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Posted by: ugordan Nov 22 2005, 09:06 AM

I guess the news belongs to the Mars forum as well, but since I'm more of a Huygens guy myself, I figured this is a better place:

http://www.esa.int/esaCP/SEMA96ULWFE_index_0.html

Posted by: alan Nov 22 2005, 02:03 PM

Does this mean the Nature articles are about to be released too?

Posted by: DDAVIS Nov 22 2005, 02:58 PM

Doggone well about time. I would like to see the final image mosaics from Huygens, with color overlays from the spectral data, as we saw in the test images.

Don

Posted by: ugordan Nov 22 2005, 03:23 PM

I wouldn't hold my breath for color mosaics like that, they would need pretty accurate reconstruction of where the spectrometer was looking at (not that it samples only a single point, rather it averages the entire FOV, IMHO). In any case, the color resolution would probably turn out very low and the whole scene uniformly colored, sort of like that one uniformly hued surface image.
I seem to remember Marty Tomasko saying that most of the spectra they've taken is very similar.

Posted by: DDAVIS Nov 22 2005, 04:34 PM

[quote=ugordan,Nov 22 2005, 03:23 PM]
I wouldn't hold my breath for color mosaics like that, they would need pretty accurate reconstruction of where the spectrometer was looking at (not that it samples only a single point, rather it averages the entire FOV, IMHO). In any case, the color resolution would probably turn out very low and the whole scene uniformly colored, sort of like that one uniformly hued surface image.


Perhaps, but this test image, at:

http://www.lpl.arizona.edu/~kholso/images/bashar/mosaic_c_3.jpg

shows some resolution of color information. In addition, the quality of the images in the tests seems to be suspiciously better than the performance of the flown camera. I suppose low contrast in the Titan view provided an opportunity for compression artifacts to have a field day.

Don

Posted by: ugordan Nov 22 2005, 04:54 PM

Not to mention that 7 years of cosmic radiation damage to the CCD had also done its job. Also, the test images were taken from a low altitude and they (the team)were able to provide complete coverage of the area beneath by rotating the camera. Huygens' descent was pretty much chaotic tumbling...

Posted by: DDAVIS Nov 22 2005, 07:21 PM

[quote=ugordan,Nov 22 2005, 04:54 PM]
Not to mention that 7 years of cosmic radiation damage to the CCD had also done its job.

Were those CCD cameras markedly more sensative to Cosmic Rays than those used in Cassini or Galileo? I might expect distinctive defects on each and every frame of the three Huygens cameras caused by 'hits' on the CCD.



Also, the test images were taken from a low altitude and they (the team)were able to provide complete coverage of the area beneath by rotating the camera. Huygens' descent was pretty much chaotic tumbling...


Certainly, and they lost half the pictures due to a screw-up, I am not talking about coverage so much as inherent quality of the returned images. If you look at the test image mosaic, at:

http://www.lpl.arizona.edu/~kholso/images/team_images/h3_500_big_merc.jpg

you can see the sky at top displaying nominal gradations of brightness, which along with the rest of the image reveals little visible compression artifacting. Was the compression ratio in the earthbound tests the same as that actually used during the mission?

Don

Posted by: ugordan Nov 23 2005, 08:28 AM

I don't believe the CCD was more prone to radiation than other CCDs. If you look carefully at the raw images, you can clearly see a pattern of persistent noise on every frame. This can always be divided out if you have an appropriate flatfield image, but the compression artifacts make this somewhat difficult. The resolution of the CCD itself is nothing near the other cameras so the blemishes on individual pixels are more visible.
The contrast at Titan is markedly lower than the scenery on Earth so the raw images needed to be contrast-stretched quite a bit, of course also stretching and enhancing compression artifacts (which get bad with random noise introduced into the image).

Posted by: The Messenger Nov 23 2005, 09:10 PM

If I am interpreting the design documents correctly, there should be an index of the compression rations, jpeg schemes (and filtering) of each image; so the imaging team may have been able to bring out more details - we should know after the data release on the 30th. Don't expect miracles - Huygens was operating in very poor, virtually shadowless light. I think we stand to learn a lot more from the other instruments.

Posted by: ugordan Nov 30 2005, 03:20 PM

Several results on Mars Express/Huygens are now available online at:
http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/

Posted by: SigurRosFan Nov 30 2005, 03:32 PM

All Huygens Results (five press releases)

http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEMSCVULWFE_0_ov.html

Posted by: elakdawalla Nov 30 2005, 04:19 PM

Is anyone else watching the NASA or ESA TV feeds? I was looking hard for what's new in the results they were talking about. I think there were some nuggets of new-ness but I fear I'm going to have to read the actual Nature papers carefully before I will be able to write anything coherent about it. At least there are some new graphics on the ESA site:

HASI graph of impact:


Lower atmosphere wind speed and direction data from DISR:


Also, Jonathan Lunine showed the DISR team's attempt to match their mosaic to the RADAR images; I really hope that graphic shows up on JPL's website. One big difference between his stuff and René Pascal's is that the outermost tiles of the mosaic are stretched much longer, making some of those dark stripes line up with RADAR features quite neatly....

--Emily

Posted by: dvandorn Nov 30 2005, 04:34 PM

Ought to go into one of the Mars forums, I think, Marz...

For those of you who have been watching this press conference on NASA-TV on streaming video, y'all may be interested in the fact that I'm watching NASA-TV on cable and what ESA is sending out to NASA-TV is not even a video feed. It is, itself, nothing more than a streaming video from a webcam! They have all these wonderful graphics and charts and videos -- and all of them are on a 100k (or less) Real Player stream out to NASA-TV. And it's going to black every minute or two (I imagine so that their Real Player can re-buffer the stream).

It doesn't even have enough resolution to be able to read the PowerPoint slides -- which make up 90% of the visuals they're presenting.

For those who have been defending ESA's PR effort -- you *cannot* convince me that ESA has the money to mount planetary missions but lacks the money to provide a *watchable* video feed of their "triumphant" release of Huygens and Mars Express data.

This is totally, completely lame.

-the other Doug

Posted by: JRehling Nov 30 2005, 04:59 PM

Combining the GCMS data, I get the following atmospheric composition (which is a form I like to see this data in, but ESA refuses to do the math!)...

Incidentally, I get different results if I sum the apparent CH4 isotopes in the GCMS chart than the ESA graph which reports just N2 and CH4. They may not be counting CH4 isotopes in the latter? The table below uses the CH4 count from the time of landing (not later, when CH4 abundance rose, apparently due to the spacecraft warming the ground) and ESA's CH4 count from the N2-CH4 chart. Clearly, the levels of CH4 are variable, and are thus more like H2O in Earth's atmosphere -- highly variable, and usually not reported in atmospheric composition of "dry" air.

N2 90.4%
CH4 9.2%
H2 0.32%
Ar-40 0.011%
CO2 0.009%
C2H6 0.007%

If you discount CH4 from the total, then N2 ends up as 99.6% of the total, with the other gases getting values about 1.1 times that reported above.

Posted by: SigurRosFan Nov 30 2005, 05:09 PM

PIA06435: Huygens Landing Site (Animation)

http://photojournal.jpl.nasa.gov/catalog/PIA06435

--- This movie shows a quick succession of multiple products of Titan's surface from the Cassini orbiter and the European Space Agency's Huygens probe. It shows Cassini imaging science sub-system images, radar images and visual and infrared mapping spectrometer images of the Huygens probe landing area. The rest of the movie consists of mosaics from the descent imager/spectral radiometer. The camera system on the Huygens probe mimics the descent profile of the probe starting at about 144 kilometers (89 miles), looking eastward throughout. It displays the Titan surface in true color. The sequence ends with a true-color surface image. The radar images of the Huygens landing site were taken by the Cassini orbiter radar instrument during the Titan flyby on Oct. 28, 2005. ---

Posted by: RedSky Nov 30 2005, 05:15 PM

I also started watching it on my local cable which has NASA select. I really was dumbfounded by the streaming webcast quality, esp in the poor audio. Then, when the tech at his laptop running the slides couldn't start the mpeg animation of huygens 2 minutes into the press conference, and it took 5 minutes just to fiddle around to get the images up, I thought... ugh! Very amateurish... how High School. Sad to say, but public opinion does depend on how organized you seem, especially in the simple things. It's not like this was a hastily put together conference.... like what might be expected on the day of the landing. This conference was planned for some time, and should have been better organized.

One other thing I noticed. Maybe its just me, but the presenters really didn't seem all that excited. They just sort of matter of fact read their powerpoint bullets. I've seen some of the driest, esoteric stuff presented at some NASA conferences, but because of the presenter's excitement about the results, you sort of felt they really were important. Here, it just seemed like a board room conference, with each member giving his little bit. It seemed too much like a job for them... they just didn't seem to have the passion. Or maybe its just my impression.. different cultures, etc.
I finally stopped watching after a half hour, so maybe things picked up later on.

Posted by: Phil Stooke Nov 30 2005, 06:12 PM

That business of the outer parts of the DISR mosaic being at a different scale goes back to my earlier message (too lazy to go back and find it!) about map projections. Rene's mosaic and the radar image are in different projections. Lunine is correcting for that. But you heard it here first!

Phil

Posted by: AlexBlackwell Nov 30 2005, 06:14 PM

The December 1, 2005, issue of Nature is now http://www.nature.com/nature/journal/v438/n7068/index.html.

Posted by: AlexBlackwell Nov 30 2005, 06:25 PM

Actually, the December 1, 2005, issue of Nature only has a http://www.nature.com/nature/journal/v438/n7068/full/438538a.html. The Huygens-related papers are being published on http://www.nature.com/nature/journal/vaop/ncurrent/index.html before being assigned to a later issue.

Posted by: JRehling Nov 30 2005, 06:29 PM

I just don't know how the CH4 is being tallied. I've seen two ESA sources put it at about 4.9%. Fix the methane thusly, and my table would read:

N2 94.7%
CH4 4.9%
H2 0.3%
others not really changed

Posted by: volcanopele Nov 30 2005, 06:59 PM

A few comments:

That issue would be next week's issue :-D

JRehling, that's about right. I was about to comment on your 9.4% total for CH4. Glad I remembered to read all the comments in the thread before posting.

Emily, the cat scratches to the north really helped!

Posted by: AlexBlackwell Nov 30 2005, 07:13 PM

Yeah, I guess today's press conference technically "lifts" the embargo

BTW, have you seen the proposed cover? Assuming they use the one I saw, I'd say it's pretty cool.

Posted by: tfisher Nov 30 2005, 07:13 PM

I'm going to have to run down to the university library to get online access to the nature articles. Meanwhile, let me share my latest iteration at trying to composite ISS narrow angle images of the Huygens landing area:

The small red star marks the currently announced landing site (see http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEMTFSULWFE_1.html#subhead1) of 192.3 degrees west, 10.3 degrees south.

The image is a weighted average of 10 images from the Ta and Tb passes, map projected to coordinates based on the kernel information in the PDS data release, and with alignment corrections (additional translation) as follows. (I don't know a correct benchmark to base coordinates off of, so the whole coordinate grid is probably off by some amount).

Image: n1477488603_2 Lat. correction:0 Lon. correction:0
Image: n1477488635_2 Lat. correction:0 Lon. correction:0.0135
Image: n1477488667_2 Lat. correction:-0.0675 Lon. correction:-0.018
Image: n1477488834_2 Lat. correction:0.0135 Lon. correction:-0.1080
Image: n1477488866_2 Lat. correction:-0.018 Lon. correction:0.0090
Image: n1477491536_2 Lat. correction:-0.0315 Lon. correction:0.0225
Image: n1481624204_4 Lat. correction:0.045 Lon. correction:-0.1575
Image: n1481624244_4 Lat. correction:0.0855 Lon. correction:-0.4005
Image: n1481624383_4 Lat. correction:0.036 Lon. correction:-0.0315
Image: n1481624423_4 Lat. correction:0.0315 Lon. correction:0

This is a work in progress still -- there are this many images again I want to stack together, I haven't removed noise from cosmic ray hits or bad pixels/charge bleeding, and I won't swear my alignment corrections are yet 100% correct.

Posted by: SigurRosFan Nov 30 2005, 08:27 PM

Finally ... Exactly located!!

Great work, Travis!

Travis vs. René

Click for larger version (606.5 KB, not to scale):
http://xs57.xs.to/pics/05483/Huygens_Landing_Site1.jpg

Posted by: volcanopele Nov 30 2005, 08:56 PM

See comparison with RADAR:

http://photojournal.jpl.nasa.gov/catalog/PIA06437

Posted by: volcanopele Nov 30 2005, 09:02 PM

A great deal of additional data has been posted on the DISR website:

High altitude mosaic including the SLIs showing cat scratches (further evidence in my mind that these are more like traditional longitudinal dunes, and not so much like antarctic megadunes):
http://www.lpl.arizona.edu/~kholso/titan_high_alt_051112_new.jpg

Landing site poster (more indepth on landing site identification)
http://www.lpl.arizona.edu/~kholso/landing_site_poster_2.jpg

Large version of Descent movie (warning: 300 MB)
http://www.lpl.arizona.edu/DISR_data/Descent_On_Titan_1.avi

Posted by: BruceMoomaw Dec 1 2005, 05:27 AM

Notice how many yummy substances there are on Titan's surface? Hydrogen cyanide, cyanogen, benzene, maybe ethylene... mm, mm, good.

One of the biggest questions in Huygens' wake seems to be what that "mystery substance" is that produces the near-IR spectrum which it recorded for the surface material. Could it be the acetylene polymers which have frequently been talked about? (The fact that Huygens picked up definite whiffs of benzene vapor --despite that substance's very high boiling point -- suggests that there's a hell of a lot of it there; and benzene is supposed to be one common result of acetylene polymerization.) At any rate, I still think the ESA missed a serious bet by not replacing most of those silly Surface Science Package sensors -- which, as the article says, would have worked just fine if there had happened to actually BE any liquid there -- with a heated core tube hooked up to the GCMS, in the same way that France's cloud pyrolyser was. Had they done that, we'd know vastly more about Titan's surface makeup than we do now -- or than we would have known even if it had landed in liquid with the SSP sensors.

The other biggest question (which caught me by surprise) seems to be whether they actually did detect indications of lightning, or some other ionospheric phenomenon.

Posted by: JonClarke Dec 1 2005, 05:48 AM

Even if you are right this is 20/20 hindsight. The package has yielded useful data and valuable insights into the surface of Titan. Therefore it was not silly.

Jon

Posted by: BruceMoomaw Dec 1 2005, 07:35 AM

Not very much "useful data", except for the penetrometer (designed by Ralph Lorenz, by the way) and the accelerometer. These were the only surface sensors planned for inclusion on Huygens during its initial development in the late 1980s -- the surface analysis would have been done by that heated core-tube concept. Include that device (which of course could also have analyzed liquids), and the only other SSP sensors worthy of being included would have been the echo sounder and the tilt sensor. I still maintain that the SSP was the ESA's one significant mistake in designing this mission.

Posted by: JonClarke Dec 1 2005, 08:26 AM

Not much useful data?

The SSP contained nine instruments that had to cover the full range of possible surfaces that might have been encountered, based on knowledge available at the time.

The nine instruments were:

1. Impact accelerometer X 2
2. Tilt sensor
3. Thermal properties sensor
4. Acoustic velocity
5. Acoustic sounder
6. Fluid permittivity sensor
7. Fluid density
8. Refractometer

Six of the nine (1-5) returned useful data. The other three (6-8) have been less successful because they were designed to analyse fluids that were not at the landing site. But some information may still be obtained from them.

Given the range of possible conditions the package had to be designed for I think this is very good result. If we were to design another mission now we would to it differently. But that is experience.

There is no way that the choice of instruments can be called silly based on the results or on what was known when they were selected.

Jon

Posted by: BruceMoomaw Dec 1 2005, 09:52 AM

Once again: all of them except the penetrometer and accelerometer were based entirely on the assumption that Huygens would land in liquid -- and all of those except the tilt sensor and echo sounder used various physical properties of that liquid to try to deduce, with some degree of accuracy, its composition. This, to put it mildly, is going around Robin Hood's barn -- that heated core tube hooked up to the GCMS would have provided a tremendously more detailed analysis of the surface material whether it was liquid or semisolid. (If the surface was too hard for the core tube to penetrate it on impact, the tube could easily have been designed so that it would do no dmage to Huygens -- just like the penetrometer shaft, to which the tube could probably have been attached.)

As it was, except for the two surface hardness sensors, the remaining sensors (or, rather, some of them) only got some very limited data on the physical properties of the atmosphere and the smoothness of the terrain near the landing site, which, -- where science value is concerned -- doesn't begin to compare with a surface analysis. There may be some esoteric scientific explanation for why the SSP sensors were ultimately chosen instead; but I wouldn't be surprised to learn that they were chosen for institutional reasons instead -- that is, the SSP sensors were simply what Britain's Open University insisted on providing (perhaps due to the particular expertise fields of its scientists), and ESA's multinational nature forced it to accept that particular payload as a contribution from Britain. If possible, I intend to find out more about this question.

Posted by: ljk4-1 Dec 1 2005, 03:08 PM

Nancy Neal Jones
Goddard Space Flight Center, Greenbelt, Md. November 29, 2005
(301) 286-0039 1 p.m. EST

RELEASE: 05-53

TITAN'S MYSTERIOUS METHANE LIKELY COMES FROM INSIDE, NOT THE SURFACE

The methane giving an orange hue to Saturn's giant moon Titan likely comes from geologic processes in its interior according to measurements from the Gas Chromatograph Mass Spectrometer (GCMS), a Goddard Space Flight Center instrument aboard the European Space Agency’s Huygens Probe. The GCMS, which descended with five other instruments on the probe through the moon's thick atmosphere on Jan. 14, 2005, also found evidence of liquid methane in the surface material.

Methane, a molecule consisting of four hydrogen atoms bound to a carbon atom, is the primary component of natural gas on Earth. It can be produced by life, by degradation of organic debris or by geologic processes like volcanoes.

The origin of methane in Titan's atmosphere is a mystery because it gets broken down by sunlight and particle radiation from space in the upper atmosphere. If surface lakes and pools were the only source, all of Titan’s methane would be lost by this mechanism in less than a hundred million years, a short time for a moon that's been around since the formation of the solar system 4.5 billion years ago. Components of the methane molecules react with each other and atmospheric nitrogen. As they descend, they form larger and heavier molecules that comprise the orange haze that blankets the moon. Because Titan is very cold (292 degrees below zero F, or minus 180 degrees Celsius) these heavy compounds condense and rain out on the surface.

"We have determined that Titan's methane is not of biological origin, so it must be replenished by geologic processes on Titan, perhaps venting from a supply in the interior that could have been trapped there as the moon formed," said Dr. Hasso Niemann of Goddard, principal investigator for the GCMS and lead author of a paper on this research to appear in Nature on Dec. 8. An advance online publication will be available on Nov. 30 at


http://www.nature.com/nature/index.html.

Posted by: paxdan Dec 1 2005, 04:18 PM

Bean, Beans, good for the heart... etc etc etc..

Posted by: JonClarke Dec 1 2005, 09:51 PM

Once again, you are arguing with 20/20 hindsight. At the time the instruments were chosen it a was widely considered that Titan could have a partly liquid covered surface. I assume you are familiar with this literature? The SSP instruments were selected by a competitive process to cover as many possibilities for the landing site as it could, dry, slushy and wet. Including a wet surface (which may still be valid for some parts of Titan and some times This was the right choice for what was known then, not a silly one.

Once again, because the surface was unknown and the package was so well designed to cover all possibilities it has yielded useful results and will continue to do so. Therefore it was not silly.

Once again, if we were sending a lander to Titan now, we would send different instruments. We would also have some idea what we were landing on, rather than having to cover all possibilities. This is part of the learning exercise.

Or are we going to label the Viking life sciences experiments silly because the surface turned out to be lacking in organic molecules and laced with oxidants? It would have been much better to have sent a microanalytical wet chemistry lab and and XRD. we would have learned so much more about the surface!

Jon

Posted by: mike Dec 1 2005, 10:27 PM

Yeah, and why didn't everyone here buy all the Google stocks they could when they first opened? Or oil futures before they shot way up? Or Microsoft when it first opened? Or pick the winning numbers for the most recent lottery, or the one before that, or the one before that, or or or or ..........

Posted by: BruceMoomaw Dec 1 2005, 10:32 PM

Clearly we're going to slug this one out interminably, but... to repeat, the GCMS core-tube suggestion (which, as COMPLEX pointed out in 1988, was what the ESA was planning back then), would have worked to analyze even a liquid surface better than the various composition-oriented sensors in the final SSP package, although the remaining sensors oriented toward a possible liquid landing (the tilt meter and the echo sounder) are perfectly defensible. There is still something puzzling about this story.

Posted by: JonClarke Dec 2 2005, 12:44 AM

Actually, we are quite close I think. Sometimes the reasoning why some instruments make it and others don't is obscure. Don't get me started on Mossbauer or atomic force microscopy.... But even here there are defensible reasons even if I don't entirely agree with them!

Jon

Posted by: BruceMoomaw Dec 2 2005, 02:39 AM

One other thing: replace the five composition-oriented SSP sensors with that core tube, and you might have had enough room left for a few more useful post-landing sensors (Anemometer? Precipitation sensor?)

By the way, one sensor that WAS originally part of the SSP but got the boot due to development costs was an X-ray spectrometer from the U. of Chicago that would presumably have tried to analyze any fragments of actual silicate rock that turned up on the surface (XRS can't detect any element lighter than sodium). They must have concluded that the chances of this were unlikely.

Posted by: BruceMoomaw Dec 2 2005, 02:45 AM

There's no point in jumping up and down on ESA endlessly for this -- they DID unquestionably pull off a major scientific triumph -- but it's going to be a while before we get another look at Titan's surface. (The earliest possible date at which the next spacecraft can land on Titan is now 2023, and you can almost certainly tack another 4 or 5 years onto that.)

Posted by: The Messenger Dec 2 2005, 04:08 AM

OK, so what are the non-biological synthesis roots for methane?

Posted by: BruceMoomaw Dec 2 2005, 07:04 AM

The leading theory is that it was through "serpentinization" -- the same process that's the front-runner to explain Mars' traces of methane. That is, the rock in Titan's carbonaceous-chondrite core is exposed to water at high temperatures, setting off a reaction that turns the basalt into serpentine minerals and releases hydrogen -- and the hydrogen then reacts with the large amounts of elemental carbon in the rocks to produce methane. That methane, in turn, is gradually transported from the core up through the ice mantle to the surface by the same cryovolcanic processes that have thus transported the argon-40 which comes from the decay of potassium-40 in the rocky core.

It's also been speculated that some of Titan's interior methane may have instead been trapped in its core at the start, as Niemann said -- having originally been incorporated as methane clathrate in the ice chunks which also helped form Titan. Another possibility is that the carbon was first deposited in Titan's ice as carbon monoxide clathrate, with the CO in the ice later reacting with that hydrogen released by core serpentinization to form methane.

Posted by: elakdawalla Dec 2 2005, 05:54 PM

I just noticed this up on Photojournal. This is the view that Jonathan Lunine talked about at the press conference yesterday, with the DISR mosaic overlaid on RADAR imagery (lucky guy -- he gets to work on both teams!) You can see how they were able to use some cat scratches to line the map up.



You can compare it to the view of just RADAR imagery at http://photojournal.jpl.nasa.gov/catalog/PIA03569. I sure wish they'd release that landing site RADAR image without the squiggly yellow outline on it! If I'm not mistaken, the yellow outline doesn't quite match the newest determined position of the huygens mosaic -- right?

--Emily

Posted by: tfisher Dec 2 2005, 06:01 PM

You're right -- the location moved. There are much better RADAR images without the annoying yellow outline in the poster volcanopele pointed out on Kholso's page... http://www.lpl.arizona.edu/~kholso/landing_site_poster_2.jpg.

Posted by: volcanopele Dec 2 2005, 06:08 PM

Yeah, it moved a bit to the NE. BTW, I want to thank Rene for his mosaics which helped.

Posted by: elakdawalla Dec 2 2005, 08:48 PM

I'm making headway on creating a single Web page that hosts all the most useful images and data from the Huygens descent, both official and amateur: http://planetary.org/explore/topics/saturn/titan_huygens.html incorporates all the graphic files I could get my hands on. Next step is to run through all the Nature articles and pull out the quantitative data on atmospheric abundances, etc. Please let me know if the page is missing any published graphics! In particular, has anybody seen the SSP penetrometer data from the impact on the Web anywhere, apart from within the Nature publication itself? (I've asked permission to use that one and am waiting for a reply.)

--Emily

Posted by: Bob Shaw Dec 2 2005, 08:54 PM

Ask Tommy Gold!

Bob Shaw

Posted by: RNeuhaus Dec 2 2005, 09:09 PM

After viewing pictures from the planetary.org posted by Emily, I am thinking that it is incredible that Huygen had landed safely on a very rough land. On the other words, that land is not like a plain desert like to Terra Meridiani where Oppy landed very easy.

Nobody must not discuss anymore about the incomplete science collection, specially to Bruce's complains about missing of some useful instruments.

Hence, I think that there was a very high risk that Huygens would be smashed on any hillside and miss all scientific data that would be sent back to Earth.
Rodolfo

Posted by: Matt Dec 2 2005, 09:48 PM

Agreed. Huygens really was going into the unknown, and there were just so many things that could have gone wrong.

In terms of the probe actually making it safely to the surface, not to mention returning data from the surface for over an hour........I think that was an incredible acheivement. The greatest achievement in the history of Solar System exploration if you ask me.

Posted by: JRehling Dec 2 2005, 11:48 PM

Well, in many ways, Titan is actually the *easiest* place in the solar system to land. The low gravity and high, thick atmosphere makes the process of decelerating from space to the surface easier than anywhere else. The long cruise and the cold (esp. in comparison to a Venus flyby the craft had to undertake), as well as a more difficult radio link than elsewhere are the factors that made it hard, but I would still bet on ten Titan lander attempts to field a better success rate than ten Mars landers or ten Venus landers. To have a Jupiter entry probe survive for over two hours is a greater feat in terms of engineering. And in terms of sheer complexity, the Apollo missions are in another realm. And check out the four Viking craft.

The choice of instruments is another matter -- the craft would have survived whether there'd been a different surface package. I don't have any 20-20-hindsight daggers to throw at the team on that count. If Titan were in the inner solar system, we could have staggered probes at 2-year intervals, adding more instruments as we go. It was right to throw a big suite of instruments at Titan on this go-around, even if some ended up of little or marginal use.

Posted by: BruceMoomaw Dec 3 2005, 11:35 AM

Oh, I agree. I just think that in this one respect it was the WRONG big suite of instruments, and that this could have been foreseen to be true no matter what kind of possible surface existed.

And I agree that Huygens was remarkably lucky in its landing site. Not only might it have landed on one of those steerp arroyo slopes (30 degrees) and rolled or bounced downhill, but it happened by luck to land in the one place -- just beyond a lakebed's shoreline -- that would allow us to understand clearly just what kinds of overall processes are actually occurring on Titan.

About 10 years ago I concluded that Titan has the strange distinction of being the only world in the Solar System that's actually easier to land on than Earth. Not airless (or almost airless like Mars) so that you need a rocket-propelled landing system; not as savagely hot as Venus, so that the lander needs a thickly insulated pressure hull just to survive briefly; a slower entry speed than for Earth, and also an atmosphere much thicker relative to the world's surface gravity, allowing a far smaller parachute to be used...

It should also be kept in mind that Titan is the only other world upon whose surface a human can walk without a pressure suit -- all you need is a properly insulated and/or heated coverall, and an oxygen mask.

Posted by: Bob Shaw Dec 3 2005, 11:57 AM

Bruce:

Very true - *but* I think you'd need to be very cautious with regard to chemical reactions as a result of leaks from your oxygen mask into the outside environment, or the gasses that'd percolate into your nice warmsuit and then invade your equally nice spacecraft!

Bob Shaw

Posted by: The Messenger Dec 3 2005, 02:47 PM

Thanks, Bruce. That would mean internal termperatures >500K, which shouldn't be too surprising anymore, given the display Enceladus is putting on.

Posted by: alan Dec 3 2005, 05:31 PM

Has there been any mention of which direction Huygens was facing when it landed?

Posted by: elakdawalla Dec 3 2005, 05:44 PM

Yes. From the DISR team's paper: "the last upward-looking spectra indicate that the probe settled with DISR facing southward."

--Emily

Posted by: dilo Dec 3 2005, 10:27 PM

Hi all. I made some work on the new released image mosaic from the soil...
In particular, I further extended the lower portion image, taken by the Medium Resolution Imager (MRI) and now showing the region overesposed by illuminator:

Then, as usual, I made a vertical projection (assuming an camera height of about 35cm above the soil); it is showed with 2 different scales

Considerind these view are toward South, they should be put upsidedown in order to eventually match descent mosaics... any volunteer interested to identify features?
Emily, maybe these two images can be usefull for your website...
Marco

Posted by: The Messenger Dec 4 2005, 04:06 AM

http://www.newscientistspace.com/article.ns?id=dn8395

This can't be right, can it? The preliminary presentations I have seen, seems to show an atmospheric density of ~1.6e, as expected. What is the density of the surface atmosphere of Titan the Huygens team is reporting?

http://www.mrc.uidaho.edu/~atkinson/Huygens/DWE_Presentations/Bird/

Emily - there is also a good image of the penetrometer data on one of the slides, but you might need Atkinson's permission to post it. (Bonn presentation p 28)

Posted by: alan Dec 4 2005, 04:38 AM

The pressure is 1.6x Earth's atmospheric pressure. Since the tempreature is lower the density should be more than that although I doubt 10x is right.

Posted by: elakdawalla Dec 4 2005, 05:19 AM

I know for a fact that there are several diagrams in those powerpoint presentations that Dave Atkinson and Mike Bird regard as "unpublished." I wonder if they realize that those URLs are available to the public -- or at least to Google? I'm going send Dave an email about that...anybody who wants them, better download them before Dave checks his email but be nice and don't "publish" any of the diagrams!

--Emily

Posted by: JRehling Dec 4 2005, 06:18 AM

I think the 10x factor is accurate for the *mass* of atmosphere over a given unit area.

The derivation is thus: 1.6 times the *weight* of atmosphere over a given unit area (that's the pressure), but 1/6 the gravity. 1.6 times 6 ~= 10.

My guess is that the mis-use of "density" is journalistic "license".

Posted by: elakdawalla Dec 4 2005, 04:00 PM

Here's the end of the timeline from J-P Lebreton's Nature paper. "The probe’s channel A carrier signal was still being received on Earth by radio telescopes at the time of the planned completion of the observations, at 16:00 UTC (Earth received time), meaning that the probe was still operating at 14:53 UTC (Titan time). Post-flight analysis of the probe telemetry data indicates that the batteries probably became fully discharged at about 15:10 UTC, a mere 17 min after the Huygens radio signal was last verified on Earth. It is thought that the probe continued to function until the batteries were exhausted."

Surface impact 11:38:11 UTC (T0+2:27:50)
End of Cassini-probe link 12:50:24 UTC (T0+3:40:03)
Probe support avionics power-off 13:37:32 UTC (T0+4:27:1)
Last channel A carrier signal reception by Earth-based radio telescopes ~14:53 (16:00 Earth received time) UTC (T0+~5:43)
Probable full discharge of Huygens batteries ~15:10 UTC (T0+~6:00)

You can see the full timeline at the bottom of http://planetary.org/explore/topics/saturn/titan_huygens.html.

--Emily

Posted by: dilo Dec 4 2005, 06:08 PM

Coulored version (preserving general hue..)

Posted by: JRehling Dec 4 2005, 06:25 PM

That's very good. They should have done this in the original release instead of the one-hue-fits all image. I'm not sure how you went about it, but it seems not too "fictitious" to vary saturation inversely with brightness. No worse than making the whole world peach-colored.

Incidentally, you say "general hue". There is data presenting the spectrum from green to IR in the light of the lamp (not through the orange haze). It looks a lot like the brown you used. (Blue is not available, but that can be extrapolated at some hazard.)

Posted by: dilo Dec 4 2005, 08:50 PM

I simply assumed that, if rocks are made of water ice, they should tend to a white color... moreover, I differentiated color between flat and taller rocks, only in order to vary their appearance (don't know if they really have a different origin or composition).
Wath about the sky? maybe should improved...

Posted by: mike Dec 4 2005, 09:15 PM

That does look much better than the versions released so far.. regardless of whether Titan really looks like that or not (and nobody knows, for quite a few years anyway), it looks more believable.

Posted by: Olvegg Dec 4 2005, 09:24 PM

True-color version of surface image was released with the landing movie:
http://saturn.jpl.nasa.gov/multimedia/videos/video-details.cfm?videoID=102

Posted by: dilo Dec 4 2005, 09:51 PM

Thanks, Olvegg, I already watched to this video. Contrary to first color released image, this one appear very contrasted and shifted toward red (while they declared a mean general hue of 22.5, here maximum is centered at 20 and terrain without rocks is even lower)...terrain appear very dark red and rocks are yellower and less saturated... frankly, it seems too much Mars-like panorama!
How/why/when they changed colors estimation?

Posted by: Olvegg Dec 4 2005, 10:35 PM

Did they mean surface image hue? If so, where from did they get hue 33 for the first color image?
As for new colors - reddish colors may be more consistent with hydrocarbons than yellowish ones.

Posted by: The Messenger Dec 5 2005, 04:25 AM

When I plug these numbers into the perfect gas law and assume a mole eq wt of 28 for both atmospheres (Earth and Titan), I get 8x the earth density @ 1.6 atmospheres, and 7.3 @ 1.46 atmospheres (earth). Since we are not dealing with quite perfect gases and the moles are just rough estimates, "10x the Earth density" could be very close to correct.

Posted by: The Messenger Dec 5 2005, 04:40 AM

Dave's presentation folder has been on line for several months, so he should know that it is 'out there'. (I don't know if they 'google', I was referred to it by a team member.) The presentation slides raise more questions than answers. For example, the radar plots are just a mess, and there is no correlation with the mission time scale. I hope the Nature article will finally clarify many things. The ESA's reticence at releasing fully qualified data is dishearting.

Posted by: JonClarke Dec 6 2005, 12:29 AM

More gratuitous ESA bashing, give it a rest folks!

Back to this nice image, which apporaches the resolution of the one in the Nature paper by Tomasko et al. paper, although that is B&W and mas a less washed out background.

Several interesting features are evident: 1) The pebbles in the mid distance appear to have tails to them, indicating fluid flow from left to right. 2), the tilted pebbles on the far right. 3) the pebble on the extreme left foreground is cracked, 4) the closest pebbles looks as if it might have been moved slightly to the right. 5) the pebble-covered ground in the foreground and distance.

Some comments:

1) Tails: Assuming thewere deposited by liquid, this means that the flow would have been the upper flow regime for the fine sand sized particles, but not enough to move the large pebbles.

This raises the interesting question of how the pebbles got there. Were they transported by previous, higher energy floods? Or by some other process, such as rafting (what floats in liquid methane?)? Or are they the result of vertical transport through the substrate? I have seen all three in desert channels.

of course the tails may be due to wind action. I am notsure if we can tell wind from fluid tails at this stage.

2) Could the tilted pebble be due to imbrication from fluid flow? if so, the flow direction is consitent with that of the tails - from left to right.

3) and 4) Could the cracking and movement be due to the probe's landing? Or is indicative of site processes? Cracking suggests volume changes, perhaps thermal. What is the diurnal and seasonal temperature range on Titan? Would it cause exfoliation in ices?

Indigenous movement suggests creep, perhaps driven by volume changes in "soil". What causes volume changes in Titan's "soil"? temperature? "Wetting" and "drying" by liquid methane etc? If indigenous, is it coincidence that movement has been towards the left, consistent with the flow observed in 1) and 2)? Or does it point to a general slope?

5) Pebbles: What is the formation of the pebble rich foreground and background? Are typical of the landscape between channels? In which case what has formed the ice gibber armour - deflation, vertical movement? Or are they gravel bars in a larger channel system? Their rounding suggests transport, but maybe Titan weathering can ground rocks as well.

Jon

Posted by: JonClarke Dec 6 2005, 01:00 AM

Don't forget that the gravity is lower, so the pressure of a given atmospheric density will be lower as well. 1.6 atmospheres divided by 0.14 G gives 10.7, which is close enough for New Scientist. Or am I totally barking up the wrong tree? Some would argue I am just plain barking....

Jon

Posted by: exoplanet Dec 6 2005, 02:50 AM

[quote=JonClarke,Dec 6 2005, 12:29 AM]
More gratuitous ESA bashing, give it a rest folks!

Jon,

All of us here (within limits) feel comfortable enough with each other to freely critique ESA or NASA at will if needed. I for one am sorely disappointed with the slow image releases and data from ESA's Mars Express.

"This raises the interesting question of how the pebbles got there. Were they transported by previous, higher energy floods? Or by some other process, such as rafting (what floats in liquid methane?)?"

Something may be masking any specular glints of surface liquid. There may be a possible explanation that the liquids (methane and ethane) that should be seen on the surface have some sort of chemical interaction with the complex hydrocarbon aerosols in the atmosphere and have formed some sort of "crustal" formation on the surface. I am still working this theory out and should have a more detailed response soon.

Surface winds on Titan are extremely weak. What is seen in the Huygens photo's are typically what would be seen from fluid flows rather than aeolian processes (IMO).

Posted by: dvandorn Dec 6 2005, 07:41 AM

I think your last sentence hits the nail on the head, Jon. Aeolian features on Titan are going to look more like fluvial features to Earth-trained eyes. However, you also note the difference between two different transport mechanisms, one with higher energy than the other -- it would seem to me we're looking at aeolian transport for fines and fluvial transport for pebbles.

Someone posted here that most of the ices present on the surface of Titan, and water ice in particular, would float on top of either liquid methane or liquid ethane. So we *may* be looking at a complex and very non-terrestrial process of crust/liquid interaction.

For as non-terrestrial as these processes must be, they certainly have created some hauntingly familiar-looking landscapes, though...

-the other Doug

Posted by: RNeuhaus Dec 6 2005, 03:29 PM

Rivers On Titan, One Of Saturn's Moons, Resemble Those On Earth

http://www.spacedaily.com/news/saturn-titan-05zo.html

Interesting conclusions:

There are only three parameters that differ significantly between Earth and Titan, Parker said. First is the acceleration due to gravity - on Titan it is about one-seventh the value on Earth. Second is the viscosity of flowing fluid - the viscosity of liquid methane on Titan is about one-fifth that of water on Earth. Third is the submerged specific gravity of sediment - the value on Titan is about two-thirds of that on Earth.

"What this means is that for the same discharge of liquid methane as to water, the channel characteristics on Titan should be remarkably similar to those on Earth," Parker said. "However, because of the smaller acceleration due to gravity, channel slopes on Titan should be wider, deeper and less steep than those on Earth."

"The interaction of sunlight with a hydrocarbon rich atmosphere could possibly precipitate very sticky compounds that could give streams on Titan a degree of cohesion that makes them behave differently," Parker said.

If the underlying physics has been captured correctly, Parker's correlations could be used to predict river features not just on Earth and Titan, but elsewhere as well; revealing the internal consistency of fluvial processes at work under vastly different conditions.

"We are now receiving images from Mars that show relic rivers. But these analogues to what has happened on Earth are very, very old and the processes may not have been very strong," Parker said. "What is happening on Titan, however, may be every bit as active and exciting as what is happening on Earth."


Rodolfo

Posted by: JonClarke Dec 6 2005, 10:53 PM

Legit criticism yes, but much of the carping I have seen reminds me of the type of carping that goes on from the more dodgy fora about the Mars rovers. And I cannot understand how six monthly data releases, over 100 conference abstracts and about a score of major publications can be considered slow.

But we digress!



Would we expect specular reflections under such difuse lighting conditions?



My gut feeling is the same, they look like fluvial tails and it is the most parsimonious explantation. However it would be better to say that measured Titan wind speeds are weak. Can we be sure they are aways weak? Also, given the low density of ice particles, the low gravity, and high atmospheric density, even light winds might be very effective at transport.

Jon

Posted by: JonClarke Dec 6 2005, 11:06 PM

T'other Doug

Certainly possible, but how would we tell?



I don't think so. Liquid methane has a density of 0.42, ice I 0.92, so ice should sink. The difference is not as high as between water and quartz (1.0 and 2.7), but still high. The low density of ice should make it easier for wind to move, especially on Titan.



Indeed! Morphologically it looks more earthlike than Mars.

Jon

Posted by: volcanopele Dec 6 2005, 11:30 PM

1) Based on the work by R. West et al. (2005) (West, R. A.; Brown, M. E.; Salinas, S. V.; Bouchez, A. H.; Roe, H. G. No oceans on Titan from the absence of a near-infrared specular reflection. Nature, Volume 436, Issue 7051, pp. 670-672 (2005).), we should be alboe to see some specular enhancement if liquids were present. since we have thus far been unable to find specular reflection, it appears that at least in the areas observed by ISS, there are no large bodies of liquid. This doesn't rule out smaller bodies of liquid, particularly near the south pole where we have been unable to search for specular reflections.
2) Given that we see enormous features created by wind activity (cat scratch longitudinal dunes) there has to be at least 1 m/sec winds at the surface, likely tidal winds. This was observed by Huygens. You don't need giant gusts to create aeolian features.

Posted by: JonClarke Dec 7 2005, 02:03 AM

I see, I was assuming specular reflections in the Huygens images. I agree with the inference of their lack in the ISS data.



Good point about the dunes. What's the 1 m/s based on? Anyone tried using the dune patterns to map amospheric circulation yet?

Jon

Posted by: The Messenger Dec 7 2005, 05:29 AM

Posted by: BruceMoomaw Dec 7 2005, 07:43 AM

The 1 meter/sec near-surface winds (in a reverse direction from all the winds above 10 km!) are based on Huygens' data -- both the Doppler experiment and the surface images.

Posted by: exoplanet Dec 7 2005, 03:14 PM

"2) Given that we see enormous features created by wind activity (cat scratch longitudinal dunes) there has to be at least 1 m/sec winds at the surface, likely tidal winds. This was observed by Huygens. You don't need giant gusts to create aeolian features."

[/quote]


1 m/sec winds translates to a weak 2.237 mph windspeed here on Earth. On Titan it would feel like a weak 3.58 mph breeze. Can anyone explain how windspeeds this weak can produce such large longitudinal dunes. If the surface winds do not change direction - then this indicates that there is very little to no complex weather patterns (low vs. high pressure systems) so the windspeeds would hardly ever change.

Posted by: AlexBlackwell Dec 7 2005, 06:12 PM

Interesting, Nature didn't go with a Huygens-related cover for the http://www.nature.com/nature/journal/v438/n7069/index.html.

Posted by: Matt Dec 7 2005, 06:37 PM

Titan's lower gravity might aid in the formation of dunes

Posted by: JRehling Dec 7 2005, 07:39 PM

If a given windspeed could move one dust particle, then, the question is, why couldn't it stack a quadrillion? There's going to be a calculus of wind, pressure, gravity, particle mass, particle surface area, particle aerodynamics... Without doing the math, I wouldn't find it any more surprising to see dunes 1 km high than 1 mm. The devil is in the details.

Posted by: AlexBlackwell Dec 7 2005, 08:12 PM

Since I already have access to the journal, I just noticed that Nature is offering http://www.nature.com/nature/focus/huygens/index.html to the Huygens-related articles in the December 8, 2005, issue. I'm not sure if this has been mentioned here today or not.

Posted by: The Messenger Dec 7 2005, 08:19 PM

Are you certain of this, Bruce? The reason I ask is I know that the Doppler team initially reported that from ~70 km down, the winds were strictly from one direction, and they had to change the conclusion when the visual images demonstrated otherwise.

The initial Doppler interpretation was based upon the differential, not VLA triangulation, so there was room for some slop, but to the best of my knowledge they have not reported Doppler data tightly constrained enough to reach this conclusion.

Posted by: dvandorn Dec 7 2005, 09:28 PM

The air is *very* thick at Titan's surface. Pressure is 1.6 Bars and density is somewhere between 7 and ten times the density of the air at sea level on Earth.

The thicker the air, the more friction you have between the air and the surface, so very weak winds have a far greater aeolian force than they do on Earth. That's how a 2.5-mph windspeed (which, due to 1/7th G feels like a whopping 3.6-mph breeze on Titan) can entrain and shift a lot more material than you might think.

Also, the ice "sand" and the organic-smog-particle dark mantling are less dense than equivalent dust and sand particles on Earth. They're lighter, and so more easily moved by winds.

That's how such weak windspeeds can produce such large longitudinal dunes.

-the other Doug

Posted by: helvick Dec 7 2005, 10:04 PM

We biefly mentioned this before but can someone confirm this.

Titan has a predominantly (90%) Nitrogen atmosphere, at similar temperature and pressure to earth it would be similar in density to our air. Standard Density of Nitrogen is 1.25kg/m^3, Density of air is 1.29kg/m^3 at 273K and 1 bar.

Charles law's tells us that Volume/Temp is a constant at constant pressure. Boyles Law says tha pressure*volume are constant at constant temp. They lead to a formula for density given by D=D0 x (T0/T)*(P/P0).

Titan surface temp is ~94K.
Atmospheric density at the surface is ~ 4.35x Earth's.

Other factors (such as "humidity") may come in to play at temperatures this low as this isn't an ideal gas but surely they can't lead to a 2x error.

The air mass above a particular point is probably close to 10x the earths but that's a different thing.

Posted by: dvandorn Dec 7 2005, 10:37 PM

Thanks for doing the math -- I got confused with the whole discussion of that "10 times the density of Earth's atmosphere" line that had been discussed in another thread.

Still, 1.6 Bar and 4.35X Earth's air density lead to a lot more aeolian force than an Earth-based mind would ever expect from weak winds. Enough, I think, when taken with the relatively low density of the drifting particles, to cause the dune structures we've seen.

-the other Doug

Posted by: JonClarke Dec 7 2005, 11:12 PM

While we are on the subject of wind, it is worth noting that longitudinal dunes on earth indicate reversing seasonal wind directions.

Jon

Posted by: helvick Dec 8 2005, 12:26 AM

I agree, just wanted to make sure the numbers were of the right magnitude. A 4.5x density increase is not trivial.

That got me thinking about what would 1 1m/sec wind on titan actually be able to do.
The lifting capability will be proportional to the drag force/density of the lifted material - From the drag formula: 0.5xCdxAxDxV^2 where Cd=Coefficient of drag, A=X-Sectional Area,D=Atmospheric Density,V=Velocity.

The drag increases linearly with atmospheric density and the imparted acceleration increases linearly with the density of the material being lifted, assuming the physical structure of the particles are similar.
If we're assuming various ice type dusts (density ~1000kg/m^3) on titan vs the ~3000kg/m^3 for average stony materials that make up earth dust. Then we have close to 13x the lifting capacity for the same wind velocity.

It's worth noting that since drag is proportional to wind velocity squared a 1m/sec wind on Titan would impart a similar acceleration to its dust particles as a 3.6m/s wind on earth.

Finally the 1/7th g comes into play. That effect is a bit more complicated I reckon but my gut feeling is that for the purposes of dune forming\dust moving it also introduces an additional square root factor ie ~2.6.

It seems reasonable to think therefore that 1m/sec on titan would have a physical effect on ice based dusts (if they exist and are not "sticky") similar to a 9m/sec wind on earth or 34kmh. for those of you who haven't gone metric that's about Force 5 and more than enough to form dunes.

Posted by: BruceMoomaw Dec 8 2005, 02:55 AM

Nope, I was wrong. The graphs of wind speed and direction with altitude have been publicly available for a long time: http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEM23TULWFE_1.html#subhead7
...and there is disagreement between the Doppler and imaging results, although they both show the wind suddenly reversing direction shortly before landing. The Doppler showed this happening about 7 km up, as expected -- but the photos indicated that it happened much lower: about 1 km. I have no idea of the cause of the directional reversal (channeling by topographic features, maybe?)

Posted by: elakdawalla Dec 8 2005, 03:52 AM

I thought I'd try overlaying the DISR wind speed results on the DWE results, and the agreement is really pretty astonishing -- well I guess it's only astonishing if you assume they don't talk to each other, and the DISR and DWE teams are two of the friendliest I know Anyway here's the overlay:



They actually agree near the surface, even though they look different. The reason for that is the DISR graph shows the absolute wind speed (independent of direction) while the DWE graph shows the zonal wind speed. So the DWE graph goes into negative territory close to the surface, while DISR goes back to positive territory (if I'd left the wind direction squiggle on there you'd see it is heading west instead of east). The critical turnaround point at about 8 km altitude is right in the gap between the Green Bank and Parkes telescopes. I sure hope they eventually get some data from the VLBI effort, but the last time I asked Dave Atkinson about that he hadn't seen any results from the other radio telescopes. (He's more curious than we are what the DWE experiment shows at that point.) The DWE data is kind of noisy close to the surface, which could (I am guessing here) be because the winds were variable and/or their speed was of rather similar order to the pendulum motion of Huygens under its parachute?

--Emily

Posted by: BruceMoomaw Dec 8 2005, 12:05 PM

Nice work -- I would never have noticed that.

Posted by: The Messenger Dec 8 2005, 12:35 PM

Good question. I went looking for an answer and found a better one:

Prior to the augmentation of the DWE and DISR results, it was reported that the final hour of the descent was uneventful, especially near the landing. Since the radar loses lock at 150m, this had to be based upon the descent accelerometers and/or the sonic echos.

If you look at the accelerometer charting, it is very smooth:

http://www.nature.com/nature/journal/v438/n7069/fig_tab/nature04347_F4.html

But the sampling rate is quite slow, so minor buffeting could be aliased out. I can't find sonic data, which might give us some indication of the antenna pointing.

Getting back to your question: The DWE angle relative to the Earth was degrading over time, so an increase in noise levels is not surprising. If degradation just prior to landing was due to pendelum effects, the variation in the noise level would drop-off significantly upon landing. Does it? (The graph I have indicates zero noise after landing, but this must be a forced baseline.)

Posted by: JonClarke Dec 9 2005, 02:27 AM

One minor nit to pick. Dust does not form dunes, sand does. Of course dust can aggregate, but in this case the aggregates are equivalent to sand particles.

Jon

Posted by: RNeuhaus Dec 9 2005, 04:02 AM

Huygens Sunk Into Soft Ground

Interesting article, Huygens landed on a relatively soft surface resembling wet clay, lightly packed snow and either wet or dry sand.

Summary - (Dec 5, 2005) When ESA's Huygens probe touched down on the surface of Titan earlier this year, it hit hard, and then slumped sideways into the soft ground. After analyzing the landing in detail, ESA scientists have calculated that Huygens probably hit a surface similar to soft clay, lightly packed snow, or wet or dry sand. It penetrated about 10mm into the ground, and then settled slightly over time by a few millimetres, tilting the probe a few degrees. It's possible that Huygens landed on a Titan beach, shortly after the hydrocarbon ocean tide went out.

http://www.universetoday.com/am/publish/ssp_titan_huygens.html


Below article says that the aeolian force has no influence to the Huygens landing zone except to fluvial force.

Fluvial and marine processes appear most prominent at the Huygens landing site, although aeolian (wind-borne) activity cannot be ruled out. The SSP and HASI impact data are consistent with two plausible interpretations for the soft material: solid, granular material having a very small or zero cohesion, or a surface containing liquid.

In the latter case, the surface might be analogous to a wet sand or a textured tar/wet clay. The ‘sand’ could be made of ice grains from impact or fluvial erosion, wetted by liquid methane. Alternatively it might be a collection of photochemical products and fine-grained ice, making a somewhat sticky ‘tar’.

The uncertainties reflect the exotic nature of the materials comprising the solid surface and possible liquids in this extremely cold (–180 °C) environment.

Strange word

Rodolfo

Posted by: exoplanet Dec 12 2005, 12:36 AM

Okay . . . . Say we have a liquid such as "water" moving at 1 meter per second in one direction over a long period of time. It would seem that the surface would be smoothed rather than ices/particulates forming linear dunes. I used water as a reference due to the higher density of the atmosphere of Titan (water is pretty dense too.....) and it's potential effects. The higher the atmospheric density - there would be a lower probability of extremely large and extensive dunes to occur.

Posted by: BruceMoomaw Dec 12 2005, 08:01 AM

Titan's atmosphere is not even remotely as dense as water -- the difference is about 500 to 1. (To say nothing of the fact that liquid water, being liquid, has tremendously higher viscosity than a gas does.) Extend your current line of reasoning to its conclusion, and you'll conclude that a world with no atmosphere at all will have the tallest dunes.

The question of how fast Titanian winds would have to be to pile up dunes also depends, don't forget, on how fine the accumulated surface organic particles are -- and they at least start out very fine indeed. Are they then glued together into larger clumps by exposure to methane rain? We don't know yet.

Posted by: The Messenger Dec 12 2005, 04:41 PM

Duning is a harmonic wave effect, exactly equal to the wind causing waves, wash boarding of a dirt road, and mogels on a ski hill. If the patterns on Titan are dunes, and not crinkles, the prevailing wind that formed such smooth patterns must blow perpendicular to the dunes, and at a somewhat constant velocity. Anything else would create a great deal of chop - just ask any surfer dude.

Posted by: dvandorn Dec 12 2005, 06:20 PM

Correct me if I'm wrong, but in the various RADAR images I've seen, the long, straight dune-like structures seem to be arrayed mostly (if not invariably) longitudinally. Yes, there is some variation in the north-south axis, which seems to be topographically controlled. But for the most part, these dunes seem to run east-west.

This would fit in nicely with seasonal winds that blow off the poles emerging from their long winter darkness. As temps warm up at the erstwhile winter pole, ices and liquids with a low boiling point flash into gas and rise, pushing air into north-south wind patterns.

Which just happen to blow perpendicular to these major dune formations.

Unfortunately, I don't see that Cassini has a real ability to chart surface wind directions during and through the coming equinox. And, as I understand it, that equinox will occur quite late in any Cassini extended mission (if, indeed, Cassini survives to see it). So I don't know whether or not the resources we have in place are capable of settling the question of how Titan's winds blow as the poles alternate being in continual daylight and continual darkness.

-the other Doug

Posted by: volcanopele Dec 12 2005, 07:51 PM

The dunes we see near in RADAR are almost entirely longitundinal dunes. Unlike most dunes, longitudinaldunes form parallel to the average prevailing wind direction. Their east-west trend is consistent with expected prevailing wind direction in Titan's equatorial regions.

Notice I said average prevailing. Below is a very rough schematic showing cat scratches as they appear in central Belet. In this example, the dunes run from southwest to north east, based on their interaction with the two islands outlined in green. The black arrows just to the lower left of center shows the strength and direction of the winds see in this area. As you can see by the length and boldness of the arrows, the strongest winds come from the west, southwest, and south-southwest, while the weakest winds come from the east and south east. Now that doesn't mean that winds don't come from those directions, but they are generally much weaker than those winds that come out of the southwest.

At the time Huygens landed, winds were come from the east and southeast. Cat scratches in the region run from west to east (note island at upper right in http://photojournal.jpl.nasa.gov/catalog/PIA03569 , which shows you the average prevailing wind direction). So when winds come out of that direction at the surface, they are generally stronger than the winds that coming from the east and southeast direction, which were measured at around 1 m/sec. at the surface.

Posted by: BruceMoomaw Dec 12 2005, 09:39 PM

Well, that's interesting -- it implies that the 1 meter/sec reverse-direction winds Huygens encountered at low altitude really were very limited either in spatial locale or in duration. Again, what a pity they didn't have an anemometer on Huygens (and a precipitation sensor, and a heated GCMS core tube, and a 1-axis tilting mirror for post-landing photos, and...)

Posted by: djellison Dec 12 2005, 10:25 PM

And an RTG, and Wheels, and a mass budget of 1500kg and a $3B budget and Pancam, and........

Given the expected conditions, the mass, volume, data, financial and chronological budgets....I think they did fairly well. The initial mission design really didnt have very long on the surface before dropping the link, so there was little sense in designing anything for any sort of surface duation.

Did Viking tell us everything about Mars? Nope - we have to go back with new questions to ask

Doug

Posted by: volcanopele Dec 12 2005, 10:31 PM

I should point out that in addition to differences in strength, the winds can differ in duration. For example, in the schematic above, winds may blow out of the southwest, west, SSW more often than they blow out of the east and north. Same goes with the Huygens landing site, winds could blow more often out of the NW, W, and SW than out of the east and southeast.

Posted by: JRehling Dec 12 2005, 11:12 PM

To call attention, for a moment, to the Earth analogue, a given location in the Midwest may experience mean winds of about 8 mph from the southwest, but at other times, almost no wind; on rare occasions, 80 mph from the west; on other occasions, 30 mph from the east.

Titan's winds are probably not as violently unpredictable as Earth's, but remember that with Huygens we saw just one place at one time.

Posted by: elakdawalla Dec 12 2005, 11:13 PM

How do you see the speeds and directions of winds change in a specific area? Can ISS see that? Or is this based on atmospheric models?

--Emily

Posted by: exoplanet Dec 13 2005, 03:20 AM

From what I have researched - Titan's temperature is relatively constant from pole to pole (if over 10K difference - please site sources).

I don't believe that Cassini or Earth based telescopes have witnessed meterological high - low pressure systems (where you see on Earth and even Mars substantial wind gradients). Unless there is substantial heating during the day . . I see no mechanisms for wind speed change in either speed or direction at the surface. Would love to hear from someone with an atmospheric science background on this topic please.

Posted by: The Messenger Dec 13 2005, 04:26 AM

I stand puzzled, and corrected:
http://www.physicalgeography.net/fundamentals/10ah.html

As Volcano Pele has posted before, these dunes are dead ringers for the cat scratches. Strong bidirection winds? Does Titan follow any of the rules?

Posted by: JonClarke Dec 14 2005, 05:47 AM

Depends where you are. In some places, central Australia, virtually all the dunes are longitudinal. Other dune types are almost absent. Sief dunes (as their name suggests) are also common in Arabia.

Jon

Posted by: volcanopele Dec 14 2005, 07:42 PM

It's based on tidal wind predictions and our knowledge of how longitundinal dunes form on earth.

Posted by: scalbers Dec 17 2005, 04:51 PM

I suppose I can claim an atmospheric science background, though my study of Titan is rather limited. We do know there are occasional dynamically driven mid-latitude storms on Titan (from ISS cloud patterns), and the polar clouds suggest convective activity occasionally occurs. The Keck long-term imagery also shows the changes in the clouds. Solar energy is weak, so it can take a long time for things to change in the atmosphere. Certainly seasonal changes could potentially alter the winds I would think, as there are seasonal changes in the haze structure. In terms of how surface winds would vary, I would stay tuned to the group at CalTech who presented preliminary findings on WRF (terrestrial atmospheric) model simulations running on TItan at the recent AGU conference. It is taking more than two Titanian years for the model atmosphere to spin up given the weak solar energy. Perhaps these runs will help show the types of variability that can occur, as they have been able to do for Mars.

Posted by: The Messenger Dec 17 2005, 05:40 PM

I will be amazed if they come even close to modeling/predicting the extreme shear winds in the upper atomosphere; the steep Doppler shifts and off-scale accelerometer readings recorded by Huygens.