With April 1st coming up, perhaps one of you academic types might dust off an old paper and re-submit it somewhere with the units all converted to things like hands, smoots, furlongs and fortnights.

"... Is the new highest temperature the average over the sensor footprint,... "

A surface that's an efficient emitter (near blackbody, like ice) that is all one temperature, puts out a blackbody spectrum. When you convert infrared brightnesses to estimated temperature, the estimates are the same at all wavelengths.

When you have an unresolved checkerboard mosaic surface with two temperatures, one cold and one warm, you get an average of two blackbody spectra and the result is NOT a blackbody spectrum of the average temperature. The warm surface emits more at shorter wavelengths and the cold surface emits more at longer wavelengths. You can model a checkerboard pattern to get the temperatures of the two components AND the proportions of the components. But there's slop in the modeling. Youi usually have more than two temperatures and varying fractions at the surface with temperature and there's just not enough data in the spectrum to tell you what's really going on.

At Enceladus, you probably have regional "cold" temperatures, possibly a generally "slightly warmed" surface between tiger stripes, "warm" surfaces matching the blue areas (in color pics) of the stripes, "hot" areas that are very close to the vents and "very hot" areas within the vents themselves.

If you do 2 component modeling with the better resolution of the new data, you can get the inter-stripe temperatures and in those regions model the mix of cold and slightly warmed surface, then over at the tiger stripes, model "slightly warmed" beside the stripes and "warm+hot" temperatures and coverage fractions on the stripes. If "hot" is different enough from "warm" and is abundant enought in the hottest appearing areas, you may be able to get a better overall fit to the data with 3 components and be able to report a "hot" temperature and estimated surface fraction.

Right now, they're probably NOT reporting that. In 2 or multi-component circumstances, just looking at the raw data, short wavelengths give warmer readings than long wavelengths. They're probably simply reporting the pixel-average temperature in the hottest pixel measured at the shortest wavelength where they have useful signal-to-noise. We can assume if that's correct, the 180 K reading is a lower limit to the real temperature of the hottest areas in the field of view.

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

... which is exactly the kind of thing I wanted to know.

On a related note, John Spencer's blog entry says the stripes were detectable even in the 7 micron wavelength range. That's pretty close to the 5 micron max VIMS can observe. I realize that's stretching it a bit too far, but would it be even remotely possible for VIMS to see the stripe thermal glow (as it can in case of Jupiter and Saturn, for example)?

I wonder if the VIMS S/N ratio is too low for this combination of instrument sensitivity and the wavelength a tad too short (likewise, temperature too low), or would it be feasible? I don't suppose VIMS was active during the outbound leg of the flyby, during the eclipse?

Nope, we fit the spectrum over all available wavelengths, with a single component filling a small fraction (typically about 1%) of each pixel. The rest of each pixel is too cold to radiate significantly in our short-wavelength detector. Pixel-averaged temperatures are much colder.

John.

"Nope, we fit the spectrum over all available wavelengths, with a single component filling a small fraction (typically about 1%) of each pixel. The rest of each pixel is too cold to radiate significantly in our short-wavelength detector. Pixel-averaged temperatures are much colder."

Modelling gets done faster these days. It sounds like this is close to a 2 component system.. cold background, radiating mostly at long wavelengths, and a tiny fraction of the surface at high temps. Is there any sign of an intermediate component.... say "hot but not really hot and actively emitting plume" general tigerstripe component, or would the estimated 1% pixel fraction include the entire "valley" part of the stripe within the pixel?

VIMS might be able to see the glow if there's a hottest component at or above that 180 K temp AND if it has high enough signal-to-noise AND if there's no sunlight. The sun's not very bright 5 microns, but on the shortwave flank of a blackbody spectrum, brightness drops FAST as your wavelength decreases and any solar interference would likely swamp any signal.

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.

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.

Interesting thought, Stu. You know that over the past 4.5By more then a few comets had to hit Enceladus, regardless of how small a target it is and given its proximity to Saturn (thinking of gravitational focusing here).

"Small" in fact might actually be the key point for Enceladus: could a significant amount of its original mass have been displaced into the E-ring and beyond by comet impacts over time? Framed in this way, it might be surprising if its non-core composition wasn't approximately cometary by now, though given that thought that might set some pretty severe limiting constraints on the moon's intrinsic chemical processes...

Damn. Now I gotta go drive 56,740 smoots in horrible traffic to perform Reserve duty instead of digging this thread. (I have taken an oath to express all personal terrestrial positional displacements from now on in smoots. Velocity will be expressed in furlongs per fortnight, which is not an unreasonable unit for LA traffic...)

This time of day in Los Angeles you'll probably be driving no faster than 200 furlongs per hour, meaning it's going to take 0.0119047619 fortnights to get there. So you better get going.

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.

"With April 1st coming up, perhaps one of you academic types might dust off an old paper and re-submit it somewhere with the units all converted to things like hands, smoots, furlongs and fortnights. "

I might be able to spare two shakes of a lamb's tail for that.

Phil

Hello everyone. This is my first post so I hope I'm not starting with a dumb question - are there more images to be released from this flyby? Congratulations to all involved with this site. Just awe inspiring. Al.

Welcome to UMSF! To answer your question, all images from the flyby have been released on the Cassini Raw image site: go to http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm and search for Enceladus. There weren't many close-up images because Enceladus was in Saturn's shadow after the flyby. Nice mosaics and color versions of most of the best images have been either released on the official Cassini site (just the approach crescent mosaic) or right here. There will be lots more images on the next flyby, on August 11th this year.

John.

Many thanks for the warm welcome and info John. My insomnia is currently being fuelled by thoughts of what the August flyby will reveal and the Pluto Kodak moment !!!!!!!Al.