[X] My Assistant

[jsheff]

Enceladus just jumped to way near the top of the list of biologically interesting places. We know how to get to Mars; we some ideas of further exploration of Euiropa and Titan. Has anyone designed a mission to land on Enceladus? What would it take? How much delta vee?

[Jyril]

Enceladus has been near the top of the list since the discovery of its young surface. See for example The Nine Planet's list of best places for life (on December 19, 1996). I believe the original list is from 1995.

PS. I suggest you visit the main page of TNP too...

[Guest_Richard Trigaux_*]

"liquid water" seems a little bit exagerated for now, we don't know yet what takes place on Enceladus. But it is not possible anyway.

An interesting feature on Enceladus is that it is likely to contain a core of organic matter (comet-like). Most of the saturnian icy moons seems to be made of the same comet stuff, differenciated when they melt at time of accretion. So they are likely to all contain a carbon core with a pure ice mantle. (in the case of Phoebe, it would have be stripped of its ice mantle, due perhaps to its opposite rotation).


So if there is water into Enceladus (and there is probably water) it may soak a core of carbon and organic matter. A very interesting place to start a life chemistry, and perhaps life itself. But it would not go very far, by lack of energy. Heat is the only energy source, and it much varied with time, lefting perhaps Enceladus core completelly frozen at times, perhaps boiling at other times. Also the evolution from life chemistry to bacteria involves, as far as we know, a great mobility of proto-bacteria. How could water soaking a sandy core be mobile enough? Chance, if the core is made of carbon, it cannot melt, and if soaked with water anyway its temp cannot rise very much. So it must keep its sandy/dusty composition, not plain rock.

Perhaps the best method to know what happens into Enceladus core would be to visit Phoebe. I hear too of black dots which would mark the vents where steam goes out. But it is not sure at all that this black matter arises from the core. It could be gases. But if water arrives near the surface, it must bear evidences of what chemistry (or life) takes place into the core.

[ljk4-1]

I distinctly remember the National Geographic Magazine issue from 1981
which had an article on Voyager 1's mission to Saturn in late 1980 (but not
Voyager 2's later flyby, which had not happened yet).

Enceladus was rather far from Voyager 1 and no real surface features
could be seen.

This famous montage of the Saturn system includes the Voyager 1
image of the moon where you can see it is essentially blank:

http://photojournal.jpl.nasa.gov/jpeg/PIA01482.jpg

And Phil Stooke's more detailed maps and images:

http://www.ssc.uwo.ca/geography/spacemap/enceladu.htm

Scientists speculated that Enceladus' entire surface was
constantly being covered and reshaped by active geysers. The article
even included an artwork depicting these geysers spraying liquid water
from cracks in the crust!

Anyone else remember this or have the actual art handy to post?

[Decepticon]

I remember that picture!

I saw it in National Geographic Magazine, The 1981 issue.

[jmknapp]

Here's the Science magazine intro:

Tiger, Tiger, Burning Bright

[lyford]

Interview with Dr. Carolyn Porco
JPL Podcast

[David]

I distinctly remember the National Geographic Magazine issue from 1981
which had an article on Voyager 1's mission to Saturn in late 1980 (but not
Voyager 2's later flyby, which had not happened yet).

Scientists speculated that Enceladus' entire surface was
constantly being covered and reshaped by active geysers. The article
even included an artwork depicting these geysers spraying liquid water
from cracks in the crust!

Anyone else remember this or have the actual art handy to post?

I have that magazine! Sitting right where I can see it, in fact.

Unfortunately, I don't have a color scanner.

[nprev]

Enceladus just jumped to way near the top of the list of biologically interesting places. We know how to get to Mars; we some ideas of further exploration of Euiropa and Titan. Has anyone designed a mission to land on Enceladus? What would it take? How much delta vee?

In at least two respects, Enceladus now appears to be a much easier target than Europa as far as UMSF life seaches go: the crust apparently isn't nearly as thick, and the radiation environment is much more benign. Maybe the more expensive delta vee considerations would be more than offset by savings in lander/diver(?) design...

[tasp]

In at least two respects, Enceladus now appears to be a much easier target than Europa as far as UMSF life seaches go: the crust apparently isn't nearly as thick, and the radiation environment is much more benign. Maybe the more expensive delta vee considerations would be more than offset by savings in lander/diver(?) design...

Perhaps a craft could use Titan (as Cassini is) for orbit shaping. Several encounters could be set up to 'crank down' the orbit to graze Enceladus and Titan at apogee and perigee.

This would still leave the craft with a considerable velocity in the vicinity of Enceladus to 'burn off' though.

Would a ballute work in a water vapor plume at an altitude of 10 km? Every pass at Enceldaus would lower the apogee of the orbit (and the subsequent approach speed to Enceladus next time around) a bit, and you just keep grazing the plumes with your ballute till the approach speed is something your propulsion system can handle for either orbiting Enceladus or landing on it.

Note:
I don't have the figures handy but I seem to recall the equvalent of the Hill sphere of Enceladus (in reference to Saturn, not the sun) is quite small (Mimas's is miniscule). Perhaps useful studies might be feasible from an orbit that encounters Enceladus resonantly, or perhaps there is a slick way to get into a Lagrange orbit of some kind . . . .


How 'fluffy' is the surface? Maybe Enceladus is the one object in the solar system where 'lithobraking' is feasible.

{that last one may not be too serious, but if feasible, I claim priority}

[David]

Perhaps a craft could use Titan (as Cassini is) for orbit shaping. Several encounters could be set up to 'crank down' the orbit to graze Enceladus and Titan at apogee and perigee.

This would still leave the craft with a considerable velocity in the vicinity of Enceladus to 'burn off' though.

Would a ballute work in a water vapor plume at an altitude of 10 km? Every pass at Enceldaus would lower the apogee of the orbit (and the subsequent approach speed to Enceladus next time around) a bit, and you just keep grazing the plumes with your ballute till the approach speed is something your propulsion system can handle for either orbiting Enceladus or landing on it.

They'd have to put the lander in a very exact spot, though, wouldn't they? Most of Enceladus is not that interesting, and the interesting spots are pretty small, and we don't know their geography terribly well yet. Land something a kilometer from the hot spot and you might get nothing.

[tasp]

How 'fluffy' is the surface? Maybe Enceladus is the one object in the solar system where 'lithobraking' is feasible.

Whoa!

How 'fluffy' is the surface?

Probably VERY fluffy.

Low grav, micro-snow flakes, it could be 'fluffy' really deep. Like kilometers.

Is H2O 'fluff' a better insulator than vacuum? Is that why despite its' small size, Enceladus is warm inside?

And that it is warmest where the most 'fluff' is? Around the geyser region? Fluff melts from underneath when it gets 'too' warm, and gets thicker when heating effect wanes. It might be self regulating over a wider range (and to far lower BTU inputs) than anyone thought. Even a minor heat source; a small resonance effect, or waning radioisotope heating might work if the 'R' factor of the surface materials is good enough.

[nprev]

They'd have to put the lander in a very exact spot, though, wouldn't they? Most of Enceladus is not that interesting, and the interesting spots are pretty small, and we don't know their geography terribly well yet. Land something a kilometer from the hot spot and you might get nothing.

Does anybody have a surface gravity value for Enceladus? I would be quite surprised if it exceeds 0.02G, and if that intuition is correct then even a fairly massive lander could conceivably still be made quite mobile...

Of course, if tasp's "fluffy" model is correct then the whole thing might just sink & be lost forever...better drop some cheap toys to check things out before launching an Enceladean version of MSL...

[mchan]

How 'fluffy' is the surface? Maybe Enceladus is the one object in the solar system where 'lithobraking' is feasible.

{that last one may not be too serious, but if feasible, I claim priority}

Hmm, if the surface is like a field of fresh-fallen snow, how about 'ski-braking'? Hand waving -- put something like pontoons on the spacecraft and a control system with radar and pressure-on-pontoon feedback to manage the force of contact with the surface. Drop it in with a surface grazing orbit. It would help to know there are no big rocks, ridges, or crevasses along the 'landing strip'.

[vexgizmo]

James Oberg Chimes in:


Let Us Drink from the Fountains of Enceladus

[nprev]

James Oberg Chimes in:
Let Us Drink from the Fountains of Enceladus

Interesting idea. However, I do have to wonder if highly volatile Enceladus plume samples collected in an aerogel matrix would survive a return trip of presumably at least five years duration, to say nothing of microscopic Enceladeans...

[Guest_BruceMoomaw_*]

They would if you kept 'em cold enough after collection (or at least many of the complex biochemical molecules would).

It really would fit the kind of perverse sense of humor that God seems to possess if this pissant little ball of ice turned out to be the only other world in the Solar System with life...

[Guest_Richard Trigaux_*]

James Oberg Chimes in:
Let Us Drink from the Fountains of Enceladus

Jame's idea is a genius stroke: to use Stardust-like aerogel dust collectors to get samples of Enceladus plume, including eventual life chemistry and even life particules.

With this, no need of complex manoeuvers and landing, just some passes through the plume, as low as possible from the ground, and back to Earth with nearby intact samples.

At least, such a mission could be a preleminary for an actual landing, if it manages to take close images of the vents. Indeed a lander will need to know exactly where the vents are, and be able to squeeze in in order to get samples.


Oberg's idea looks like the easiest way to capture otherworldly biochemistry, and eventually life particules.

Enceladus water is not some ammonia eutectics, as expected on Titan (we are sure for this, there is no ammonia in the plume). It likely don't contain heavy sulphuric acid like expected on Europa (if so, it would not evaporate so easily).

Likely, most icy moons around Saturn have a comet-like composition, mainly ice and carbon materials. But they all melt at their formation (except the smallest like Hyperion and smaller) so that they differenciated between a white mantle of nearby pure ice and a black core of carbon materials. This core never melt, because carbon don't melt easily, and anyway it is soaked with water so that all the ice should evaporate before the core melts. (Phoebe would had had the same structure, but it was later stripped off its ice mantle). So, very likely, Enceladus core is a dust (not rock-hard) of carbon particules soaked with water (At times frozen, at times boiling, depending on the availability of gravitational flex heating).

So Enceladus core is very likely to contain an active pro-life chemistry, and eventually primitive forms of life. But we cannot expect too much: the early evolution of life heavily relies on the mobility of pro-cells and their hability to strive into great numbers into large spaces. A watertable is not so propicious! So what we may expect to find would be pro-cells, vesicles containing self-catalytic molecules (formed with amino acids and nucleic acids) but not DNA or RNA. But that only one of these vesicles is captured by an aerogel would tell us invaluable things on our own origins...

Hmm, if the surface is like a field of fresh-fallen snow, how about 'ski-braking'? Hand waving -- put something like pontoons on the spacecraft and a control system with radar and pressure-on-pontoon feedback to manage the force of contact with the surface. Drop it in with a surface grazing orbit. It would help to know there are no big rocks, ridges, or crevasses along the 'landing strip'.

There are blocks everywhere. Anyway, at a satellite speed, the contact even with a very soft material would be supersonic and result into an explosion.


Eventually if we find a planet made of aerogel, a probe could land on it head on, without any braking...

[ugordan]

<PESSIMISM>
IMHO, all this sudden talk about possible life on Enceladus is stretching the odds a bit too far. For all we know, liquid water (if it indeed exists in large quantities) could have persisted going back only a few tens of millions of years. Given the amount of time it took life to evolve on Earth, that kinda looks short, doesn't it?
Also, detection of fairly pure water as opposed to sulfuric acid on Europa doesn't IMHO go in favor of a suitable biosphere. Pure water just doesn't do it for life -- it's the organics and various other chemicals that do the trick. Granted, heavier organic species could still be detected lower in the plumes.
Enceladus is also a pretty small place, more likely to be in 'equilibrium' regarding energy or 'food' distribution so wouldn't that make any biologic metabolism hard to work?

All in all, to me Europa (even Titan's hypothetic subsurface ocean) is a far more likely candidate for life, even if it is much, much harder to explore. That said, Enceladus is still far more likely to harbor life now than Mars is -- at least here we have evidence of liquid instead of grasping at straws as on Mars.
</PESSIMISM>

[Guest_Richard Trigaux_*]

<PESSIMISM>
IMHO, all this sudden talk about possible life on Enceladus is stretching the odds a bit too far. For all we know, liquid water (if it indeed exists in large quantities) could have persisted going back only a few tens of millions of years. Given the amount of time it took life to evolve on Earth, that kinda looks short, doesn't it?
Also, detection of fairly pure water as opposed to sulfuric acid on Europa doesn't IMHO go in favor of a suitable biosphere. Pure water just doesn't do it for life -- it's the organics and various other chemicals that do the trick. Granted, heavier organic species could still be detected lower in the plumes.
Enceladus is also a pretty small place, more likely to be in 'equilibrium' regarding energy or 'food' distribution so wouldn't that make any biologic metabolism hard to work?

All in all, to me Europa (even Titan's hypothetic subsurface ocean) is a far more likely candidate for life, even if it is much, much harder to explore. That said, Enceladus is still far more likely to harbor life now than Mars is -- at least here we have evidence of liquid instead of grasping at straws as on Mars.
</PESSIMISM>

<OPTIMISM>
Yes, there is likely few energy source into Enceladus (perhaps some radiioactivity...) and for this reason I don't expect to find enceladians, and even not cells. But why not proto-cells. On Earth you can make them easily, in adding some phospholipids into water in a test tube: tiny vesicles form, the size of cells, which are thought to be the origin of true living cells membranes. Such vesicles can harbour catalysts, favouring the most efficient, and engage into a evolution process untill true cells appear. But I think you are right not to expect much further steps than vesicles containing self-catalists made on amino acids and nucleic acids, without even a DNA code. This would already be a fantastic finding.

On the composition of water, if Enceladus core contains much comet-like materials, so mandatorily it will contain all the pro-life chemistry. So we have all reasons to expect a biochemistry, and even the beginning of appearance of life. The question is how far it went, and what it will tell us about our own origins.
</OPTIMISM>


Note that The plumes could be produced by "hot" ice sublimation, not by actual flowing water. A water flow this size would quickly freeze, I think. If the Tiger stripes are actually convective patters in ice, we should expect to find "hot" ice everywhere. But infrared results show that heat is concentrated into narrow fissures. So I think that the process is similar to Earth oceans: water rises along faults, and freeze into them, keeping them wider and wider, until it crack again to let more water rise. That makes not sure that liquid water actually makes to the surface, but fresh ice does, eventually containing evidences of biochemistry or cells. But it is not sure that these evidences are really expelled with the plumes, so that Oberth's idea will not necessary work. Anyway it is worth trying, and many times cheaper than any other kind of mission we can imagine.

[jmknapp]

Would a ballute work in a water vapor plume at an altitude of 10 km?

Could be water vapor and ice particles though--kind of abrasive. If water vapor is coming out of the vents at high pressure and temperature (above 0C anyway) wouldn't it condense rapidly, effectively like a snow-making machine?

[Guest_Richard Trigaux_*]

Could be water vapor and ice particles though--kind of abrasive. If water vapor is coming out of the vents at high pressure and temperature (above 0C anyway) wouldn't it condense rapidly, effectively like a snow-making machine?

exactly

[Guest_BruceMoomaw_*]

This has certainly put the cat among the pigeons where planning for the next decade of planetary probes is concerned. It had pretty much been decided that Europa Orbiter was a higher priority for the next big outer Solar System mission than a Titan mission -- but now we're going to have to seriously consider possible designs for a mission that could further investigate both Titan and Enceladus, and whether such a mission would on the whole be higher-priority than Europa Orbiter.

[Bob Shaw]

Oh, dear. Jason might not be very pleased by all this use of the L-word, messing up his nice ice-worlds with that nasty self-replicating goo... ...it'd be a helluva thing if the Saturn system has been infected too!

Speaking of which, we are all familiar with the concept of the inner planets exchanging rocks from time to time - so what about the moons of the outer planets (etc)?

Bob Shaw

[Guest_paulanderson_*]

There is an interesting finding noted in Emily's latest blog entry on Enceladus (March 17), the discovery of acetylene in the plumes:

http://www.planetary.org/blog/article/00000498

As mentioned, the formation of acetylene normally requires the breakdown of long-chain hydrocarbons or temperatures of 1,770 Kelvin, according to Dennis Matson from the Cassini team. He thinks that catalytic chemistry may be responsible instead. How might that work? I could see such high temperatures being the most unlikely, but what about long-chain hydrocarbons, that were being broken down somehow? How plausible or significant might that be?

Interestingly, there are also apparently other "hot spots" in the south polar area, but separate from those in the tiger stripes.

[Guest_Richard Trigaux_*]

Acetylene? interesting.

This speaks in favour of some pre-life self-catalytic chemistry. Hopefully more. Bacteria could live without oxygen, just in transforming molecules (for instance the common sugar to alcohol transformation). On the other hand, acetylene is an energetic molecule (which needs energy to be created) so that it can hardly be the end result of a food chain, unlike methane.

Also good new that there are severa hot spots. In case what we see today would be not permanent, all the spots cannot stop all together.

[Guest_RGClark_*]

Oh, dear. Jason might not be very pleased by all this use of the L-word, messing up his nice ice-worlds with that nasty self-replicating goo... ...it'd be a helluva thing if the Saturn system has been infected too!

Speaking of which, we are all familiar with the concept of the inner planets exchanging rocks from time to time - so what about the moons of the outer planets (etc)?

Bob Shaw

This report suggests kilometer-scale impacts on Earth could send meteorites to the outer planets:

Earth rocks could have taken life to Titan
18:08 17 March 2006
NewScientist.com news service
Maggie McKee, Houston
http://www.newscientistspace.com/article/d...e-to-titan.html


- Bob Clark

[Guest_BruceMoomaw_*]

Yeah, we've got a discussion of that going in the Europa section ("Meteoroid transfer of Earth life to Europa?")

[Guest_paulanderson_*]

Acetylene? interesting.

This speaks in favour of some pre-life self-catalytic chemistry. Hopefully more. Bacteria could live without oxygen, just in transforming molecules (for instance the common sugar to alcohol transformation). On the other hand, acetylene is an energetic molecule (which needs energy to be created) so that it can hardly be the end result of a food chain, unlike methane.

Also good new that there are severa hot spots. In case what we see today would be not permanent, all the spots cannot stop all together.

Some additional info on acetylene, courtesy bonzelite on the Space.com forum:

Precursor to Proteins and DNA Found in Stellar Disk
http://www.keckobservatory.org/news/scienc...s46/051220.html

"The two organic compounds found -- acetylene and hydrogen cyanide -- are commonly found in our own solar system, such as the atmospheres of the giant gas planets, the icy surfaces of comets, and the atmosphere of Saturn’s largest moon, Titan. Another carbon-containing species detected, carbon dioxide, is widespread in the atmospheres of Venus, the Earth, and Mars.

"If you add hydrogen cyanide, acetylene and water together in a test tube, and give them an appropriate surface on which to be concentrated and react, you'll get a slew of organic compounds including amino acids and a DNA purine base called adenine," said Keck Astronomer Dr. Geoffrey Blake, of the California Institute of Technology in Pasadena and co-author of the paper. “Now, we can detect these same molecules in the planet zone of a star hundreds of light-years away..."

While the precise events leading up to self-replicating nucleic acids remains unclear, the molecules of acetylene (C2H2) and hydrogen cyanide (HCN) have been shown to produce the base compounds necessary to build RNA and DNA."

[Guest_Richard Trigaux_*]

As I said, acetylene is an energized molecule, which needs energy to be produced, and releases this energy when destroyed (in more of the energy it produces when it reacts with oxygen).

This is a serious hint as what there is an active chemistry into Enceladus, with an energy source, and thus a good possibility for a proto-life chemistry, or more.

If we are really sure that this acetylene is born from the ground, and not from further reaction of methane with UV light. But it seems little probable that UV light could polymerise two methane molecules in only some minutes.

[edstrick]

"If we are really sure that this acetylene is born from the ground, and not from further reaction of methane with UV light. But it seems little probable that UV light could polymerise two methane molecules in only some minutes."

Amen.

That bogglaceous discovery goes with (as I understand) the a most interesting anti-discovery: the continuing lack of any emitted ammonia.... as easy as it is to photolyse ammonia compared with water, it seems implausible it would have been ALL gone by the time the emitted materials got to where they were measured.

[The Messenger]

"If we are really sure that this acetylene is born from the ground, and not from further reaction of methane with UV light. But it seems little probable that UV light could polymerise two methane molecules in only some minutes."

Amen.

That bogglaceous discovery goes with (as I understand) the a most interesting anti-discovery: the continuing lack of any emitted ammonia.... as easy as it is to photolyse ammonia compared with water, it seems implausible it would have been ALL gone by the time the emitted materials got to where they were measured.

I wouldn't expect life without ammonia...but then I wouldn't expect life, period. All the stretch marks on Enceladus would seem to me to indicate a source of abundent internal energy - enough to produce acetylene without catalysis.

[Guest_BruceMoomaw_*]

"If we are really sure that this acetylene is born from the ground, and not from further reaction of methane with UV light. But it seems little probable that UV light could polymerise two methane molecules in only some minutes."

Amen.

That bogglaceous discovery goes with (as I understand) the a most interesting anti-discovery: the continuing lack of any emitted ammonia.... as easy as it is to photolyse ammonia compared with water, it seems implausible it would have been ALL gone by the time the emitted materials got to where they were measured.

I mentioned earlier, in the "Great Ammonia Mystery" thread, that I asked about precisely that possibility at the Europa meeting -- and was told that the gas analyzed by Cassini had been emitted by the surface vents only about 15 minutes earlier, which is simply too short a time for solar UV at Saturn's distance to destroy most of any ammonia in the gas. So it really IS missing (or, at least, very scarce) in the original vapor. As for acetylene: since it takes much longer for UV to break down CH4 than NH3, I imagine it would also take a lot longer for UV to turn CH4 into C2H2.

[Guest_paulanderson_*]

Does anyone have further info about the composition of the dark green organic material seen streaked on the icy surface, as mentioned in the "Tiger, Tiger Burning Bright" article? Would this have come from the plumes presumably?

[ljk4-1]

Science/Astronomy:

* Encore For Enceladus! Saturn Moon Ripe For Astrobiology Exploration

http://www.space.com/scienceastronomy/0604...ery_monday.html

The discovery of apparent liquid water reservoirs erupting in Yellowstone-like
geysers on Saturn's moon Enceladus has produced a gusher of questions.


* Commentary: Astrobiology Research Threatened at NASA

http://www.space.com/searchforlife/060330_seti_thursday.html

I sympathize with Griffin, but do not agree with the way the choices are being
implemented.

[volcanopele]

Does anyone have further info about the composition of the dark green organic material seen streaked on the icy surface, as mentioned in the "Tiger, Tiger Burning Bright" article? Would this have come from the plumes presumably?

I think the author misinterpreted the results from ISS and VIMS. The greenish color of the tiger stripes doesn't come from the simple organics VIMS found, but from the coarse-grained, crystalline water ice found there. We are still working on whether the greenish color comes from plume deposits, thermally altered water ice, or magmatically-emplaced ice.

[The Messenger]

Science/Astronomy:

* Encore For Enceladus! Saturn Moon Ripe For Astrobiology Exploration

http://www.space.com/scienceastronomy/0604...ery_monday.html

In short, Porco said, "Cassini is so very well equipped, that it could be the precursor mission for a future landed mission to the south pole of Enceladus. In other words, we could do in the next few years with Cassini at Enceladus what the next orbiter of Jupiter would do at Europa."

It sounds like they - Carolyn, is/are so worried about extended mission funding, they are arguing the Cassini/extended should be funded, if necessary, at the the expense of the Europa mission

[ugordan]

The greenish color of the tiger stripes

So which is it in the end -- greenish or bluish???

It sounds like they - Carolyn, is/are so worried about extended mission funding, they are arguing the Cassini/extended should be funded, if necessary, at the the expense of the Europa mission

While it seems she is concerned about EM funding, I don't think she's proposing stealing from an Europa mission. She does have a point that Cassini has it easier when trying to find a place to land on Enceladus for a future mission. The tiger stripes are narrow and all they need to know is the locations of more powerful vents.
A Europa orbiter would undoubtedly have a much more difficult task of finding where the ice is thinnest.

[volcanopele]

So which is it in the end -- greenish or bluish???

Well, it's more blue-green really. Kinda minty

There are even a range of ridges in the trailing hemisphere I've been calling the "Minty Mountains". Sorry, I know, bad joke

Seriously, the spectrum is rather flat between our UV3 filter and our GRN filter (check out the supplementary materials section of our Science paper). If anything, the stripes are slightly brighter in the green filter, making it more green than blue, thus mint green.

I should point out that in true color, there isn't much color to speak of. the tiger stripes appear darker than the surrounding terrain, but they aren't really all that different in color.

While it seems she is concerned about EM funding, I don't think she's proposing stealing from an Europa mission. She does have a point that Cassini has it easier when trying to find a place to land on Enceladus for a future mission. The tiger stripes are narrow and all they need to know is the locations of more powerful vents.
A Europa orbiter would undoubtedly have a much more difficult task of finding where the ice is thinnest.

I think there is some concern about funding for an extending mission, such that we shouldn't assume that it will happen, but rather we should fight for and justify. However, I don't think funding such an extended mission requires it be an either/or with a Europa mission. A seperate Titan mission (and/or Enceladus) and Europa maybe...

I think our task does have a lot to do with identifying the locations of the vents and to see if they vary over time. Do the vents jump around along the fractures? Do some fractures shut down (venting) while others start up?

[dvandorn]

Here's an offbeat question:

Are the Enceladan plumes dense enough that they would provide any amount of braking to an Enceladus lander?

I can imagine a lander that spends a good amount of its descent trajectory using the friction of the plumes for deceleration. But this assumes that they provide enough density for a noticeable amount of braking.

-the other Doug

[ElkGroveDan]

Are the Enceladan plumes dense enough that they would provide any amount of braking to an Enceladus lander?

But then they'd have to install de-icing equipment.

[ugordan]

Are the Enceladan plumes dense enough that they would provide any amount of braking to an Enceladus lander?

I don't think the plumes are dense at all. They can only be visible in very high phase angle images and probably would be very hard to notice even if you were standing right there beside one of those vents. If they were dense enough for aerobraking, they'd probably have been detected ages ago.

[Guest_paulanderson_*]

I think the author misinterpreted the results from ISS and VIMS. The greenish color of the tiger stripes doesn't come from the simple organics VIMS found, but from the coarse-grained, crystalline water ice found there. We are still working on whether the greenish color comes from plume deposits, thermally altered water ice, or magmatically-emplaced ice.

Ok, I was thinking that these were other dark streaks separate from the tiger stripes, but then I saw that later in the fourth paragraph she makes another reference to the tiger stripes as containing the dark organic material; missed that point before. So this is actually just the blue-green water ices already discussed? Still very interesting though, of course.

Btw, I miss your Titan Today blog, I used to check it regularly when it was still active, an excellent Titanian resource. But I'll check the new revamped one now also you've just started, good luck with it.

[volcanopele]

Science/Astronomy:

* Encore For Enceladus! Saturn Moon Ripe For Astrobiology Exploration

http://www.space.com/scienceastronomy/0604...ery_monday.html

The discovery of apparent liquid water reservoirs erupting in Yellowstone-like
geysers on Saturn's moon Enceladus has produced a gusher of questions.

An interesting article, though they still quote the wrong distance to Enceladus for EN61. That's what I expected they would officially announce.
A few additional comments:

""One could even imagine an extended mission with enough emphasis on Titan and Enceladus," he said, "to constitute a kind of 'Cassini Astrobiology Mission'"."

I swear if the extended mission is called that...I may just start doing Mars stuff... Right after Carolyn just said in the article that Cassini is not instrumented to look for microbes, at least call the mission for what it is rather than using Congress-friendly buzz words to make the sale.

"Of course, how close Cassini can get to this action from Enceladus will be ultimately determined by spacecraft safety issues ... "but that would be the goal," she said."

I'll admit, on Saturday, I was considering posting an april fool's joke here about how one of the extended missions plans that was in the "lead" in terms of being chosen, was an end of mission plan where Cassini would make progressively closer passes over the south pole, including oen that brought it within 2 km of the surface.

[Guest_paulanderson_*]

I think the author misinterpreted the results from ISS and VIMS. The greenish color of the tiger stripes doesn't come from the simple organics VIMS found, but from the coarse-grained, crystalline water ice found there. We are still working on whether the greenish color comes from plume deposits, thermally altered water ice, or magmatically-emplaced ice.

I noticed that one of the papers linked to from the article, the abstract for it, mentions "light organics" found on the surface. Now I'm not sure again; are the "dark green streaks of organic material" in the article referring only to the tiger stripes or are there other streaks also? I had only heard of the tiger stripes though, with the bluish colouring from the ice deposits. Are the simple organics on the surface, in the plumes or both? I had thought they were in the plumes. Somebody in another forum is adamant that the dark green organic streaks, as described in the article, are there, and that you are completely wrong (I had mentioned your clarification, that the article was mistaken, but he isn't buying it)...

[volcanopele]

I noticed that one of the papers linked to from the article, the abstract for it, mentions "light organics" found on the surface. Now I'm not sure again; are the "dark green streaks of organic material" in the article referring only to the tiger stripes or are there other streaks also?

The simple organics seen by VIMS are found only within the tiger stripes in Enceladus' south polar region, and at no other location. This identification is based on two small absorption bands at 3.44 and 3.52 microns, attributed to short-chain organics. Again, the blue-green color of the tiger stripes is due to coarse-grained water ice, NOT these short-chain organics. The author of the special section intro did not interpret our results correctly.

I should point out that Cassini ISS and VIMS have found other examples of blue-green material on the surface, identified as coarse-grained ice. VIMS found NO evidence for the 3.44 and 3.52 micron absorption bands at these locations. Images of these blue-green areas indicate that these areas correspond with outcrops along canyon and fracture walls as well as at the tops of ridges, likely areas where the downslope movement of Enceladus' fine-grained regolith has exposed the coarser-grained bed ice.

I had only heard of the tiger stripes though, with the bluish colouring from the ice deposits. Are the simple organics on the surface, in the plumes or both? I had thought they were in the plumes.

Both. The INMS instrument found CH4 in the plume as Cassini flew through it in July. Methane made up about 1.6% of the gases in the plume at the time of the measurements. And again, VIMS found short-chained organics within the tiger stripes.

Somebody in another forum is adamant that the dark green organic streaks, as described in the article, are there, and that you are completely wrong (I had mentioned your clarification, that the article was mistaken, but he isn't buying it)...

I don't know what else I can say other that to urge that reader to check out the VIMS paper in the Science special issue if at all possible.

[Rob Pinnegar]

If they were dense enough for aerobraking, they'd probably have been detected ages ago.

Also, if they were dense enough for aerobraking, it'd be hard to explain how Enceladus could lose that much mass per second over long periods of time without evaporating completely.

[Guest_BruceMoomaw_*]

I'm just waiting for a chance to get all the way to a city library where I can read both Waite's article on the mass spectral results, and Brown's paper on the VIMS results -- neither of which I've seen yet. But the abstract for Waite does confirm that the mass spectrometer also found what are probably traces (<1% each) of acetylene and propane in the plume.

[Guest_Myran_*]

This is odd, and perhaps unrelated.
But Saturns outermost ring which is thought to be created by Enceladus are blue. The newly outermost ring of Uranus have also been found to be blue, and here at Space.com its stated that the blue Uranus ring appear to be associated with the tiny moon Mab.
Its thought that Mab provides the ring from dust released by meteoroid impacts.
But what if, it turns out also the moon Mab got geysers? The case for a non liquid cause would get stronger, too bad theres no Uranus orbiter in the pipeline so we could settle the question.

[volcanopele]

But what if, it turns out also the moon Mab got geysers? The case for a non liquid cause would get stronger, too bad theres no Uranus orbiter in the pipeline so we could settle the question.

The color is related to the size and composition of the particles, not necessarily how they are formed.

And if Mab (D ~ 25 km) had geysers, I think we should just throw up our hands and call it a day

[Guest_Myran_*]

volcanopele wrote: The color is related to the size and composition of the particles, not necessarily how they are formed.

And if Mab (D ~ 25 km) had geysers, I think we should just throw up our hands and call it a day

You are absolutely right about colour caused by the size, and that was in fact that started this line of wild speculation of mine since meteroid collisions would create fragments in a variety of sizes.

Yet I did phraze it tentatively since it appear remote also to me, while I did have Chiron in mind when writing the former post remembering that Chiron manage to have quite some outgassing and possibly geysers, and Chiron in its orbit between Saturn and Uranus should recieve as little sunlight as Mab.

In all fairness, it must be pointed out that also this comparision isnt entirely fair. Since Chiron might not have been in its present orbit for a very long time astronomically speaking, and it in fact might be the innermost KBO where the outbursts of gas and dust are signs that Chiron suffers from a heatstroke in its new hot environment.

[Guest_BruceMoomaw_*]

VERY interesting interview with the Enceladus researchers at the EGU meeting:
http://news.bbc.co.uk/1/hi/sci/tech/4895358.stm . There's lots of entirely new information in this article.

[Bob Shaw]

Interesting graphic, too. The article went a little awry describing water volcanoes on Earth, though...

Bob Shaw

Attached thumbnail(s)

 

[centsworth_II]

Wouldn't the water pocket sit directly on the hot rock? How could there be ice between the water and hot rock?

[The Messenger]

Wouldn't the water pocket sit directly on the hot rock? How could there be ice between the water and hot rock?

Focused Lasers, if they have the technology, focused sound waves or radar, if they don't

[helvick]

How could there be ice between the water and hot rock?

Pressure. Lots of it.

[centsworth_II]

Focused Lasers, if they have the technology, focused sound waves or radar, if they don't

Hey, I've read about natural nuclear reactors existing in Africa millions of years ago, so who knows?

Pressure. Lots of it.

So the ice between the water pocket and rock is actually warmer than the water, but pressure is keeping it solid? That makes sense to me. Of course no one knows the real situation, but if that's a possibility...

[Guest_Richard Trigaux_*]

Pressure. Lots of it.

High pressure ice can be hot, and even very hot, like rock. But such ice cannot exist on Enceladus, there is simply not enough pressure. I have estimated once, for a SF book, that on a planet twice the Earth, with a very deep ocean, high pressure ice was starting at 160kms deep. (and it don't float on water). On Enceladus, the ice is about 120kms deep, and the gravity is much lower...

so the sketch above must not be interested literally. Ordinary ice tends to melt with pressure, so we may expect a thin layer of liquid water in contact with the rock, and all ice above. Then the heat propagates into the ice through convective movements. Basically near zero ice is soft enough to behave that way, and it becomes hard only near the surface, where the movement breaks it inco scales of hard cold ice. Into the cracks, hotter ice sublimates.

Into ice, water cannot rise higher than 90% of the ice depth. Thus to have a geyser of liquid water requires a further process, like a gas driving the eruption. And a powerful enough eruption not to freeze into the vent.

[The Messenger]

Hey, I've read about natural nuclear reactors existing in Africa millions of years ago, so who knows?
So the ice between the water pocket and rock is actually warmer than the water, but pressure is keeping it solid? That makes sense to me. Of course no one knows the real situation, but if that's a possibility...

No, because pressure causes freezing point elevation, not depression. It is difficult to see how a geyser could form from direct sublimation of water-ice. It takes to many calories to transition both phases, and still have enough gas pressure to direct the molecules upward.

I think a better answer is that there are pockets of water under the ice, or in a rock matrix. This water would immediately erupted into the gaseous phase if and when exposed to Enceladus surface pressure, and as these jets emerge, it also seems likely that the amount of heat energy removed would quickly freeze the water in a very dynamic, cyclic process of eruptions...unless the heat source is extremely hot.

This one is going to take some time, and more data, to sort out.

[Guest_Richard Trigaux_*]

No, because pressure causes freezing point elevation, not depression.

False: until about 1600 bars, the freezing point of pure water decreases about 1°C for every 100 bars. Only after high pressure ice have a freezing point raising with pressure, as for most bodies. But I think such pressure cannot be reached on Enceladus.

[ljk4-1]

Has anyone determined why the geysers are happening only
in one area of Enceladus that we can tell so far?

[Guest_Richard Trigaux_*]

The most likely explanation is about convection patterns. For ideal fluids into simple shaped recipients, convection organizes itself in "Benard cells". Each cell has a rising current and a lowering current. The number of Benard cells depend on a thermodynamic number, the Reynold number. In gross a low Reynolds number gives simple convection patterns, for instance one benard cell. With increasing Reynolds number (increasing energy, to simplify) the number of cells increases, until the convection becomes chaotic. What is interesting is that mathematic models were made of ideal planet mantle convection. Earth was found chaotic, from an intense heat transfer. But smaller planets were found having only few convection cells, for instance two at the poles and four at the equator. Enceladus would be at the lower edge, with only one cell. Of course in real fluids there are other causes or irregularities, which may alter the basic pattern, or cause the cells to rise in an unexpected place. But basically, from thermodynamics, Enceladus could not have several cells, and the unique cell has to rise somewhere anyway.

[The Messenger]

False: until about 1600 bars, the freezing point of pure water decreases about 1°C for every 100 bars. Only after high pressure ice have a freezing point raising with pressure, as for most bodies. But I think such pressure cannot be reached on Enceladus.

So for water ice under the conditions expected at Enceladus, what is the heat of sublimation?

[Guest_Richard Trigaux_*]

So for water ice under the conditions expected at Enceladus, what is the heat of sublimation?

Sorry, I don't know this. Google it: water ice enthalpy.

At rough guess, only relatively hot ice can sublimate. -50°C, -100°C? It is still hotter than what was measured. But the measures were doing an averaging on distance of several kilometres. So there may be much hotter point, up to zero.

Anyway to maintain the sublimation rate observed, we need a constant renewing of ice. Or the ice has a karst form, with cavities where the sublimation takes place. That is: sublimation would quickly stop on parts of ice directly exposed to space. But it would continue in underground cavities, which will become larger and larger. So a realy difficult place for a lander, with hidden holes, tracherous ground, sharp spikes, etc. But once into such a cavity, it is really the best place to search for microbes, or whatever there is.


Some here prefer to speak of water flowing rather than ice sublimating. This would better expect the quick variations of the plumes. But sublimation could give variations too, for instance when a cavity roof is crumbling down.


You need the heat of sublimation, but for any calculus we first need the mass of gasses produced.

[Bob Shaw]

Surely there are well-observed examples of water-ice sublimation from subsurface reservoirs producing plumes?

I think they're called 'comets'.

Bob Shaw

[Guest_Richard Trigaux_*]

Surely there are well-observed examples of water-ice sublimation from subsurface reservoirs producing plumes?

I think they're called 'comets'.

Bob Shaw

Indeed I don't see any difference between comet plumes and Enceladus plumes.

Anyway in vacuum any plume takes the same shape.

The Cassini scientists insist as what the plumes would be sharp because they would be forced out of vents. But in vacuum, whatever it is a rocket exhaust or snow sublimating, the plume is alway about the same shape.

[climber]

Indeed I don't see any difference between comet plumes and Enceladus plumes.

Anyway in vacuum any plume takes the same shape.

The Cassini scientists insist as what the plumes would be sharp because they would be forced out of vents. But in vacuum, whatever it is a rocket exhaust or snow sublimating, the plume is alway about the same shape.

Is that also true on Triton ? Io ?

[Bob Shaw]

Is that also true on Triton ? Io ?

No. Triton's plumes went straight up in the thin atmosphere, and then sheared in high altitude winds. Some of Io's plumes might be hot enough to glow in visible light, so they could look rather different to the rocket exhaust style of outflow. And after that, they're made of quasi-volcanic materials rather than ices, so may well follow more discrete parabolic paths with less diffusion.

Bob Shaw