[X] My Assistant

[Guest_Richard Trigaux_*]

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

The idea is as follows: send a stardust-like mission to capture particules from the Enceladus plume.

I think it is the cheapest way to have infos on what is going on into Enceladus, if it has a biochemistry and how far it evolved.

I allow myself to better the idea: the probe could have three targets.


1) when passing near Saturn, catches ring particules
2) Using Titan as a gravitationnal aid, captures smog particules (fortunately they reach very high)
3) passes into Enceladus plume, captures eventual evidences of biochemistry in Enceladus.

And back to Earth! It even don't need to actually satellise around Saturn, if it is well aimed. The only difficulty is a precise navigation, to aim into a 10x10kms window into the plumes, and a bit of fuel.

The only serious problem is not to bring back some alien bacteria on Earth! Eventually the aerogel containing the Enceladus particules would be coated in something after use, so that there would be no possible contamination, in any way.

Even if the mission fails, a low pass over the Tiger Stripes would allow to obtain precise images of the vents (or more likely zones where the ice is sublimating, like in a comet), provided we have a special shutter compensating for motion blur. Such images would be anyway a necessary preliminary step before sending a lander on Enceladus, and even before designing it (depending on the geometry of the vents, which may be complicated or hazardoous).

[helvick]

1) when passing near Saturn, catches ring particules
2) Using Titan as a gravitationnal aid, captures smog particules (fortunately they reach very high)
3) passes into Enceladus plume, captures eventual evidences of biochemistry in Enceladus.

Can any of the rocket scientists out there comment on the likelihood of managing to do some (or all) of the above in a single pass that has the sampler rapidly returning to earth?

[scalbers]

Even if the mission fails, a low pass over the Tiger Stripes would allow to obtain precise images of the vents (or more likely zones where the ice is sublimating, like in a comet), provided we have a special shutter compensating for motion blur. Such images would be anyway a necessary preliminary step before sending a lander on Enceladus, and even before designing it (depending on the geometry of the vents, which may be complicated or hazardoous).

One constraint on the tiger stripe imaging is the approaching end of the southern Enceladean summer. The south polar regions will be mostly in shadow for quite a while, until we approach the next summer solstice around 2030.

[Guest_BruceMoomaw_*]

Drat. We would still, however, be able to use a thermal imager on the craft to map the precise location of the warm vents with great accuracy on a low-altitude flyby.

As for combining an Enceladus sampler with sampling flybys of Titan or the rings (or, as James Oberg suggests, Io during the craft's Jupiter gravity-assist): it's tempting, but DON'T OVERDO IT. Any of this -- except maybe the ring sampling -- would dangerously overcomplicate the mission.

[helvick]

One constraint on the tiger stripe imaging is the approaching end of the southern Enceladean summer. The south polar regions will be mostly in shadow for quite a while, until we approach the next summer solstice around 2030.

So that would be an imaging constraint but should not be a constraint on a sample return, right?

[scalbers]

Right, this is just a sunlight imaging constraint, though the spring equinox would be about 2025. There might be some seasonal constraints on the trajectories though I suspect it wouldn't be too much of an issue.

In visible light, there's always starlight if we can sit long enough over one place to collect those photons.

[David]

Well -- surely the most likely scenario is that there is no biochemistry going on in Enceladus, and so the probe would be coming back with what? It's a long way to go for a teaspoon of water. Such a probe ought to be prepared to get some science return even if the plume chemistry is uninteresting.

[Guest_BruceMoomaw_*]

Which is precisely why we need to know as much as Cassini can possibly tell us about the composition of the plumes. But they definitely are not just plain water -- the plume is about 3-4% each nitrogen and CO2, 1.5% methane, and probably smaller amounts of other organics (acetylene and propane are thought to have been detected) and other substance. We simply don't know how far organosynthesis may have gone in this environment.

It is certainly important, however, NOT to jump to the conclusion that there's a good chance Enceladus is a Fountain of Life, even if this wet and organic environment has existed for hundreds of millions of years. As Chris Chyba has pointed out, the carbonaceous-chondrite asteroids are very rich in both water and fairly complex organics (including amino acids) -- and during the Solar System's early days, they also contained enough Al-26 (known to have been scattered throughout the forming Solar System by a coincidental nearby supernova blast) to warm their interiors to the point that a lot of that water was liquid for tens or even a few hundred million years. But not one carbonaceous meteorite shows the slightest sign that biosynthesis went very far -- which, as Chyba says, is actually the strongest evidence we have that the appearance of life really MAY require a major stroke of chance luck even under favorable conditions, and that life may therefore be rare in the Universe.

In any case, I repeat that it's risky to try to make such a mission do too much else. Flying it by Titan or Io would require some additional clever (and risky) interplanetary billiards. Having it brush through the region outside Saturn's visible rings to collect ring particles might be more practical as a bonus. And I suppose it could not only make more IR observations of Enceladus during the sampling flyby, but perhaps carry ice-penetrating radar to try to get a better idea of just what is going on down there. (Edwin Kite and I have suggested this in the past for the Europa Ice Clipper, to test whether Janusz Eluszewicz is right in his fears that ice-penetrating radar on Europa Orbiter might not be able to punch deeply through it at all. But Bob Pappalardo and others have recently provided evidence that Eluszewicz's fears are unfounded -- and if we're going to send Europa Orbiter there anyway with a large payload of other instruments, it won't cost much to add the radar sounder to it in any case. Besides, even if the radar can't penetrate deeply at some locations on Europa, it may well be able to do so at other places.)

Sushil Atreya and the other scientists most interested in outer-planet entry probes have recently firmly reached the conclusion (which they announced at the November COMPLEX meeting) that you don't really need very deep entry probes (which are hard to design) for the first probes to Saturn, Uranus or Neptune -- although at some point later on they will have their uses, as they will for Jupiter. Instead, they recommend that the next mission after Juno that is specifically directed to study ANY of the giant planets should be a relatively simply New Frontiers mission to fly by Saturn and drop off only two (or maybe just one) comparatively lightweight and cheap Galileo-type vented entry probes to analyze the atmosphere down to about 20 bars, while the flyby craft uses a microwave spectrometer similar to Juno's to measure the water and ammonia levels at much great depths (with the entry probe also providing crucial calibration data for that, such as the Galileo probe has already provided for Juno). If we decide to defer Neptune Orbiter and instead return to Uranus and/or Neptune first with more flyby missions, the same thing could be done there -- although the main craft would carry more instruments to study the planet and its moons. But, again, I think that combining such a Saturn entry probe with an Enceladus sampler presents serious and probably insuperable trajectory problems.

[Guest_Richard Trigaux_*]

Thanks all for your interesting contributions.

helvick, I though again to the right trajectory this night. The best trajectory would be an hyperbolic trajectory into the Saturn system, which would result in a gravity assist sending back the probe to Earth. Centered into the Saturn referencial, the departing branch would be toward the Sun, at right the moment where Enceladus is on the way. As an important constrain of the mission is SEEING the plumes in order to aim on them, and this can be done only in looking at Enceladus from its dark side (unless the camera has some coronograph). At this moment the probe has to navigate autonomously and accurately correct its trajectory in order to aim at the plumes.

Catching particules of the ring is easy, and even mandatory, as the ringplane has to be crossed at a moment or another. Just the right place must be choosen, not to just catch the Enceladus products. But, as Bruce noted, also catching Titan haze may fairly complicate the mission: -pose serious constrains on the timing -need other corrections, as the probe will somewhat aerobrake, in an unknown amount -the science bonus is questionnable. Just see if it is possible. Perhaps it will be easy, if Titan happens to be on the departing trajectory too.

The overal idea is to make a relatively cheap mission. At least it would be cheaper than a flagship mission like Cassini or Juno, and so it would not impede the funding of Juno or another Europa project.

In order to be cheap, the ship must be as small as possible, knowing that the cost and the mass of fuel are multiples of the mass of a ship. For this reason the ship would have no large gain antenna. Only a small dish to slowly return the (large) amount of close Enceladus images. (Galileo told us that it is possible... ) So it would entirely rely on software and mass data storage.

The ship must have a camera, otherwise it could not navigate into the Saturn system. It must have a complex software, not just executing a program, but able to understand the situation and correct for any unexpected event. Software has no weight, and it can save many fuel weight and structural wheight.

A difficult moment would be the close imaging of the vents without motion blur, in an encounter of only some seconds. The camera has no time to change filters, so only one filter must be used (centered on likely organic compouds) or several cameras with different filters. Shutter must be very speedy, and several overlapping images of the same area must be taken, allowing for a super-resolution reconstruction.

As scalbers noted, there is a serious constrain about the tiger stripes going into winter darkness. I think we have still the time to catch them, but the design of the probe must be started at once. After, it will be more difficult, perhaps even the plumes will be extinct, it they need the sun heat. (Likely there would be no liquid water gushing, but just hotter ice, which would sublimate only when heated by the sun, like in a comet).

The main interest of Oberg's idea is that is seems the simplest and cheapest way to get a soon answer about a possible life in another place, even simplest than with Europa which will require at least a lander.



Bruce, about your reflexions on the appearance of life, I would say that the very first step, the 100% chemical step, seems rather common. But that don't imply that the following steps are as much common. These steps require stable conditions and liquid water, conditions which were likely never fulfilled in comets and asteroids, even with a heating by Al26, as these bodies are very small. On Enceladus, there is likely liquid water since millions of years, with a chemistry similar to that of comets (and no massive ammonia or sulphuric acid poisoning) so that it is likely that some evolution could take place. At what rate? That depends on the conditions, if for instance the water inside Enceladus is at -10°C (min allowed for relatively pure liquid water like in the plumes) then evolution of life may be very slow or absent. But some bit of evoulution could have taken place, with the creation of proto-cells or something. In what extent? Which stage it reached? Only finding in ple plume a bio-catalist made of amino acids and nucleic acids would confort the known models on appearance of life. On Earth we have no record of these steps in the appearance of life. So Enceladus may provide us with an unvaluable insight on our origins, even if we don't find a single bacteria or DNA chain. Finding bacteria would of course be an incredible philosophy result, but finding an intermediary step would learn us more about how life appeared.

[Guest_RGClark_*]

...
It is certainly important, however, NOT to jump to the conclusion that there's a good chance Enceladus is a Fountain of Life, even if this wet and organic environment has existed for hundreds of millions of years. As Chris Chyba has pointed out, the carbonaceous-chondrite asteroids are very rich in both water and fairly complex organics (including amino acids) -- and during the Solar System's early days, they also contained enough Al-26 (known to have been scattered throughout the forming Solar System by a coincidental nearby supernova blast) to warm their interiors to the point that a lot of that water was liquid for tens or even a few hundred million years. But not one carbonaceous meteorite shows the slightest sign that biosynthesis went very far -- which, as Chyba says, is actually the strongest evidence we have that the appearance of life really MAY require a major stroke of chance luck even under favorable conditions, and that life may therefore be rare in the Universe.
....

The problem is that both DNA and proteins breakdown quickly when outside of an organism continually producing them. There have been claims of fossilized bacteria in some carbonaceous meteorites.
Most of the water that is detected in meteorites is in chemically bound form, not free liquid water. However, surprisingly there have been found small liquid water containing inclusions in some meteorites:

Asteroidal Water Within Fluid Inclusion-Bearing Halite in an H5 Chondrite, Monahans (1998).
Michael E. Zolensky, Robert J. Bodnar, Everett K. Gibson Jr., Laurence E. Nyquist, Young Reese, Chi-Yu Shih, Henry Wiesmann
Science 27 August 1999, Vol. 285. no. 5432, pp. 1377 - 1379
http://www.sciencemag.org/cgi/content/full/285/5432/1377

A LPSC report also discussed observing fluid inclusions in Martian meteorites:

Bodnar R.J.
Fluid Inclusions in ALH 84001 and Other Martian Meteorites: Evidence for Volatiles on Mars.
http://www.lpi.usra.edu/meetings/LPSC99/pdf/1222.pdf

They were described as containing mostly CO2, but it's possible they contain some portion of H2O.

As far as I know the micron-sized inclusions in meteorites have not been searched for microbes.
However, a recent report discusses a method that may work for such small inclusions:

Evaluation of the LIVE/DEAD BacLight Kit for Detection of Extremophilic Archaea and Visualization of Microorganisms in Environmental Hypersaline Samples .
Applied and Environmental Microbiology, November 2004, p. 6884-6886, Vol. 70, No. 11
http://aem.asm.org/cgi/content/full/70/11/6884



Bob Clark

[Guest_Richard Trigaux_*]

The problem is that both DNA and proteins breakdown quickly when outside of an organism continually producing them. There have been claims of fossilized bacteria in some carbonaceous meteorites.
Most of the water that is detected in meteorites is in chemically bound form, not free liquid water. However, surprisingly there have been found small liquid water containing inclusions in some meteorites:
...

It was said long ago that celle-sized carbon spherules found in the Orgueil meteorite (carbonacous chondrite fell in France in late 19th century) could be bacteria. I don't believe this too much, and seemingly this prospect was abandoned. But those things could be some preleminary steps into the appearance of bacteria. But the life appearance process would have stop when conditions became too cold.

[Guest_RGClark_*]

Perhaps we could collect some of the 1.6% methane in the plumes to use as propellant. But you would need oxidizer. There is no oxygen in the plumes.
There is *very* tenuous molecular oxygen around Saturn rings. My guess is this would not be enough.
Is there a low energy method to get an oxidizer out of the water, nitrogen, and carbon monoxide in the plumes? (Separating oxygen out of H2O is energy intensive.)


Bob Clark

[Guest_BruceMoomaw_*]

There ain't even any significant amount of carbon monoxide in them, according to Cassini's UV spectrometer (which, unlike its mass spectrometer, can distinguish between CO and N2). There IS a few percent of carbon DIOXIDE -- but we're talking about extremely small, ghostly traces of total plume vapor anyway: not enough to extract any conceivably useful amount of propellant from in any case.

[nprev]

So that would be an imaging constraint but should not be a constraint on a sample return, right?

One crucial payload element should be a hi-res IR imager, regardless. A dark south pole might even be advantageous in this respect; hotspot localization would be greatly facilitated by removal of the ambient noise from sunlight.

[Guest_BruceMoomaw_*]

One crucial payload element should be a hi-res IR imager, regardless. A dark south pole might even be advantageous in this respect; hotspot localization would be greatly facilitated by removal of the ambient noise from sunlight.

Also, let's not forget that while Enceladus' south polar region would be shielded from direct sunlight, it would NOT be shielded from Saturnshine -- and we already know from Cassini that you can get some quite useful visible-light photos out of that.