conjecture" is different from ours. Once you realize that, his/her comments make perfect sense:

con·jec·ture

verb
1. to make a supposition without hard data from primitive religious texts to back it up.
"the infidel conjectured that 2+2=4"
Old_C_Code
5 / 5 (1) Feb 07, 2016
These bodies are some of the most promising places for life because they receive tidal energy from the gas giants they orbit


Enceladus' orbit is almost perfectly circular, no inclination and geocentric. Tidal forces?
jonesdave
3.7 / 5 (6) Feb 07, 2016
These bodies are some of the most promising places for life because they receive tidal energy from the gas giants they orbit


Enceladus' orbit is almost perfectly circular, no inclination and geocentric. Tidal forces?


"Enceladus is, like many satellites in the extensive systems of the giant planets, trapped in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior, and possibly driving the geological activity."

https://en.wikipe...nceladus
cantdrive85
1 / 5 (4) Feb 08, 2016
These bodies are some of the most promising places for life because they receive tidal energy from the gas giants they orbit


Enceladus' orbit is almost perfectly circular, no inclination and geocentric. Tidal forces?


"Enceladus is, like many satellites in the extensive systems of the giant planets, trapped in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior, and possibly driving the geological activity."

https://en.wikipe...nceladus

Oooh ooh, Wiki... Did you "edit" that yourself before you copied and pasted it?
jonesdave
3.4 / 5 (5) Feb 10, 2016
"Enceladus is, like many satellites in the extensive systems of the giant planets, trapped in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior, and possibly driving the geological activity."

https://en.wikipe...nceladus

Oooh ooh, Wiki... Did you "edit" that yourself before you copied and pasted it?


No, idiot. It's called evidence from observation. You could simply read a bunch of scientific papers on the subject if you'd rather (does the University for the Terminally Stupid have access to scientific journals?).
It was simply easier to direct the poster to the most accessible material.

Here's another wiki link: ht
jonesdave
3.4 / 5 (5) Feb 10, 2016
Whoops, link didn't work: http://rationalwi...universe
cantdrive85
1 / 5 (2) Feb 10, 2016
Ooh ooh, "rational" wiki. Even better....

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