Strongest evidence yet indicates Enceladus hiding saltwater ocean

Jun 22, 2011
This image shows icy spray spewing from Saturn's moon, Enceladus. Credit: NASA/JPL/Space Science Institute

(PhysOrg.com) -- Samples of icy spray shooting from Saturn's moon Enceladus collected during Cassini spacecraft flybys show the strongest evidence yet for the existence of a large-scale, subterranean saltwater ocean, says a new international study led by the University of Heidelberg and involving the University of Colorado Boulder.

The new discovery was made during the Cassini-Huygens mission to , a collaboration of NASA, the and the Italian Space Agency. Launched in 1997, the mission spacecraft arrived at the Saturn system in 2004 and has been touring the giant ringed planet and its vast moon system ever since.

The plumes shooting water vapor and tiny grains of ice into space were originally discovered emanating from Enceladus -- one of 19 known moons of Saturn -- by the Cassini spacecraft in 2005. The plumes were originating from the so-called "tiger stripe" surface fractures at the moon's south pole and apparently have created the material for the faint E Ring that traces the orbit of Enceladus around Saturn.

During three of Cassini's passes through the plume in 2008 and 2009, the Analyser, or CDA, on board measured the composition of freshly ejected plume grains. The icy particles hit the detector's target at speeds of up to 11 miles per second, instantly vaporizing them. The CDA separated the constituents of the resulting vapor clouds, allowing scientists to analyze them.

The study shows the ice grains found further out from Enceladus are relatively small and mostly ice-poor, closely matching the composition of the E Ring. Closer to the moon, however, the Cassini observations indicate that relatively large, salt-rich grains dominate.

Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. The tiger stripes are fissures that spray icy particles, water vapor and organic compounds. Image credit: NASA/JPL/Space Science Institute

"There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than the salt water under Enceladus' icy surface," said Frank Postberg of the University of Germany, lead author of a study being published in Nature on June 23. Other co-authors include Jürgen Schmidt from the University of Potsdam, Jonathan Hillier from Open University headquartered in Milton Keynes, England, and Ralf Srama from the University of Stuttgart.

"The study indicates that 'salt-poor' particles are being ejected from the underground ocean through cracks in the moon at a much higher speed than the larger, salt-rich particles," said CU-Boulder faculty member and study co-author Sascha Kempf of the Laboratory for Atmospheric and Space Physics.

"The E Ring is made up predominately of such salt-poor grains, although we discovered that 99 percent of the mass of the particles ejected by the plumes was made up of salt-rich grains, which was an unexpected finding," said Kempf. "Since the salt-rich particles were ejected at a lower speed than the salt-poor particles, they fell back onto the moon's icy surface rather than making it to the E Ring."

According to the researchers, the salt-rich particles have an "ocean-like" composition that indicates most, if not all, of the expelled ice comes from the evaporation of liquid salt water rather than from the icy surface of the moon. When salt water freezes slowly the salt is "squeezed out," leaving pure water ice behind. If the plumes were coming from the surface ice, there should be very little salt in them, which was not the case, according to the research team.

The researchers believe that perhaps 50 miles beneath the surface crust of Enceladus a layer of water exists between the rocky core and the icy mantle that is kept in a liquid state by gravitationally driven tidal forces created by Saturn and several neighboring moons, as well as by heat generated by radioactive decay.

According to the scientists, roughly 440 pounds of water vapor is lost every second from the plumes, along with smaller amounts of ice grains. Calculations show the liquid ocean must have a sizable evaporating surface or it would easily freeze over, halting the formation of the plumes. "This study implies that nearly all of the matter in the Enceladus plumes originates from a saltwater ocean that has a very large evaporating surface," said Kempf.

Salt in the rock dissolves into the water, which accumulates in a liquid ocean beneath the icy crust, according to the Nature authors. When the outermost layer of the Enceladus crust cracks open, the reservoir is exposed to space. The drop in pressure causes the liquid to evaporate into a vapor, with some of it "flash-freezing" into salty ice grains, which subsequently creates the plumes, the science team believes.

" is a tiny, icy moon located in a region of the outer Solar System where no liquid water was expected to exist because of its large distance from the sun," said Nicolas Altobelli, ESA's project scientist for the . "This finding is therefore a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life may be sustainable on icy bodies orbiting gas giant planets."

The Huygens probe was released from the main spacecraft and parachuted through the atmosphere to the surface of Saturn's largest moon, Titan, in 2005.

The is carrying 12 science instruments, including a $12.5 million CU-Boulder ultraviolet imaging spectrograph designed and built by a LASP team led by Professor Larry Esposito.

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User comments : 29

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grgfraiser
4.6 / 5 (7) Jun 22, 2011
thats were we need to look for life
HannesAlfven
1.3 / 5 (16) Jun 22, 2011
Re: ""There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than the salt water under Enceladus' icy surface," said Frank Postberg of the University of Germany, lead author of a study being published in Nature on June 23"

It's questionable that the researchers actually investigated alternative frameworks. Yes, within their preferred gravitational framework for the universe -- the conventional theory which they were taught in college -- researchers are limited in what they can infer. But, did they actually go to the effort to learn the alternative plasma-based framework which encompasses the electrical machining inference? The answer to this question is traditionally an uncurious dismissal.

This becomes a glaring problem when we are talking about sending a probe out. You have to investigate the alternative framework before you spend many millions of dollars on this.
Scientist_Steve
5 / 5 (3) Jun 22, 2011
@grgfraiser
Agreed. Now if we could only figure out how to equip a lander that is capable drilling through 50 miles of ice, it would be a possibility.
Yellowdart
1 / 5 (3) Jun 22, 2011
"Enceladus is a tiny, icy moon located in a region of the outer Solar System where no liquid water was expected to exist because of its large distance from the sun," said Nicolas Altobelli, ESA's project scientist for the Cassini-Huygens mission. "This finding is therefore a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life may be sustainable on icy bodies orbiting gas giant planets."


What? Can you logically jump to that suggestion before dealing with where the salt water came from??

Your looking at the remarkable power of tidal pumping, and yet you can't even look under your own noses.
that_guy
4.8 / 5 (8) Jun 22, 2011
"roughly 440 pounds of water vapor is lost every second."

Pounds are a measure of weight in a given gravitational environment, so is that 440 pounds as measured from earth, or 440 pounds as measured from Enceladus?

Technically, they should be using a unit of Mass (Such as a Kilogram) in order to clear up any confusion.

Just stirring the pot :)

NickFun
1.2 / 5 (5) Jun 22, 2011
A moon that small must have a way of replenishing its water supply. Surely it can't be spewing water for hundreds of millions of years and still have any left. Could there be something else lurking beneath the surface?
tkjtkj
4 / 5 (1) Jun 22, 2011
@grgfraiser
Agreed. Now if we could only figure out how to equip a lander that is capable drilling through 50 miles of ice, it would be a possibility.

That is not all that difficult to do .. The heat of radioactive decay of a capsule would do it .. but rather, the problem would then be getting the data collected back to the surface, for earth transmission. If that cant be solved, then no 'drilling' would be appropriate.
Perhaps a reel containing 100 km of wire might do, if no seismic ice shifting occurs as the capsule melts its way down, as behind it the water refreezes ..
sstritt
4.2 / 5 (5) Jun 22, 2011
A moon that small must have a way of replenishing its water supply. Surely it can't be spewing water for hundreds of millions of years and still have any left. Could there be something else lurking beneath the surface?
Not that hard to believe- just do the math. Besides, who knows how big it was in the past.
fmfbrestel
5 / 5 (5) Jun 22, 2011
A moon that small must have a way of replenishing its water supply. Surely it can't be spewing water for hundreds of millions of years and still have any left. Could there be something else lurking beneath the surface?


Just because it is "spewing" 400 pounds(??? 1 That_Guy) of water per second right now, does not mean that it has always been losing water at that rate. Since it is evaporating and its evaporating area is responsible for the rate, there could be a feedback loop accelerating the process.

But even then, 440 pounds (which im guessing actually means 440 * 16 fluid ounces) isnt much compared to the mass Enceladus (~10^20kg).
SemiNerd
3 / 5 (2) Jun 22, 2011
"roughly 440 pounds of water vapor is lost every second."

Pounds are a measure of weight in a given gravitational environment, so is that 440 pounds as measured from earth, or 440 pounds as measured from Enceladus?

Technically, they should be using a unit of Mass (Such as a Kilogram) in order to clear up any confusion.

Just stirring the pot :)


1 pound = .454 Kg. Use the measurement of choice. Changing measurement units doesn't change what it is. Its still mass. What we call weight is just a measurement of an equal amount of mass in a 1g gravitational field.
that_guy
5 / 5 (1) Jun 22, 2011
@Semi - *sigh*. It was more of a joke to begin with. Pounds are a measure of weight, and grams(or kilos) are a measure of mass. Something that weighs 1 pound on the moon is approximately 3 kilos. Mass doesn't change, but weight does.

@FM - In seriousness, it sounds like they estimated 200KG, and converted it to pounds. I have actually heard scientists b*tch when someone tried to use the term pounds in a situation like this, because the term is *technically* relative to gravitational attraction rather than absolute mass.

@TKJ - I was thinking the exact same thing. I had one concern about the idea - What happens when the explorer craft finally gets to the water layer, and the ambient pressure goes from extremely low to deep ocean pressure. Will the water explode out of the hole? Will the craft have a mechanism to create more ice above it, sealing itself in? Will it be able to withstand the sudden change in pressure?
ubavontuba
1 / 5 (1) Jun 22, 2011
Questions: Where does the salt come from? Is there a water cycle?
tkjtkj
not rated yet Jun 22, 2011


@TKJ - I was thinking the exact same thing. I had one concern about the idea - What happens when the explorer craft finally gets to the water layer, and the ambient pressure goes from extremely low to deep ocean pressure. Will the water explode out of the hole? Will the craft have a mechanism to create more ice above it, sealing itself in? Will it be able to withstand the sudden change in pressure?


No problem there: as the capsule decends, water behind it will reform ice.. no 'blow-out' at all.
Your concerns with pressure, though are very valid .. i 've no idea how to address that!
zbarlici
5 / 5 (1) Jun 22, 2011
@grgfraiser
Agreed. Now if we could only figure out how to equip a lander that is capable drilling through 50 miles of ice, it would be a possibility.

Just land a nuke reactor on the ice and set it to "BAKON FRY MAX PWR SETTING"... & just for kicks maybe nasa can mount a little frying pan with some strips of bacon in it, that way they can feed the algae a delicious meal when the reactor breaches thru the last sliver of ice... Then realize that while they were too busy paying too much attention to frying pan mission detail, they`d forgot to substitute the reg. bacon with low-sodium.
RealScience
5 / 5 (3) Jun 23, 2011
Scientist Steve, tkjtj and fmfbrestel - no need to drill, or even to land - Enceladus is sending flash-frozen ocean samples to space for free. Orbit and collect salty ice grains.

NickFun: If Enceladus is losing 200 kg/sec, that's 6x10^9 kg/year.
If it had kept this up for the entire age of the solar system that would be ~2.5x10^19 kg, or 1/4 of Enceladus's current mass. Thus if (and that's a big if) this has gone on since the solar system settled down, Enceladus would only have to have started out 25% larger than it is now, even with no replenishment.

SemiNerd - from a common use perspective, you are correct.
But technically That_Guy is correct: the imperial unit of mass is a 'slug', and at Earth's 32 ft/sec2, a slug weighs 32 pounds (just as a kilogram at 9.8 m/sec2 weights 9.8 Newtons).
Yellowdart
3 / 5 (2) Jun 23, 2011
If it had kept this up for the entire age of the solar system that would be ~2.5x10^19 kg, or 1/4 of Enceladus's current mass. Thus if (and that's a big if) this has gone on since the solar system settled down, Enceladus would only have to have started out 25% larger than it is now, even with no replenishment.


It's not entirely water/ice though or its density would be less than 1.6g/cm^3 as well. So it's a bit misleading what you said.

The original mass of water available coupled with how Saturn's tidal forces effect the rate of water loss due to tidal pumping would be necessary to know.

Similar to taking more pumps in a super soaker the less water there is, more energy becomes required to expel it than originally with a full tank. So my guess is that the rate of water loss would a been higher in past as well.
Conner
2 / 5 (2) Jun 23, 2011
@Scientist_Steve et al: I don't think drilling is very viable in this situation. The reason the plumes exist in the first place is due to the rapid drop in pressure effectively pulling the liquid away from the planet: "The drop in pressure causes the liquid to evaporate into a vapor... which subsequently creates the plumes, the science team believes."

If we drilled/melted our way down, we would most likely leave a hollow hole behind the drilling mechanism unless we utilized some kind of capping system. However, keep in mind that some of these particles were moving at about 17.7 km/s, that would take a large pressure difference to accelerate the vapor to those speeds. We'd be talking about a very large, robust capping system. Our best bet would be (if we're trying to get into the actual water) to fire a probe into the actual tiger stripes, though again, retrieval/contamination would be problematic.
RealScience
5 / 5 (2) Jun 23, 2011
YellowDart - Yes, 1000 characters forced some simplifications

A density of 1.6 for an ice/rock mix means that Enceladus is more than half water even now, so treating it as essentially water/ice is not far off. The extra 25% would simply be all water, and its loss would help explain why Enceladus is denser than Saturn's other small moons.

I agree that the rate may have been far from constant (that's why I called keeping up a constant rate "a big if"). However if one assumes that its anomalously high density is from the loss of water leaving relatively more rock (probable), and the time span for the loss to be most of the age of the solar system (plausible), then the current loss rate is not far off (within a factor of two) of what the average would be.
GSwift7
1 / 5 (1) Jun 23, 2011
Agreed. Now if we could only figure out how to equip a lander that is capable drilling through 50 miles of ice, it would be a possibility


..and after traveling down through the 50 miles of ice, exploring the water, then drill back up through the 50 miles of ice to transmit the results back to Earth.
RealScience
not rated yet Jun 23, 2011
Why drill 50 miles down and back???
Enceladus is already spraying flash-frozen samples into space for free!
Scientist_Steve
5 / 5 (1) Jun 23, 2011
@everyone who commented on my original post
Sorry for my original wording. I wasn't actually trying to suggest that "drilling" to the ocean below was a viable option. It was meant to be a sarcastic comment : ) In reality, I was thinking of the same complications that many have listed above. Probably the biggest being as GSwift7 stated, even if you get down to the ocean, getting results back to the surface to transmit is pretty challenging and unlikely.
@Realscience
The problem with the flash frozen samples is that it will still be extremely difficult to directly detect any signs of life from them. Case in point, we have landers roaming the martian surface and still can't even confirm it there.
RealScience
not rated yet Jun 23, 2011
@Scientist Steve: Agreed that it is difficult, but it look a heck of a lot easier than melting our way 50 miles down on a far-off moon, then conducting a search, and then getting the data back.
A chemical analysis would be no harder with flash-frozen samples than with fresh samples. Many earth bacteria and archaea could survive being flash-frozen and then re-thawed so I suspect that primitive life living in salty slush on Enceladus could, too, and thus a biological analysis might not be harder either. And without having to land gently in a deep gravity well, it would be easier to send analysis equipment to Enceladus than to Mars.
For sure it is non-trivial, but the jets of salty ice grains make it the easiest of the plausible places to search for extraterrestrial life.
Scientist_Steve
not rated yet Jun 23, 2011
@Realscience
Oh hands down, I agree that we should try any method of detecting life before we try to land or drill or anything resembling it. Our first priority should definately be attempting to catch as much of the ejected frozen sample as possible. However, analysis may not be more difficult, but in order to "directly" detect any microbes (and squash every critic), you would need a perfectly intact specimen. One would hope that there was a very high concentration of microbes or other organisms in this ocean. Otherwise, I think the "needle in a haystack" might apply. But honestly, its difficult to speculate on that and I could be dead wrong. I am reminded of an article ( on here i believe) not long ago where they drilled a hole through an artic ice sheet. No one expected to see anything there either. I think it only took like an hour or something to find organisms.
Scientist_Steve
not rated yet Jun 23, 2011
@Realscience
Also, thats a good point about the gravity well. That would definately influence our ability to send better equipment.
RealScience
not rated yet Jun 23, 2011
@Scientist Steve: I agree that we can't count on life forms being as plentiful as they are in Earth's ocean (even they exist in Encedadus at all). But even at one millionth as common, they would still average one per gram of water, or ten per gram if one includes viruses.
If they are only a billionth as plentiful, the search would get harder - one per liter would be hard to detect, and I would guess that they would multiply more slowly due to the lack of an intense energy source like sunlight.

The energy density available per square meter is roughly 1/1,000,000 that available on the earth's surface, so for a wild guesstimate microbes growing 1/1000 as fast as earthly microbes (if they exist at all).
Yellowdart
1 / 5 (1) Jun 24, 2011
A fantastic article on this was written in Science American about 3 years ago.

http://www.angelf...0812.pdf

Page 26.

I wouldn't be surprised by other earth similarities like bacteria or archaea.

I wonder what a layer of subterranean water on the earth might do. The initial burst and probably only burst, might explain how Saturn ended up with Enceladus in the first place.
GSwift7
1 / 5 (1) Jun 29, 2011
Why drill 50 miles down and back???
Enceladus is already spraying flash-frozen samples into space for free!


The problem with the flash frozen samples is that it will still be extremely difficult to directly detect any signs of life from them.


Go to Yellowstone National Park. Take a sample of the water from Old Faithfull and see what kinds of signs of life there are. Or, go to the ocean and take a sample of ocean spray. Heck, ride on the back of a whale and get a sample of water when it blows up out of its blow hole. I'll bet you would still have a hard time finding evidence of life in the sample. You could literally be standing on top of life and not get any signs of it in a sample from a geological gieser.
Scientist_Steve
not rated yet Jun 29, 2011
@Gswift7
Well said. This is also my concern with the search for life anywhere. Unless you capture images of something thats indisputably life like a giant enceladus crab or something, confirming life in these places may be difficult for quite some time. Atleast until our technology significantly improves. Regardless, I hope we continue looking. Confirming the existence of life elsewhere would in my mind be the most important discovery ever. I hope it happens in my lifetime.
GSwift7
1 / 5 (1) Jun 30, 2011
confirming life in these places may be difficult for quite some time. Atleast until our technology significantly improves. Regardless, I hope we continue looking.


Learning how to look for life is where we are right now. As far as detecting life without actually traveling somewhere and taking a picture of it, we are at a stage comparable to astronomy before the telescope or biology before the microscope. We don't even know what tools we might need, much less having the skills to use those tools. We are still developing our skills with the telescope, even after all the centuries since we acquired it.

Discovery of life elsewhere might be a big deal, or not so much. If we find it on Mars and it's just like life here, then that's not so big. If we find it several light years away, that's a big deal. Or, if life on Mars is different, then that's a big deal too. Finding intelligent life would be unimaginable in its impact to our culture. Scary actually.

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