Saturn's moon Enceladus spreads its influence

Sep 22, 2011
Water vapor and ice erupt from Saturn's moon Enceladus, the source of a newly discovered donut-shaped cloud around Saturn. Image NASA.

(PhysOrg.com) -- Chalk up one more feat for Saturn's intriguing moon Enceladus. The small, dynamic moon spews out dramatic plumes of water vapor and ice -- first seen by NASA's Cassini spacecraft in 2005. It possesses simple organic particles and may house liquid water beneath its surface. Its geyser-like jets create a gigantic halo of ice, dust and gas around Enceladus that helps feed Saturn's E ring. Now, thanks again to those icy jets, Enceladus is the only moon in our solar system known to influence substantially the chemical composition of its parent planet.

In June, the European Space Agency announced that its Herschel Space Observatory, which has important NASA contributions, had found a huge donut-shaped cloud, or torus, of vapor created by encircling Saturn. The torus is more than 373,000 miles (600,000 kilometers) across and about 37,000 miles (60,000 kilometers) thick. It appears to be the source of water in Saturn's .

Though it is enormous, the cloud had not been seen before because is transparent at most of light. But Herschel could see the cloud with its infrared detectors. "Herschel is providing dramatic new information about everything from planets in our own solar system to galaxies billions of light-years away," said Paul Goldsmith, the NASA Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The discovery of the torus around Saturn did not come as a complete surprise. NASA's Voyager and Hubble missions had given scientists hints of the existence of water-bearing clouds around Saturn. Then in 1997, the European Space Agency's confirmed the presence of water in Saturn's upper atmosphere. NASA's Submillimeter Wave Astronomy Satellite also observed water emission from Saturn at far-infrared wavelengths in 1999.

While a small amount of gaseous water is locked in the warm, lower layers of Saturn's atmosphere, it can't rise to the colder, higher levels. To get to the upper atmosphere, must be entering Saturn's atmosphere from somewhere in space. But from where and how? Those were mysteries until now.

Build the model and the data will come.

The answer came by combining Herschel's observations of the giant cloud of water vapor created by Enceladus' plumes with computer models that researchers had already been developing to describe the behavior of water molecules in clouds around Saturn.

One of these researchers is Tim Cassidy, a recent post-doctoral researcher at JPL who is now at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder. "What's amazing is that the model," said Cassidy, "which is one iteration in a long line of cloud models, was built without knowledge of the observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren't expecting such detailed 'images' of the torus, and the match between model and data was a wonderful surprise."

The results show that, though most of the water in the torus is lost to space, some of the water molecules fall and freeze on Saturn's rings, while a small amount -- about 3 to 5 percent -- gets through the rings to Saturn's atmosphere. This is just enough to account for the water that has been observed there.

Herschel's measurements combined with the cloud models also provided new information about the rate at which water vapor is erupting out of the dark fractures, known as "tiger stripes," on Enceladus' southern polar region. Previous measurements by the Ultraviolet Imaging Spectrograph (UVIS) instrument aboard the showed that every second the moon is ejecting about 440 pounds (200 kilograms) of water vapor.

"With the Herschel measurements of the torus from 2009 and 2010 and our cloud model, we were able to calculate a source rate for water vapor coming from Enceladus," said Cassidy. "It agrees very closely with the UVIS finding, which used a completely different method."

"We can see the water leaving Enceladus and we can detect the end product -- atomic oxygen -- in the Saturn system," said Cassini UVIS science team member Candy Hansen, of the Planetary Science Institute, Tucson, Ariz. "It's very nice with Herschel to track where it goes in the meantime."

While a small fraction of the water molecules inside the torus end up in Saturn's atmosphere, most are broken down into separate atoms of hydrogen and oxygen.
"When water hangs out in the torus, it is subject to the processes that dissociate water molecules," said Hansen, "first to hydrogen and hydroxide, and then the hydroxide dissociates into hydrogen and atomic oxygen." This oxygen is dispersed through the Saturn system. "Cassini discovered atomic oxygen on its approach to Saturn, before it went into orbit insertion. At the time, no one knew where it was coming from. Now we do."

"The profound effect this little moon Enceladus has on Saturn and its environment is astonishing," said Hansen.

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User comments : 13

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kevinrtrs
1.5 / 5 (15) Sep 22, 2011
So the obvious question doesn't get addressed:
How is it possible for this little moon to still be spraying its environment with vapour after supposed billions of years? Where does the moon get it from? Does it manufacture it out of nothing, since it's obviously leaking out of the system at a high rate?
It's really astonishing to the researchers that the little moon is still active - after "Billions of years" but they're not saying anything about that. Maybe it's because it brings up the other decidedly uncomfortable possibility: Enceladus is still a very young moon - less than 10 000 years old.
vidar_lund
3.7 / 5 (6) Sep 22, 2011
Enceladus is still a very young moon - less than 10 000 years old.

Yeah, Sarah Palin told me it's 6000 years old so it must be true.
Pavel-chemist
5 / 5 (5) Sep 22, 2011
Even if we assume that this moon spew it's material at the same rate all 4.5 billion years (that is may well be not the case) we have:
200kg*(3600*24*365*4,5e9)s = 2,84e19 kg/4.5 Gy
Enceladus's mass 1.1e20 kg
ratio: 0.26
so, it will be nearly one fifth of it's total initial mass.
So, this is obviously beats your "young earth (Universe) theory".

Also, there are suggestions, that Enceladus had not always had such activity and there are was calm periods in its history (sorry, I missed a link). Therefore mass loss was less than one fifth of initial mass.
javjav
1 / 5 (3) Sep 22, 2011
All this water going out could be letting a big empty space under the ice cover, I am wondering if this space is partially filled with water vapor, thus creating an internal atmosphere over the inner sea. Looking at the geysers they could create a lot of turbulence under their roots, which could produce winds, sea waves, clouds, rain, and icebergs floating over the inner sea, all under a sky of solid ice illuminated by storm lightings. Just wondering...
barakn
1 / 5 (1) Sep 22, 2011
Did Kevin simply not read the article and therefore not see the mass loss rate estimate of 200 kg/s, or is he so mathematically illiterate that he didn't know he could use that and the mass of the moon to figure out how long it would take to disappear?
Robert_Wells
4 / 5 (4) Sep 22, 2011
Did Kevin simply not read the article and therefore not see the mass loss rate estimate of 200 kg/s, or is he so mathematically illiterate that he didn't know he could use that and the mass of the moon to figure out how long it would take to disappear?


nah, he didn't. Kevin likes to read an article til he finds something that he can 'jump' on and then he stops reading and scrolls down to the posts section and spams his young earth nonsense. the math is simple enough for a high school physics student to work out on his own, but Kevin never made it past 8th grade church school where nuns beat nonsense into him over those years. wish we could save him but he never sticks around after posting, he doesn't want to be saved
kevinrtrs
1.7 / 5 (6) Sep 22, 2011
Who said anything about the moon disappearing because of a loss of vapour? Just how must water do you suppose that body has in it? And where exactly does such a large amount of water come from?
Furthermore, where does the energy come from that keeps it going for 4.5 billion years?
As for the suggestions that it wasn't active all the time, please do elaborate on those - we'd all like to know just how that idea came about so we can all evaluate it on its merits.
nkalanaga
5 / 5 (5) Sep 22, 2011
Orbital eccentricity changes constantly. When it's less eccentric, there's less heating, so less water loss. When the eccentricity increases, so does the heating, and the loss. That is a normal process for any orbital system involving more than two objects.
Robert_Wells
5 / 5 (3) Sep 22, 2011
Furthermore, where does the energy come from that keeps it going for 4.5 billion years?


WOW, kevin responded! i never thought i'd see the day.

but yea ever heard of tidal heating?
http://en.wikiped..._heating

im so amazed that you responded in anyway that im not going to mark that as low(gave you a 3 just because you responded) , at least your engaging in conversation(limited as it is), its a step closer to your redemption.

as for how much water Enceladus contains, i'll let someone more inclined answer that instead of showing off my limited math skills.
Life_is_like_that
1 / 5 (2) Sep 22, 2011
10,000 years young seems an odd and arbitrary position to take. Since orbital mechanics are not mentioned in this article one can speculate that perhaps Enceladus formed further out and has been getting closer over the eons....or as others above have speculated orbital harmonics periodically (10s or 100s of thousands of years) increase internal heat enough to outgas and we (luckily) are technologically advance enough at this moment in time to witness the event.

In any case one must think in much greater time periods than 10,000 years as far as geological/planetary processes are concerned.
javjav
2 / 5 (1) Sep 22, 2011
Why do you think that this moon had less activity in the past? Simple thermodynamic math tell us is that this moon was much more active in the past, because there was a higher pressure inside it. It has been bleeding for a long time and the internal pressure has been decreasing for millions of years, what we see now is (probably) it's last breath.
RealScience
5 / 5 (1) Sep 22, 2011
keveinrtrs - The outer planets and their moons formed far enough from the sun that it was cold enough that the material they formed from never lost its water.
Water is very common out there; these moons have much more water than the inner worlds (as evidenced by their low density).

The energy is tidal energy.

Try looking at Wikipedia - it has answers to basic questions such as these.

And by the way, try doing a similar calculation on how much water the earth's air can hold to produce rain - nowhere near enough for the flood that you seem to believe covered the earth. And where did all of that water go?
Do a bit of math and you'll see how your interpretation doesn't add up.
frenchie
5 / 5 (1) Sep 23, 2011
@Kevin

At high temperatures and pressures, such as in the interior of giant planets, it is argued that water exists as ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and at even higher pressures as superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice.[13]

direct paste from wikipedia....wanna do research or do you have adverse reactions to critical thinking?