[X] My Assistant

[Holder of the Tw...]

The mission description PDF is now online.

Enceladus 3 Flyby

[CosmicRocker]

Can one of you astrobiololgy or icy body chemical types comment? I read the headlines noting the discovery of "complex organics," but the published spectrograph displays the heaviest broad peak centering around 40 Daltons. I wouldn't normally describe molecules of this weight range as "complex."

Are molecules heavier than the C2/CN/CO range typically considered complex by space scientists?

I noted that Emily's blog entry stated that "At higher masses, not shown on the graph above, "we saw more complex compounds, like propyne, propane, maybe even acetonitrile, and then we saw things even more complex. But they were so weak in signal that we didn't venture an identification." Propane and propyne should have appeared on that graph, since its X-axis goes up to 50 Daltons. Was that data simply erased from the publically released spectrograph?

[elakdawalla]

Can one of you astrobiololgy or icy body chemical types comment? I read the headlines noting the discovery of "complex organics," but the published spectrograph displays the heaviest broad peak centering around 40 Daltons. I wouldn't normally describe molecules of this weight range as "complex."

Are molecules heavier than the C2/CN/CO range typically considered complex by space scientists?

I noted that Emily's blog entry stated that "At higher masses, not shown on the graph above, "we saw more complex compounds, like propyne, propane, maybe even acetonitrile, and then we saw things even more complex. But they were so weak in signal that we didn't venture an identification." Propane and propyne should have appeared on that graph, since its X-axis goes up to 50 Daltons. Was that data simply erased from the publically released spectrograph?

I get the idea that any time you have more than one carbon in a molecule, space scientists call it "a complex organic molecule."

That language about higher masses was a bit of sloppiness on my part. The quote is correct but obviously some of the compounds he mentioned would have shown up on the graph; I should have split the quote a bit differently to make that clearer (just didn't have time yesterday). I don't believe the graph was altered in any way; I assume you don't see propane and propyne specifically called out on it because the abundances would be so small as to be unnoticeable, and because the actual amounts are probably rather uncertain.

--Emily

[rlorenz]

I get the idea that any time you have more than one carbon in a molecule, space scientists call it "a complex organic molecule."

And I think the press encourage that - they don't want to know the details or distinctions
anyway. After all, chemistry, like math, is hard......

There is also the issue of not actually knowing what the stuff is - as you get to higher masses
there are more and more molecules that have that mass (to within the mass resolution of
INMS, anyway) so it becomes ambiguous. If you have enough signal (e.g. with Benzene
at Titan) you can start using the cracking pattern to make identifications, but with the low
signal at Enceladus I expect that is pretty challenging.

[Stu]

Probably a dumb go-stand-in-a-corner question, but it's been nagging at me so I'll go ahead and ask it anyway...

Enceladus must have got in the way of quite a few Saturn-bound comets over the millennia, just by being in the wrong place at the wrong time, right? Is it possible that some of this "cometary chemistry" might be contamination of a kind? Traces of cometary material that found its way into the Tiger Stripes only to be spat back out again..?

That would have been a heck of a shot, wouldn't it? A comet crumps down near the south pole, splashing slush in all directions.. some slips and slithers down into the fractures... some of the slush contains cometary critters who can't believe their luck after finding themselves in a great place to live, all wet and warm and cosy...

Discuss.

[JRehling]

It may well be that Enceladus has a significant amount of cometstuff in it, but I think the basic explanation is that ices and volatiles make up a fair amount of the solid stuff at sufficient solar distances. Enceladus should be highly differentiated, at least where the plumes are, so this all seems more automatic to me than a surprise. I mean, it's not like there was going to be copper, silver, and gold sitting on top of slush and water.

I think there's a pervasive, tempting, and misleading tendency to think of accretion as having happened like a phase, having ended on some specific day and date, and then everything after that was A Collision (capital letters). There really should have been stuff in solar orbits slicing through the Saturn system constantly, with some mass exchanging in both directions. This would have happened from the very beginning, and only became less common gradually. So was Enceladus "hit by a comet"? Sure, quite a bit, I'm sure. How could it not?

I would only expect comets and Enceladus's lighter stuff to be different if comets formed out at some point where something was frozen, but that would melt at Enceladus's distance. I don't think there's a whole lot of matter that fits that category -- Enceladus is cold. Comets don't have a lot of frozen molecular hydrogen. What else would they conceivably have that Enceladus wouldn't?

The one thing we learn is that chemistry happened in comets and in Enceladus. Since the same reactions happen with the same compounds and the same elements, it's a rather minor surprise, I'd say. About all we learned is that stuff from a rocky core isn't coming out along with the wet stuff.

[brellis]

JReihling - thank you for your Post #116. You describe succinctly and in easily understandable terms a very complex process.

Regarding your mention of a common urge to explain a planetary condition through the prism of "A Collision": it would seem that the rings of Saturn itself, and - if they're really there - the rings around Saturn's moon Rhea, are in fact the result of one or more big collisions that left a swirl of debris. As you point out, it's unlikely that the comet-like content of Enceladus is the direct result of one or a few big collisions. Could it be an indirect result? Perhaps.

A question for the experts: do moons or planets at LaGrange points tend to tidy up a dusty ring, or are they more likely to keep a ring of tiny bits in place?

To rephrase, do the shepherd moons of Saturn have a specific L-point relationship that lets the rings survive, whereas the large moons of Jupiter have/had an L-point relationship that caused them to clear out the dusty rings?