[X] My Assistant

[SigurRosFan]

Found at SpaceWeather:

--- Space artist Merry Wooten anticipated the discovery two decades ago:



Wooten had a hunch that Saturn's powerful tides might cause geothermal activity on Enceladus. Her painting of the resulting ice-geysers first appeared in a planetarium show, "When Worlds Erupt," in 1986. ---

I want more. Where are other Enceladus artists?

[ljk4-1]

Here is one from the NASA Cassini Web site made in the 1990s:

http://saturn.jpl.nasa.gov/multimedia/imag...cfm?imageID=603

And if someone could scan in pages 30-31 of the July, 1981 issue of
National Geographic Magazine to post here, you will see an even more
amazing "prediction" of Enceladus geysers.

[t_oner]

Here is a scan from page 30-31 of the July, 1981 issue of National Geographic Magazine. Painting by Lloyd K. Townsend © National Geographic Society.

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[David]

Here is a scan from page 30-31 of the July, 1981 issue of National Geographic Magazine. Painting by Lloyd K. Townsend © National Geographic Society.

And here's (part of) the text going with that picture:

Shining Enceladus

Mirror of the Solar System, Enceladus (right [generic image of Enceladus as a white ball]) reflects nearly all the light that reaches it. It may be that the satellite is continually being recoated from its interior (illustrated above [Townsend illustration]). One hypothesis is that tidal forces -- resulting from Saturn's and Dione's gravity --- heat its interior. This keeps the moon a giant drop of water with a thin ice crust that can fracture to emit ice crystals, which can escape to feed the very faint E ring.

Related text in the article:

Rich Terrile, one of the younger team members, is being grilled across the table about his ideas on Enceladus. There has been speculation that Enceladus could be caught in a tidal tug-of-war between Saturn and Dione. This tugging could be heating Enceladus' interior. The moon could be like a big drop of water coated with an ice crust, explaining why Enceladus is smooth. Like a glacier, the moon's thin crust would be mobile enough to fill in craters.

Terrile and another Voyager scientist, Al Cook, had noted earlier that Enceladus is at the brightest point in the outermost E ring. Terrile now is arguing that Earth-based infrared measurements indicate that the broad and dim E ring has mostly small particles. Terrile and Cook think that those particles could be coming off Enceladus.

"One meteorite puncturing the surface every thousand, or even ten thousand, yeaers could spray out enough ice crystals to supply the E ring," proposes Terrile. Ice volcanoes are also possible. The ring particles that either would produce could be coating Enceladus and neighboring Tethys. That coating might explain why both moons are exceptionally bright."

Just for historical context! It seems to me that Townsend was attempting to illustrate cryovolcanism, I guess, not geysers; and of course (as the illustration shows) it was imagined as happening all over the moon, due to an overall underlying liquid water layer.

[SigurRosFan]

Thanks for posting, Tayfun. Looks like frozen fountains.

[centsworth_II]

The JPL image looks like a gentle release of vapor and not the sort of thing that could reach 100's of km from the surface. The other two renderings look more artistic than realistic. I wonder if the jet of vapor would even be visible from the surface in "real life". I'd like to see an estimate of volume of flow and density for the jets.

[scalbers]

Perhaps a relatively low jet velocity is needed in the weak gravity of Enceladus? I'll have check if that is listed in the Science papers...

[SigurRosFan]

Enceladus' escape speed: 0.25 km/s

--- Most of the ice seen erupting in plumes falls back to the surface, but about 1 percent escapes and contributes to Saturn's E ring. ---

[ljk4-1]

Here is a scan from page 30-31 of the July, 1981 issue of National Geographic Magazine. Painting by Lloyd K. Townsend © National Geographic Society.

I don't normally like to post just thank you notes without something
of technical value behind them, but I have to say - THANK YOU Tayfun
for doing this and thank you David for the text!

Indeed it is of historic value, not to mention bringing back lots of
fond memories.

[edstrick]

"Geezers on Enceladus"

(Retirement home for planetolgists?)

[tty]

Enceladus' escape speed: 0.25 km/s

--- Most of the ice seen erupting in plumes falls back to the surface, but about 1 percent escapes and contributes to Saturn's E ring. ---

How does this tally with the "sublimation off warm ice" theory? Wouldn't it require that the vapor is expelled with some pressure for even 1 % to reach 0.25 kms-1?

tty

[centsworth_II]

Enceladus' escape speed: 0.25 km/s

--- Most of the ice seen erupting in plumes falls back to the surface, but about 1 percent escapes and contributes to Saturn's E ring. ---

Wow, really low escape speed -- by earthly standards. And almost all of it still falls back to the surface?! So maybe the gentle waft of vapors in the NASA image is accurate. Now to reconcile this with the Cassini images which have a jet-like quality to them rather than the thin, wispy layers (as in some Titan limb images) that I would expect of a slowly rising mist.

[Thorsten]

Hello everybody,

Inspired by these great pieces of artwork I recently tried to make a crude drawing of the geysers of Enceladus. Probably not very accurate, though.

[Guest_PhilCo126_*]

Nice work ... Nice topic

[Bill Harris]

That escape velocity is still 900 km/h or 560 mph, which is pretty quick. Once we know more about rates and volumes we can make estimates of the pressures involved.

--Bill

[scalbers]

The artwork in post #1 is nice in showing sheetlike eruptions suggestive of linear "stripes". Also reminds me of some linear lava fountains in Hawaii.

The Enceladus escape velocity of 250m/s might compare with a 50m/s velocity in Old Faithful Geyser. Perhaps consistent if only 1% reaches an outlier escape velocity. Or would a water geyser have a more explosive power against the cold vacuum of space, compared to one against the warmer atmosphere of the earth environment?

[helvick]

That escape velocity is still 900 km/h or 560 mph, which is pretty quick. Once we know more about rates and volumes we can make estimates of the pressures involved.

Which if my calculations are right would be enough to loft some water ~3200m on earth if we had no atmosphere to worry about. Some back of the envelope drag calculations lead me to believe that it would be lower than ~630m once you factor that in, probably a lot less since that's almost supersonic and I can't see a column of water maintaining any sort of integrity under those forces.

In any case these are pretty mean fountains, even if Enceladus is kinda small it takes a lot of oomph to kick something up at 250m/sec.

[Bob Shaw]

Which if my calculations are right would be enough to loft some water ~3200m on earth if we had no atmosphere to worry about. Some back of the envelope drag calculations lead me to believe that it would be lower than ~630m once you factor that in, probably a lot less since that's almost supersonic and I can't see a column of water maintaining any sort of integrity under those forces.

In any case these are pretty mean fountains, even if Enceladus is kinda small it takes a lot of oomph to kick something up at 250m/sec.

If you have a mass of water being ejected upward, is there any chance of a kick being given by the water which follows the initial surge? I'm thinking of a snowball being ejected on top of a boiling fire-hose. Such a combination might cause a proportion of the material to reach escape velocity...

Bob Shaw

[helvick]

If you have a mass of water being ejected upward, is there any chance of a kick being given by the water which follows the initial surge? I'm thinking of a snowball being ejected on top of a boiling fire-hose. Such a combination might cause a proportion of the material to reach escape velocity...

I don't see how unless what is being ejected has a very high percentage of dissolved gases that can subsequently cause a solid block of ice to explode. That would add some "boost" to a percentage of the material. The dynamics of that seem a bit unlikely to me.

I've been trying to think how this would actually work. All I can come up with is that the sources are much more like rift volcanic eruptions than anything we are familiar with involving water\ice. In that case the ejecta would be some mix of mostly ice, some rapidly cooling water and the various dissolved gases.

The fact that what has been detected is seemingly a uniform "cloud" of very small particles would indicate that that is not the case.

[ugordan]

There's also one important factor to consider. Water vapor ejected from the geysers doesn't have to move some 250 m/s to get a chance of escaping. Water molecules at 0 degrees Celsius have a substantial thermal kinetic energy as well and that alone can probably overcome the escape velocity. Some back of the envelope calculations could easily come up with an average speed of a water molecule at a given temperature.

Now, how that translates into macroscopic behavior of larger ice particles I don't know (Brownian motion?). But clearly individual (gas) particles have a very fair chance of escaping into the E ring, regardless of vent exhaust velocities.

The fact the plumes look pretty colimated implies they are kicked up at an appreciable speed. Either that or the water is really pretty cold so the molecules diffuse slowly.

[helvick]

Water molecules at 0 degrees Celsius have a substantial thermal kinetic energy as well and that alone can probably overcome the escape velocity. Some back of the envelope calculations could easily come up with an average speed of a water molecule at a given temperature.

Forgot about that aspect.
Google threw up this snippet (which is searchable by us plebs but not accessible - drat)

Enceladus' Water Vapor Plume -- Hansen et al. 311 (5766): 1422 ...
Note that v is well above the 24000 cm/s escape velocity. The flux is thus at least S = 5 x 1027 ... At 180 K, the thermal velocity v is 46000 cm/s. ...

That seems to hint that the thermal velocity is almost double the escape velocity. Then again the missing bits in that quote might say something completely different but the implication is that the thermal velocity significantly exceeds escape velocity.

Makes sense, otherwise it would have a noticablel atmosphere.

[scalbers]

The well collimated jets within the larger plume might extend upward around 50km. This might be a good value to plug into a ballistic trajectory calculation with Enceladus' gravity. I'll still have to look for the numbers, though I'd suspect they'd be consistent with a Yellowstone geyser type of eruption.

[mars loon]

Quite an amazing and beautiful prediction in these artworks.

Inspiring new work by Thorsten. I hope you will refine it further with time.

ken

[SigurRosFan]

Hello everybody,

Inspired by these great pieces of artwork I recently tried to make a crude drawing of the geysers of Enceladus. Probably not very accurate, though.

Thorsten, great drawing! I'm looking for exactly such impressions.

More!

[ljk4-1]

Does anyone remember if Sky & Telescope, Astronomy, Scientific American,
or some other publication of the time had their own artist's interpretations of
Enceladus as seen by Voyager 1 (but before Voyager 2)?

[JRehling]

Forgot about that aspect.
Google threw up this snippet (which is searchable by us plebs but not accessible - drat)

That seems to hint that the thermal velocity is almost double the escape velocity. Then again the missing bits in that quote might say something completely different but the implication is that the thermal velocity significantly exceeds escape velocity.

Makes sense, otherwise it would have a noticablel atmosphere.

That thermal velocity assumed a temp of 180K... presumably the H2O is >273K at launch, though the highest validated surface temperature is 145K. I guess 180K is a split-the-difference number chosen without principle?

When it comes to planning a possible sample return, it would be interesting to theoretically constrain what the nature of the plumes is. Is it so dispersed that it consists of isolated molecules lacking any phase, or is it tiny ice particles, and of what size?

If that water has monocellular life in it, how would it be represented in the plume -- flash-frozen in ice particles -- and if so, feasibly in high enough concentration to hope for a sample?

[Thorsten]

Does anyone remember if Sky & Telescope, Astronomy, Scientific American,
or some other publication of the time had their own artist's interpretations of
Enceladus as seen by Voyager 1 (but before Voyager 2)?

I couldn't find anything! On the other hand, there were only eight month in between the two Voyagers. As far as I can remember Voyager1 was quite far away from Enceladus at closest approach (something like 650'000 km) and showed only very little surface details, allowing a lot of artistic freedom. I think this might be the reason why Townsend was illustrating something like cryovolcanism in the July, 1981 issue of National Geographic Magazine (1 month before Voyager 2), instead of geysers and why this remodelling was happening all over the moon.

Anyway, a great topic!

[scalbers]

The well collimated jets within the larger plume might extend upward around 50km. This might be a good value to plug into a ballistic trajectory calculation with Enceladus' gravity. I'll still have to look for the numbers, though I'd suspect they'd be consistent with a Yellowstone geyser type of eruption.

Some quick calculations here, we might want to check elsewhere to see how this holds up. Assuming g=.113m/s^2 at the surface of Enceladus and neglecting the dropoff in gravity as we go up I get the following: A 50m/s Old Faithful type geyser would shoot up about 11km. To reach a plume height of 50km, we'd have to slightly more than double the ejection velocity to 106m/s.

[centsworth_II]

My Photoshop Elements rendition of how a lander might view the plumes from a safe distance.

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[ugordan]

My Photoshop Elements rendition of how a lander might view the plumes from a safe distance.

Nice, but why the blue sky?

[centsworth_II]

Nice, but why the blue sky?

Oops! I keep my monitor dark -- it looked black to me.

[helvick]

Oops! I keep my monitor dark -- it looked black to me.

Well won't there be some sort of semi localised atmosphere resulting from these plumes? And if so would that result in some sort of sky colour? Or are we talking about such minute quantities that it would never be visible?

[scalbers]

Good question about how much gas vs particles. In addition, the sky as viewed from the right vantage point might show some interesting halo effects similar to what we get with ice crystals on Earth (and Mars).

[tty]

There's also one important factor to consider. Water vapor ejected from the geysers doesn't have to move some 250 m/s to get a chance of escaping. Water molecules at 0 degrees Celsius have a substantial thermal kinetic energy as well and that alone can probably overcome the escape velocity. Some back of the envelope calculations could easily come up with an average speed of a water molecule at a given temperature.

Now, how that translates into macroscopic behavior of larger ice particles I don't know (Brownian motion?). But clearly individual (gas) particles have a very fair chance of escaping into the E ring, regardless of vent exhaust velocities.

The fact the plumes look pretty colimated implies they are kicked up at an appreciable speed. Either that or the water is really pretty cold so the molecules diffuse slowly.

I don't see how thermal motion could create such fairly well colimated plumes since it is by definition random. To my mind this suggests that the plumes contains a fairly large proportion of particles large enough not to be strongly affected by collisions with stray molecules.
Still it is of course possible that the part of the material that escapes from Enceladus is largely the highest velocity molecules. . As the plumes thin out the free path will increase until at least some molecules escape while the larger stuff falls back as "snow".
An interesting question is whether "snowflakes" falling back on Enceladus on a ballistic trajectory have enough kinetic energy to melt on impact. Some back-of-an-envelope (literally) calculation says "No".

tty

[centsworth_II]

I'm wondering if the plumes, seen from the surface, would be impressive towers of water, or would they be tenuous?

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[scalbers]

Perhaps they'd be a bit on the tenuous side as they only (so far) appear to show up in high phase angle imaging. This is even true for some fairly high resolution images. It might be worth checking though if there are any high resolution lower phase angle views with the tiger stripes right on the limb.

BTW, the CNN web video story on this shows Torrence Johnson and some animated artwork that seems reasonable in appearance.

[remcook]

Not sure if it's enceladus, but looks pretty funky. Note the astronauts ;-)

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[Bob Shaw]

Not sure if it's enceladus, but looks pretty funky. Note the astronauts ;-)

It looks like one of David A Hardy's paintings from 'The Challenge of the Stars'.

Bob Shaw

[nprev]

That's a Chesley Bonestell painting....I recognize it by the way that he painted Saturn, and it's supposed to be the surface of Titan (notice the green horizon glow from the presumed--at that time--thin methane atmosphere). Is this from Willy Ley's The Conquest Of Space?

[Michael Capobian...]

Notice that for Saturn's rings to be almost parallel to the horizon, as they are in that painting, you have to be near one of the poles.

Michael

[nprev]

Notice that for Saturn's rings to be almost parallel to the horizon, as they are in that painting, you have to be near one of the poles.

Michael

Is that true? I thought Titan's orbit was coplanar with the rings, and that its axial inclination is nearly zero wrt Saturn...if so, I'd expect the rings to look practically edge-on and level to the horizon from almost any point on Titan's surface.

However, the low elevation of Saturn with respect to the horizon does imply that the scene is set at a high latitude...whether north or south, I can't tell!

[David]

Is that true? I thought Titan's orbit was coplanar with the rings, and that its axial inclination is nearly zero wrt Saturn...if so, I'd expect the rings to look practically edge-on and level to the horizon from almost any point on Titan's surface.

However, the low elevation of Saturn with respect to the horizon does imply that the scene is set at a high latitude...whether north or south, I can't tell!

The fact that Saturn is close to the horizon only tells us that the site is close to one or the other edge of the sub-Saturnian hemisphere, where it will stay permanently, of course.
The angle of the rings tells us that we're at a high latitude: if the rings are straight up and down like this (|) then you're at the equator; if the rings are horizontal, you're at the N or S pole. These fellows must be at about 75° N or S; the longitude is a little harder to figure, but I guess around 60° or 300° (i.e., either 75 N, 300, or 75 S, 60)
But it can't be Enceladus, because Saturn is far too small. If not Titan, it could be Rhea perhaps.

Anyway, it is a cute thing about these pictures that they almost always show Saturn (or Jupiter) in the sky, and so you can pretty much figure out exactly where such a picture could be taken!

[Michael Capobian...]

But it can't be Enceladus, because Saturn is far too small. If not Titan, it could be Rhea perhaps.

Well, that depends on the focal length of the artist's "lens," which you can never know for sure in a painting.

Michael

[David]

Well, that depends on the focal length of the artist's "lens," which you can never know for sure in a painting.

Michael

On Earth that would be true; but on Enceladus, that changes two things: one, Saturn occupies such a large portion of the sky that you have to get considerably closer to 0° longitude in order to get Saturn that high in the sky; and if you enlarge your field of view so that Saturn appears that size, you are going to find yourself with a very noticeably curved horizon -- if you don't end up with all of Enceladus inside your frame! Enceladus is really a very small world.

[ljk4-1]

Found this artwork of an Enceladian geyser as depicted by Brian Smallwood:

http://www.firstinspired.com/spaceprime/space/Encelad.htm


I also like his depiction angle of Olympus Mons:

http://www.firstinspired.com/spaceprime/space/olympus.htm

[SigurRosFan]

There's another great vision:

- http://antwrp.gsfc.nasa.gov/apod/ap060608.html

Enceladus' Geysers by Michael Carroll (full resolution 498 KB):

[volcanopele]

WOW! That's the best I've seen to date. You can definitely see the linear nature of the vent(s), as opposed to a few others I have seen (even done recently).

[ljk4-1]

This is space artist Joe Bergeron's interpretation of the Geysers of Enceladus:

http://homepage.mac.com/joebergeron/enceladus.htm

[David]

The artistic license in these pictures consists of putting the plumes at much lower latitudes than they are actually found. At the south pole of Enceladus, Saturn should be right on the horizon -- half under, half over. And it would appear even larger than it appears in these pictures.

[ljk4-1]

The artistic license in these pictures consists of putting the plumes at much lower latitudes than they are actually found. At the south pole of Enceladus, Saturn should be right on the horizon -- half under, half over. And it would appear even larger than it appears in these pictures.

Maybe they are capturing Enceladus in the midst of its rolling over -
and the jets have temporarily pushed the moon further from Saturn.

[alan]

Boosting the Signal
This color-coded image was processed to enhance faint signals, making the contours and extent of the fainter, larger-scale component of the plume easier to see.

http://saturn.jpl.nasa.gov/multimedia/imag...fm?imageID=2211