Enceladus: Evidence for Liquid Water

by Paul Gilster on November 28, 2008

The phrase ‘liquid water’ is enough to quicken the pulse of the steeliest-eyed astrobiologist. We’ve long defined the concept of a habitable zone — that zone around a star in which life might flourish — by the presence of liquid water at the surface. But as we start pondering liquid water beneath the ices of outer satellites like Europa, we extend our investigations in exciting new ways. No wonder the new evidence of liquid water inside Enceladus received such attention in the mainstream media before the terrible news from Mumbai took center stage.

Image: In this artist’s concept, the Cassini spacecraft makes a close pass by Saturn’s inner moon Enceladus to study plumes from geysers that erupt from giant fissures in the moon’s southern polar region. Credit: Karl Kofoed (Drexel Hill, Pennsylvania).

On one level, liquid water on such cold, distant worlds is exciting because of the possibility of finding life that has arisen completely independent of what happened on Earth. At another, it’s energizing because it raises the prospect of other places where we might get further surprises. Joshua Colwell (University of Florida), who works on the Ultraviolet Imaging Spectrograph (UVIS) team supporting the Cassini mission, says it well:

“There are only three places in the solar system we know or suspect to have liquid water near the surface. Earth, Jupiter’s moon Europa and now Saturn’s Enceladus. Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary systems phenomenon, then it gets really interesting.”

Interesting indeed. Those remarkable geysers emanating from Enceladus’ south pole could involve water vapor escaping from a liquid underground source, becoming ice grains as they make their way through cracks in the crust. The recent work shows that the water vapor forms narrow jets as it emerges, a finding that seems to demand temperatures close to the melting point of ice to account for the observed behavior. The study was made during a stellar occultation as the plumes passed in front of the distant binary star Zeta Orionis, measuring the jets’ water vapor content and density (the secondary star was not a factor in the observations).

Four high-density water vapor jets were revealed against the background plume in this study, and it is their density and presumed temperature that support the liquid water model. All of which is enough to keep Enceladus squarely in Cassini’s sights as the spacecraft continues its extended mission, which lasts for two more years. The paper looks at competitive models, including the possibility that the jets are caused by the evaporation of volatile ices that are exposed to space when new vents open on Enceladus. It’s compelling that the timing of the jets in relation to the moon’s orbit around Saturn fails to coincide with this tidal model, but we have much to learn before declaring Enceladus a likely abode for life.

The paper is Hansen et al., “Water vapour jets inside the plume of gas leaving Enceladus,” Nature 456 (27 November 2008), pp. 477-479 (abstract).

{ 8 comments }

Paul Titze November 28, 2008 at 18:42

If anyone goes to Enceladus in the future might be worthwhile taking the fishing rod with you ;-)

Enzo November 28, 2008 at 21:57

Paul,

Believe it or not, people visiting Enceladus was supposed to happen in 1972.
I remember reading it in relation to Project Orion.

f you search for “Saturn” in the article below, you’ll find a faint reference to it :

Someone else might have a more precise reference to Enceladus and 1972.

As it happens, if we are lucky, we’ll get back to the moon in 2020 : yawn :-(.

In 1996, when serious indication of an ocean on Europa were found, an orbiter was supposed to be launched in 2003, arriving in 2008 – “only” 12 years later.
Nothing has happened and they are now talking about an Europa orbiter launched in 2020, arriving in 2030 :

That is 35 years after the first mission. If we follow the same snail pace, the next Enceladus/Titan mission will get there in 2043 (2008+35).
I’ll be old, but hopefully alive.

Enzo November 28, 2008 at 21:59
Darnell Clayton November 29, 2008 at 1:46

I think it would be better for us to seriously pursue placing a rover on the surface of Enceladus than on Europa–not to mention launch an ice melting probe to explore beneath the surface.

The reason I suggest this is because Enceladus is showing itself to be a lot more active than Europa (who seems to be warm thanks to daddy Jupiter) and may have a “warm” ocean beneath (or at least in the south pole).

Since its crust is probably thinner than Europa’s (a guess here–feel free to correct me if I am wrong here), it might make for a better science mission.

Administrator November 29, 2008 at 9:33

Enzo, here’s a link to a Centauri Dreams story on Enceladus and Project Orion:

http://www.centauri-dreams.org/?p=472

And you’re right, a mission to the moon was contemplated back in the days of Apollo. Extraordinary…

James M. Essig November 29, 2008 at 15:35

Hi Folks;

I seem to have accidently clicked on the Submit Comment button to soon.

However, note that number of large moons within our solar system. The total number of known moons is about 200. Each of the moons listed below has a diameter of 1,000 kilometers or greater.

Given the large diameter of these moons, the activity of tidal based fiction inducing interior heat, and/or natural radioactivity sustained heat within, the number of locations for which their might exist some form(s) of crude life is perhaps quite profound. At the very least, these moons might provide sub-terranian living space for future human settlements.

For Jupiter;

Callisto 4,800 Km;
Europa 3126 Km;
Ganymede 5276 Km;
Io 3,629 Km;

For Saturn;

Dione 1120 Km;
Iapetus 1436 Km;
Rhea 1528 Km;
Tethys 1060 Km;
Titan 5150 Km

For Uranus;

Ariel 1160 Km;
Oberon 1526 Km;
Titania 1,578 km;
Umbriel 1190 km;

For Neptune

Triton 2705 km;

Thanks;

Jim

ljk December 5, 2008 at 14:57

The motto, as quote here:

“Mars by 1965, Saturn by 1970.”

From this Web site:

http://www.islandone.org/Propulsion/ProjectOrion.html

And see this:

http://www.damninteresting.com/?p=679

ljk April 29, 2009 at 15:34

April 29, 2009

Salt in Enceladus’ Geysers Hints at Subsurface Liquid Ocean

Written by Nancy Atkinson

Planetary scientists say the geysers shooting from Saturn’s moon Enceladus are likely to come from a subsurface sea of liquid water. During the Cassini spacecraft’s fly-through of the geyser’s plume on October 9, 2008, the instruments on board were able to measure the molecular weight of the chemicals in the ice.

Detected were traces of sodium in the form of salt and sodium bicarbonate. The chemicals would have originated in the rocky core of Enceladus, so to reach a plume they must have leached from the core via liquid water.

Frank Postberg of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, and colleagues, are presenting their findings at the European Geophysical Union meeting in Vienna this week.

Full article here:

http://www.universetoday.com/2009/04/29/salt-in-enceladus-geysers-hint-at-subsurface-liquid-ocean/

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