View Full Version here: : ITN: CO2 Powers Hartley !
11-11-2010, 11:55 AM
Some of the science results of the EPOXI flyby of Hartley 2 are just starting to come out
Primordial dry ice fuels comet jets. (http://www.physorg.com/news/2010-11-primordial-ice-fuels-comet-jets.html)
Of great interest is the comment by Jessica Sunshine[/URL] (deputy principal investigator for the EPOXI mission):
That's big news to me ! Does this also mean that no accurate, (or unambiguous), ground-based measurements for sublimating CO2 exist for any given solar system object??
(I may be reading too much into this statement but is a fairly assertive one ..?..)
Jessica Sunshine (http://deepimpact.umd.edu/science/bios/jsunshine.html) is no slouch in spectroscopy ..
Hmm makes me wonder even more about Earth-based measurements concerning the proportions of frozen CO2/H2O on Mars' poles
Still, it also helps to clarify some lingering questions about the likely composition of comets and their jets.
11-11-2010, 12:16 PM
Hi Craig, wouldn't CO2 in our atmosphere hamper earth based detection?
And maybe the CO2 radiates in the infra red which would be blocked by water vapour in our atmosphere.
11-11-2010, 12:31 PM
I thought this thread was about powering motorbikes with CO2, gobal warming issue :)
11-11-2010, 01:08 PM
11-11-2010, 01:24 PM
Slip of the fingers !!
bit like Malcolm's ..
" thought this thread was about powering motorbikes with CO2, gobal warming issue"
One of those days .. (would've been more interesting if it had been about Harleys runnin' on CO2) !!
11-11-2010, 01:46 PM
I would have thought they'd be compensating for this in the processing of the spectroscopic readings .. which I guess, would give rise to the ambiguity she's referring to.
(I should've also referred to her reference about the space-based scope readings).
I'm more surprised that the space based scopes aren't set up to detect CO2, either! You'd think this would be handy for exoplanet research.
Guess I learn something new everyday !!
11-11-2010, 03:11 PM
NASA are using diffuse reflectance IR fourier transform spectroscopy (DRIFT). Water vapor and CO2 strongly absorb strongly in IR. It's a standard procedure to subtract the effects of water vapour and CO2 for earth based IR spectrometers.
11-11-2010, 04:08 PM
Thanks for that .. very interesting. I'll have to read up more on that one.
Perhaps the compensation by using DRIFT still leaves room for some ambiguity, when looking further out at comets
I should be careful about drawing conclusions about ground based measurements of other CO2 diffusing objects, though. (Like Mars and exoplanet atmospheres).
They also used a gamma ray spectrometer on the Mars Odyssey probe which detected large amounts of Hydrogen ions (from orbit). I believe the conclusion about lots of frozen H2O in the poles, is still inferred from these measurements, however.
PS: I still don't get her comment about the space based scopes, though. :question:
11-11-2010, 05:17 PM
I'm not drawing any conclusions, simply highlighting how one uses an IR spectrometer in the Earth's atmosphere.
One of the advantages of being close to an object is that it allows a specific region of the object to be analysed without having to significantly reduce the aperture of the detector to screen out the surrounding region. This maintains a high S/N ratio.
Clearly Earth and space based telescopes armed with IR detectors don't have this luxury as reducing the aperture of the detector well below the diameter of the exit pupil will block much of the signal.
11-11-2010, 05:35 PM
Hmm .. Thanks again, Steven
I was just snooping around looking for info on DRIFT and I found this one ..
Its a bit of an old article, (ScienceDaily: Dec. 9, 2008), but it is relevant to space bound CO2 detection of an exoplanet..
Hubble Telescope Finds Carbon Dioxide On An Extrasolar Planet (http://www.sciencedaily.com/releases/2008/12/081209144923.htm)
I guess in this case, we've got a hot glowing exoplanet radiating EM/light.
In the case of a comet, I presume it could only reflect light.
Still, I would've thought the absorption spectrum would be evident.
Clearly, the distance to the object vs resolution of the image isn't the problem (63 light-years) !
I'm still stumped !
11-11-2010, 05:46 PM
A little of topic....yes me again....,
Craig you seem to always post great mmm well posts I guess...
I'm amazed that you have amassed over a thousand posts in just 3 ish months!
If I could put a gold star next to your name I would!:P
Sorry ...other than that ... I have nothing to add to this post other than its interesting once again!:thanx:
11-11-2010, 05:55 PM
Thanks kindly for the 'gold star'.
I do kind of consider it to be a bit embarrassing, really .. although, I am trying to contribute as much value as I can (this is probably debatable though). ;)
Most of them are "In the News" posts .. and I'm still relatively new to IIS.
11-11-2010, 05:58 PM
So it is just frozen soda water & dust then.
11-11-2010, 06:02 PM
Yep. It also interesting that they're saying that the sublimating CO2 is what carries the dust off the surface.
Which, I guess, makes sense if its a dirty snowball. (Some people 'round these parts dispute this).
Love to hear from our comet/asteroid hunters .. they know heaps more about all this than me (obviously).
11-11-2010, 06:07 PM
That's because you are dealing with a point source. No need to mask the aperture of the detector. Also you increase the S/N ratio by simply increasing the exposure time.
Isolating a specific region in an extended object is far more challenging in particular when the spectrums of both regions may be similiar. The aperture of the detector may be no larger than a pinhole, in which case lght travelling through the telescope is diffracted at the detector.
The result is a noisy spectrum with a low S/N ratio irrespective of the exposure.
I have had a bit of experience with X-ray spectrometers. You can analyse very small particles in a matrix by using very small detector apertures going down to 0.5mm. The smaller the aperture the noisier the spectrum.
11-11-2010, 06:29 PM
OK. Thanks Steven.
So, the comet passed within 0.12 astronomical units (18,000,000 km) from Earth on October 20, 2010 (8 days before perihelion of 1.05 AU).
The flyby was able to show that the comet nucleus was 2.25 kilometers wide.
So, 2.25 kms wide, (the nucleus), and 18 million kms away.
Could this be considered a 'point source' from Earth ?
(I guess not because of the coma .. although that didn't look very big from the close-ups taken by Deep Impact).
PS: Also interesting is that the jets were coming from the dark side of the nucleus.
11-11-2010, 06:42 PM
You're a great drive for the astro science forum. I actually started reading a lot more of it as have a lot other people I suspect since you got on board. Keep up the good work. Very entertaining and educational. :thumbsup:
11-11-2010, 07:05 PM
Gee .. what's goin' on here ?
Anyway, thanks Marc. Appreciate the feedback.
Last time we saw you here, you were chasing Mr Pressure !
Come to think of it, I wonder what happened to 'the mighty Pen' ?
11-11-2010, 09:31 PM
Getting back to your original question as to why Hubble has detected CO2 on a distant planet, I should have also added that the IR spectrum of CO2 can be measured because it exists as a gas. The temperature is high enough for CO2 molecules to stretch, bend and vibrate which allows the gas to absorb IR radiation.
When CO2 exists as dry ice in temperatures approaching absolute zero, the molecular motions largely cease and IR is not absorbed.
The IR spectra of CO2 is measured at the jets because there is sufficient thermal energy for absorption to occur.
If an Earth bound or space telescope is unable to resolve the jets then the spectrum of CO2 would not be detected, it would be lost in the solar IR reflected off the comet.
If on the other hand the telescopes can resolve the features, I am now inclined to think that you don't have to reduce the aperture of the detector, the surrounding features are still in ice which might not interfere with the spectrum of the jets.:shrug:
11-11-2010, 09:33 PM
Perhaps Mr Pressure was deflated by the experience.
I don't think he liked my "mighty pen" remark.
12-11-2010, 07:53 AM
Yeah .. the Pressure is getting to me on this thread !
Seems to be a good idea to wait for the paper on all this.
Its probably too early to expect one from Ms Sunshine.
Its all very interesting though. The jet action over a long period of time would also effect the orbit. Its interesting that the jets are coming from the dark side rather than the sunlit side, too. (It rotates over an 18 hour period).
Thanks everyone for being involved in this thread.
I've actually enjoyed it !
Plenty to learn about when it comes to comets !
12-11-2010, 10:42 AM
The findings haven't quite confirmed exactly what is happening but it does vindicate the models of ice sublimation by comets.
There still is a lot of unanswered questions though, it's only a matter of time until we do get to know.
Im stoked with the images and the findings and am wanting always to learn more, it'll be interesting to see what else is being found!
12-11-2010, 11:05 AM
It also vindicates the prediction that water ice is not the main driver of cometary jets. ;)
12-11-2010, 11:10 AM
On man .. just when I was having fun ..
PS: No plasma visible in the photos, either !! ;):)
12-11-2010, 11:40 AM
I wonder if Ms Sunshine has interests in Solar astronomy.:P
12-11-2010, 11:45 AM
Well .. I mean .. there's the missing link right there !!
The Plasma Queen of comet watching !!
12-11-2010, 01:03 PM
Nah... some of these guys sound scary to me. :atom::nerd:
12-11-2010, 01:33 PM
Emily has a point there ;) they ignored her 'nightside' 'jets' question too. Kudos to Emily for seeing a 'rock'. heheh
It'll be nice when these theorists define the words they are using!!! grrr
12-11-2010, 01:43 PM
Ahhh Alex, matey (er .. .brother)
If they did that, there'd be no more mysteries
. and mysteries is what gives life some substance
something we all share in common!.. ??
12-11-2010, 01:54 PM
hah. what an easy job aye...
12-11-2010, 02:18 PM
Emily didn't see 'a rock'. She said 'bouldery' and Jessica used the term 'clumps'. Wouldn't you say it looked like a conglomeration of something smooth (obviously there's solid CO2 there somewhere) and some rough looking bits. No one said anything about 'rock'.
I mean, there is dust carried off by the CO2 jets. There also H2O coming off it too. Its mass is pretty low, (just like others). If it was consolidated rock, it'd be heavy, wouldn't it ? Maybe some 'stones' in there, but no big consolidated rock.
Also, it seems the jets also come off the lit side. (Not exclusively the dark side). The reports of the dark side jets are because that was a surprise. This doesn't mean that there's only dark side jets.
12-11-2010, 03:03 PM
We need to be careful of assumptions.
Yes i am with emily, it looks bouldery... and since most things bouldery are rock i'm ok with 'rock'. So on this point i might disagree with Sunshine, and i don't know what Emily means by Bouldery, so i'm going to have to go with the english definition "bouldery - abounding in rocks or stones"
Jessica will need to define 'clumps', before i can pay attention to her there.?!? she said she honestly can't say what 'clumpy' means?
So i am left confused.
Yes, there are competing theories as to 'how' this is carried off. MS = internal jets dragging. EU = electro sputtering (similar process to cover scope mirrors). So we don't have any firm basis to exclude rock here.
Careful now. There is H20 spectra around the nucleus. MS says there is partial water ice from the jets. EU says it's OH radical forming electrically from solar wind interaction with O from nucleus, not from a jet. The distinct lack of surface ice supports EU here. Again we cannot rule out rock. MS has invoked subsurface hidden ice.
Here we could be leaning towards that, but we cannot exclude the possibility of a geode. But yes mass is an interesting one, i'd like to explore this more. i dunno.
ofcourse there are sunside jets, dark-side jets, and particularly interesting are these photographed 'ridge of jets' see 20:05. Plasma discharge particularly follows like this, and has been written about by both Peratt and Thornhill.
What could we expect from mainstream hypothesis regarding the ridge of jets? (bearing in mind, this is a 1mile ridge!!)....
Possibly a sub-surface trench of ice? hmmm seems unlikely? It would have to be a pre-existing subsurface condition yeah? thats the only explanation for sub-surface sublimation no?
Fascinating pictures... I'm again struggling to see dirty snowballs here, or to figure out what causes a 1 mile row of jets. What happens if that 'row' moves... and tracks across the surface.... (not that it has).... wouldn't that be a difference we could look out for? i wonder.
12-11-2010, 03:18 PM
Isn't 'the row' just an illusion from the angle of viewing ?
Methinks its discharges from all over it !
I'll have to have another look.
And they have spectrographic evidence !
Sorry Alex .. I think the following is a quantum leap .. (even for you):
Where's the evidence for that one ?
Even according to ya mate Peratt, there'd be some kind of spectroscopic data left behind if it was a plasma discharge !! Jessica is a guru on this and she didn't mention any remarkable plasma discharges !!
12-11-2010, 03:34 PM
Watch the video and explanation again Craig. It's clearly described by Sunshine, as a ridge of jets. Judging from the attached scale indicator, i read the linear ridge of individual jets to be 1mile long.
It is clear that there is a preferred geometry for these emissions that relate to either surface features (as pointed out by that other old dude)... (and is probably required by standard-sublimation)..... or the linearly arranged emissions relate to something else. Since this is way less than the 18hrs of rotation, we wont know if the emissions move in a line (indicating a highly electrical interaction), or if the jets are fixed in existence during their thermal cycle (you would think this is required by a sub-straum sublimation theory).
From these images we do not have a definitive answer, although some creative explanations for linearly arranged jets are required for subsurface sublimation. I can only think of some form of sub-surface structure... it all seems highly unlikely... i dunno... i await these ideas.
I will again find the edm papers. It is not a jump to suggest plasma discharges in cylindrical rows, this is exactly the morphology of auroral discharge, and exactly what we find in laboratory experiments, hence another expected feature of electric discharge.
Plasma exists in dark mode, glow mode and arc mode discharge. So it does not necessarily mean it will always produce what i think you are searching for.
As an example, for perspective, these photos were taken looking through a plasma (the solar wind).
The key difference between the comet models here are electro-dominant-emission-processes, vs thermal-jet-driven-processes.
It is very clear.
12-11-2010, 03:44 PM
Ok .. so here's the released spectrograph results (http://epoxi.umd.edu/3gallery/CarbonDioxide.shtml) (albeit a bit crude . and dumbed down ..)
but even if your plasma was in dark mode, there'd have to be be some kind of reasonably large spectral signature in the 2 to 5 micron region to account for the jet activity. Plasma isn't invisible across the bands these guys were looking over. If it was close to flipping into the glow mode then it would be emblazened across the whole thing (same for arc mode). It would have to be in the dark mode and there'd still be some kind of signature
They say there's organics: methanol, etc. but nothing else.
PS: I haven't had a chance to look over the footage again about the line of jets .. standby. Cheers
13-11-2010, 09:23 AM
The spectrum completely and utterly refutes a plasma discharge mechanism.
Apart from the obvious hydroxyl and carbonyl peaks corresponding to water and CO2 respectively, the spectrum is an absorption spectrum.
A plasma discharge will produce a continuous emission spectrum across the IR range.
13-11-2010, 10:45 AM
Yes. After I wrote my last response to Alex, I was thinking I didn't express where I was coming from very clearly.
I've been trying to chase a few things up since I wrote it ..
I'm not sure whether there'd be any effect on an absorption spectrum being taken of the escaping gases, (taken simultaneously), as this hypothesised, sustained 'dark mode' build up was occurring. (Ie: if it even was occurring at all).
If both were happening, presumably, the gases would be getting hotter and the ionisation levels would be greater, so I'd guess we might see more ionised compounds in the absorption bands (?)
As far as emission spectra are concerned, presumably this could only be visible if the energy levels were great enough to either move any ionised gases into the 'glow' or 'arc' regions (beyond 'dark' mode).
But the thing that also doesn't add up in Alex's hypothesis, is that there would have to be either of these active, visible discharge mechanisms happening, in order to generate the forces necessary to create the visible, collimated structure of jets.
And what the scientists have determined (from the absorption spectra) is a definitive conclusion that they are just plain CO2 gas jets !
13-11-2010, 11:54 AM
How can you make the conclusion that the gases are emitted from the subsurface, as opposed to the hypothesis that the O-(from comet) and H+ (solar wind) combine to form hydroxl in the near atmosphere?
This would provide for absorption spectra.
Emission spectra from surface activity would be so localized and spiratic, i do not see these images having the resolution to determine this, the majority of the spectra would of-course be the absorption, this has always been the hypothesis of the electric comet.
Anyways... any ideas on the ridge of jets craig/steven? I'm very puzzled as to that feature, and how a sub-surface sublimation model can produce that? must be a pre existing subsurface structure... puzzling?!? enlighten me.
13-11-2010, 12:28 PM
Man, I feel for ya (just a little bit ;))
You choose an extraordinarily difficult path when you reject or ignore anything coming from anyone who actually has the data in front of them.
In this case, they've stated publically, that they don't even have the full set of data downloaded, yet (120K photos).
This kind of forces you into a corner, which then forces you into having to come up with an answer, before anyone else has even examined the data (let alone, asked the relevant questions) !!
Honestly anything that comes up in this conversation will be purely conjecture, supposition and my 'belief' vs your 'belief'!
Why don't we wait until they've published their findings and then discuss it ?
Who knows why there might be a ridge of jets ?? I'm not even sure there is, let alone what might have formed it !!! I don't have access to detailed scientific value photos and I doubt whether you do either (??).
(Nothing personal or anything .. I'm just sayin' … )
PS: Can you define "electrical sputtering" ??? What does that mean ??
13-11-2010, 01:11 PM
To add further to the what you have stated Craig.
Absorption occurs when the energy of the absorbing photons from the Sun, is not large enough to push electrons in the atoms of CO2 or water into higher energy states. Instead the energy impacts on vibration or bending of the molecular bonds.
For example the O-H and C=O bonds in water and CO2 respectively vibrate and have a specific resonance frequency. IR photons of the same frequency can be absorbed as a result.
The mechanism for emission in this circumstance is completely different. The charged particles in the plasma are producing a continuous emission spectrum.
Suppose we try to combine the two and claim the water and CO2 are effected by radiation emitted from the plasma. That doesn't work either. The higher energy photons absorbed will shift the reasonance frequency or destroy the bonds through ionization.
You will not observe the absorption spectrum given by NASA.
13-11-2010, 01:20 PM
This is *not* the hypothesis of the EC.
The hypothesis is that the OH and CO form from interaction with the solar wind.
Absorption spectrum of-course still applies.
13-11-2010, 01:24 PM
There was a NASA press conference, where Dr Sunshine said there was a ridge of jets. She shows a photo of the ridge, and calls em a ridge?
I dunno, i guess i'm trying to find if *any* model inclusive of EC has an explanation for this ridge (EC naturally expects emissions from raise points)?
Since from my eyes and ears, i'm convinced there is a ridge, as presented by NASA. Why else would they dedicate a portion of the press conference to the feature?
Yes of course i will wait to see what their conjecture is, it just seems a very interesting surface feature, it could form a testable one.
The Electric Comet is just an extension of this process, using the elongated orbits of the rocks and the process of charge equalization as the object moves in differing regions of electrical potential. The sputtering process excavates material and combining with the H+ solar wind forms what we *think* is H20 breaking down... instead it's OH forming. It's a rather simple picture, vastly differing to the prevailing paradigm.
13-11-2010, 01:27 PM
That is totally incorrect. The hydroxyl you describe is a hydroxyl radical.
The hydroxyl radical is observed at far infrared at 119 microns. The hydroxyl in the NASA spectrum is at located at 2.7 microns. It is an example of an associated hydroxyl, in this case associated with water.
13-11-2010, 01:31 PM
It wasn't mean't to be an EC hypothesis.
The NASA spectrum completely destroys the EC hypothesis , unless you want to rewrite the science of spectroscopy.
13-11-2010, 01:56 PM
You seem to have shifted in your theory from post #34:
to post #41:
but .. hey
who's counting ??
I'd treat the verbage in the press conference as anecdotal until they write a paper. In science, its not until you write a paper that you can prune out human illogical errors ! By the way, how's your Pulsar Relaxation Oscillator paper coming along ? Bojan & I are interested in the section on oscillation precision !
13-11-2010, 02:10 PM
This absorption spectrum and emission spectrum stuff is very interesting.
I was reading up in Wiki (its Ok 'cause Alex now uses it to explain 'sputtering' ;) ), about infrared spectroscopy (http://en.wikipedia.org/wiki/Infrared_spectroscopy#Number_of_vib rational_modes).
Just looking at the cool animated models on the wiki page makes me realise just how complex it really is.
There is a relationship between emission and absorption spectra, huh ?
For others reading this post, I find this quote (http://en.wikipedia.org/wiki/Absorption_spectroscopy#Relation_to _transmission_spectrum) to be very cool:
13-11-2010, 02:12 PM
Sorry here i meant, emission of material (sputtering) of the O negative to combine with the H+ of the solar wind.
Sorry if i confused with 'emission' as in spectra, with emission of material. I might use ejection or sputtering hereon.
I'm not sure if the spectro has the resolution to perform on the near-surface hotspots? Steve would you know?
Steven has raised a spectro-question i will need to seek clarification on, i welcome this.
* Steven is it fair to say that 2.7micro is exclusively water associated hydroxyl?
Just wanted something you felt 'safe' with ;)... although yes it is often dangerous to use.
13-11-2010, 02:18 PM
13-11-2010, 02:32 PM
From The HRI site (http://deepimpact.umd.edu/tech/hri.html) for Deep Impact spacecraft …
For the Hartley 2 flyby:
Pretty neat. And should be good enough to pick up near surface hotspots.
I'm not sure if we've seen the best hi-res photos or not, yet.
13-11-2010, 02:33 PM
The relationship between absorption and emission can be described by the following steps.
(1) Atom or molecule absorbs photons.
(2) Electrons are pushed into higher energy levels. Atom or molecule is in "excited state".
(3) Electrons move back to original energy levels, atom or molecule moves back to unexcited or ground state.
(4) Photons are emitted during return to ground state.
13-11-2010, 02:47 PM
The region 2.7-3.0 microns is the "stretching vibration" for the OH group for a variety of molecules not only water but alcohols, organic acids, phenols etc.
There is another region at 7.0-8.0 microns which is the "bending vibration".
Unfortunately the radical or free OH is way off the scale at 119 microns.
13-11-2010, 02:52 PM
Thanks Steven. Your explanation (for the absorption/emission relationship) makes it (deceptively) simple.
back to my original quest to fin out why Infrared Spectroscopy of Comets from Earth/Orbital platforms "doesn't work" (Ms Sunshine's words)
I found a great paper (http://arxiv.org/pdf/1010.1171v1) on this (Dated 6th Oct 2010, 10.MB), and it seems the dust emanating from these beasties causes polarisation of light in different parts of the absorption spectra. This seems to cause all sorts of problems for which they've developed corrective measures (theoretically based).
There's a lot more issues/material to read up on in order to understand Jessica's comment. No great surprise (to those of us who accept our lack of knowledge for not understanding things .. ;) )
I'm getting cheeky .. time to go and enjoy the beautiful weather !
Cheers, Rgds & thanks to all for your time/explanations.
13-11-2010, 03:00 PM
I'll have a look at the paper mainly because Victoria is under water.:)
13-11-2010, 04:28 PM
Its interesting that WISE and Hubble took images in preparation/support for the EPOXI/Deep Impact encounter.
It seems that Hubble is optimised for shorter (almost UV) wavelengths - I'm not sure about WISE.
I don't think either can see around 119 microns.
13-11-2010, 06:13 PM
Here is some interesting facts on IR astronomy.
I was intending to take CCD images through IR blocking filters and IR pass filters. Subtract the IR blocked images from the IR pass filters to produce an IR image.
Not so after reading the facts.:)
13-11-2010, 06:54 PM
The link you provided says:
Oh well .. there goes that idea, eh ?
Just correcting my previous post about Hubble:
Hubble had Near Infrared Camera and Multi-Object Spectrometer (NICMOS): 0.8 to 2.4 microns
which was superseded by: Wide Field Camera 3 (WFC3):0.8 to 1.7 micron.
Also take a look at the difference (http://en.wikipedia.org/wiki/Wide_Field_Camera_3) between WFC2 and WFC3 !!
I guess Spitzer and WISE, (then eventually the Webb), are the preferred infrared platforms now, huh ?
13-11-2010, 07:20 PM
Thanks Steven, very helpful explanations. Appreciated.
13-11-2010, 07:21 PM
This is quite interesting. What did Hubble use to detect CO2 on that distant planet 63 light years away?
The Carbonyl group has an absorption peak at 4.3 microns out of range of the listed detectors.
13-11-2010, 07:28 PM
hmmm... spectro Rabbit holes...
Steven can you recommend a good text on spectro? I'm intrigued.
13-11-2010, 07:41 PM
NICMOS ! It seems !!
14-11-2010, 07:23 AM
Ok. So it seems that I may have used a poor example of exoplanet atmosphere detection using Hubble's Infrared NICMOS. (There aren't that many to choose from at the moment and the technique is evolving …).
It seems that since the announcement of HD 189733b's atmosphere detection in post #15 and referred to in my post below, there has been controversy over the measurement technique.
Swain has produced several papers on it all. The most up to date ones are:
A ground-based near-infrared emission spectrum of the exoplanet HD 189733b (http://arxiv.org/pdf/1002.2453v1) (submitted 12 Feb 2010):
They went on to say they used the SpeX instrument on the NASA Infrared Telescope Facility (IRTF)..
The SpeX instrument was configured to observe between 1.9– 4.2 μm at an average spectral resolution of 470. (!!!!)
Then someone challenged the measurement technique….
14-11-2010, 07:37 AM
Ok .. so then Swain defended and refuted the challenge (sounds familiar ??):
(http://arxiv.org/pdf/1011.0476v1) (submitted October 20, 2010):
Gibson hasn't yet responded.
So, apologies for any confusion resulting from use of this example.
It seems that both ground-based and space based IR Spectroscopy is evolving rapidly as they work out which IR bands they're interested in, (due to molecular behaviours), as the sensing technology becomes more precise and models evolve.
This should not make much difference to the Hartley measurements though. I'm starting to see how Ms Sunshine's comments make sense and why they sent the probe to do the close-up measurements.
14-11-2010, 08:21 AM
Just for the record, the original paper where Swain announced the detection of H2O, CO and CO2 is here (http://arxiv.org/pdf/0812.1844v2). Dated Dec 10, 2008)...
Note that this paper was submitted on 10th Dec 2008. It seems that there was a lot of modelling done before making the announcement.
He has subsequently defended it and re-inforced his original findings using the ground based measurements in the 1.9– 4.2 μm region (as my last two posts).
A case where initial theoretical models have been vindicated and where rigorous peer-review challenges have improved the credibility. Good stuff !!
14-11-2010, 10:00 AM
There is a lot of information on the Internet for general spectroscopy.
For IR spectroscopy this might be useful.
14-11-2010, 10:02 AM
Very interesting information you have uncovered Craig.
14-11-2010, 10:20 AM
The bit that's still got me is the IRTF ground based facility (http://en.wikipedia.org/wiki/NASA_Infrared_Telescope_Facility). From Wiki:
All done from Mauna Kea !!
They also use fairly extensive adaptive optics there as well.
Haven't looked at ESO's facilities yet.
19-11-2010, 07:21 AM
In the News this morning .. they've now released the High Resolution Camera images. (http://epoxi.umd.edu/index.shtml)
They clearly show H2O ice particles emanating from the surface !!
Also, here ya go Alex
the absorption spectrum overlaid (http://epoxi.umd.edu/3gallery/20101118_Sunshine2.shtml) with lab test results showing the particle size (~ 1 micron).
And the main press release is here (http://epoxi.umd.edu/7press/news/20101118.shtml). A few notable quotes:
Water, water everywhere
powered by CO2 jets in certain parts
the interesting image is the dust image. It seems to be fairly well contained around the nucleus (when compared with the visible, CO2 & H2O images. (http://epoxi.umd.edu/3gallery/20101118_Sunshine3.shtml)
No mention of rocks anywhere ...
Fascinating stuff !
19-11-2010, 09:12 AM
Good old NASA news releases aye... heheh
Mike A'hearn: "Those are all chunks of ice.... size of a golf ball, size of a basketball"
Dr Sunshine: "While they appear to quite large, they are actually quite small.... we are *not* seeing hail sized golf balls.... they are more of a dandelion puff, the width of a human hair."
what the? that's a pretty big contradiction?
These bright focal *spots* (not eventually visible columns) on the night side on the nucleus are amazing, wonder why they decided to specifically not cover that feature? Given Emily specifically asked in Q&A1... and was cut off in Q&A2?
Mike A'hearn: "We know that ice is between a few inches and a couple of feet below the surface, we know that because we saw that, we excavated it with temple 1"
Sorry, but didn't slamming that projectile into Temple1 make *no change* the to associated-hydroxyl (h20) spectrum?
Also... wasn't surface photographs of Temple1 99.975% *not ice*? (see my other iis thread for those specifics)
I sense a bit of reification here... hmmm
2 different types of comets in 1 aye... hmmm... each comet is different? The model is now way way way more complex, as Ahearn said. Also notice Ahearn touched on the resolution of the spectrometer, saying the resolution of their onboard is pretty poor... said "keck" is better???... so i don't see your desire of actual surface points arc-ing spectro's being possible with this test.
PS: Whats up with the Q&A sessions and people calling in? always get cut outs etc...
PPS: for those interested in the news conference, http://www.youtube.com/watch?v=j0x-j1D4oJE
19-11-2010, 10:21 AM
5:50 - "we think"
possibly up to the size of a basketball probably very porous.
Less than 1 micron .. fluffy aggregates .. (this is from the spectrograph measurements taken from inside the coma). These measurements have an overlay of lab compared particle sizes displayed on the same graph. The graph measurements are clearly more accurate, as they give this size comparison. Ahearn was speculating about particles further out from the immediate surface coma based on optical (longer range, wider angle) photos.
They are saying that there's a completely varying distribution of object sizes (Depending on how far out you look). Pretty reasonable summary from looking at the wider field images. Ice sticks together too, so somewhere further out, you'd expect there'd be more snowball sized blobs.
when you consider the words which clearly denote speculation (as declared by Ahearn, himself), at this stage of the analysis. Sunshine is basing her statements on the spectrograph readings .. ie: closer range, tighter field of view, higher resolution, thus .. more accurate.
A conspiracy !!
Don't know about Temple 1 .. I'll leave comments up to others, but it seems to me that you're reading a lot of what you want to hear into what they're actually saying.
Hartley 2 has more frozen CO2 as evidenced from the spectro measurements, which clearly show lots of CO2. This is what differentiates it from Temple 1.
Clearly the onboard (1 to 5 microns) spectro doesn't have to be as sensitive (resolution) as Keck's. After all, Keck is a lot further away and works in higher bandwidths.
Can you clarify your last question (following the 'dots') ? I'm not sure what you're asking .. I don't have any desires about surface arcs !!! This would be an emission spectrum which would turn up across all bands measured. Its absent in the measured spectro results !! .. So .. no arcs !!
Yeah .. the cut-outs are a bit frustrating !! Why wasn't your mate Emily present at the conference, I ask ???
19-11-2010, 10:26 AM
Shes not my Mate, shes Phil Plait's mate, who is your mate?
this is getting weird
19-11-2010, 10:29 AM
Apologies … thought you liked her questions ..
Lets get back to spectrographs and comet data ..
19-11-2010, 11:15 AM
Where i am stuck in sincerely trying to compare the models, (not that anyone else has to)... is how to isolate these hydroxyl's from all the other possibilities of formation.
IE, can the assumptions be questioned, does there exist laboratory physics (ie solar wind with charged body) that may determine associated-OH formation processes 'other than'.
Now you might say "i'm just looking for something"... but i'm actually "looking for" a solidly falsifying test, of either model on these spectro's.
I hope this makes sense.
19-11-2010, 12:44 PM
I'm no particular expert in all this, but I guess all sorts of OH bonds can form in all sorts of places for all sorts of reasons.
The question is: is there anything special about a comet coma that would cause this to happen ?
Firstly, the elements have to be present (in some kind of state) and then something has to force the molecules to bond with eachother ie: temperature/energy or chemical.
In this case, comets come with H2O already formed. So we don't have to worry about the creation of the molecules.
19-11-2010, 01:04 PM
Craig, spot on. H20 is assumed to be sub-surface (under several inches, to feet of dust), we do not *know* this, it is an assumption.
You are describing the hypothesis of the electric comet, and the temperature/energy/chemical requirements of 'sputtering' and 'formation'.... this is the gist of the hypothesis.
Either way this OH spectro does appear to be an all exclusive test, as these associated hydroxyl bonds occur with formation processes... hmmm
Yep, but this assumption swings both ways, sublimation theory will need to explain how some molecules remain there, if not 'formed' etc.
19-11-2010, 06:22 PM
Ahearn also mentioned the volumes of escaping gases. This is how they're predicting the eventual complete evaporation/sublimation of the comet to be ~100 years.
Any other 'hypothesis' would have to account for the formation of this volume of gas from some form of base elements (masses and composition) and electric discharge. It's a bit difficult to see this coming from discharges interacting with ordinary rock !
Also, given how close the probe came ~450 miles, I would've thought the electric discharge/sputtering would've been easily detectable from the onboard radio receivers. (Probably as broad spectrum radio interference). Same should have happened at the Temple 1 encounter.
No mention of any radio interference with comms etc, either.
19-11-2010, 06:55 PM
Yeah good points, i want to investigate how they determine the volume. If this is because the cloud 'exists', the cloud size x "jet" size *needs* to require a certain amount of ejection. I guess i'm trying to say can we isolate the measurement from the assumptions or requirements of those assumptions.
I dunno. Again i'm intrigued.
1) 450 miles was not predicted to be close enough for discharge. I would not assume it would be. I'd say the Rosetta lander will be designed in a way to reduce conduction dangers (carbon fibre).
2) Temple 1 *did* include a *pre-impact* flash. This was a *pre*diction of the electric comet. Along with the blinding flash. (also covered in my other thread).
PS: (This is the knowledge Vs understanding process i was speaking about in the math thread)
19-11-2010, 07:42 PM
The volume, I think, has been calculated from observations of the particles in jets (times the numbers of jets, luminosity/density, etc, etc).
Also, I'm talking about Electromagnetic Radio Interference (RFI) being detected by onboard radio systems, emanating from the 'sputtering' that your discharge model is hypothesising. (As distinct from a direct discharge between the approaching spacecraft and the comet nucleus).
They did cover the whiteness which you refer to as a 'flash' in today's conference - optical effects from particles forward scattering light and backlit effects. If a discharge, then RFI would've been all over the transmission bands .. come to think of it, this probably would've slowed the transmission of the photo data/science data as well .. no mention of this, either.
19-11-2010, 07:55 PM
if there was an electrostatic field surrounding the comet (due to hypothesised discharges), I would've thought that the spacecraft would become electrostatically charged also. (??)
The dust they spoke of would've stuck all over the whole spacecraft .. ever polished ya car and driven through bulldust ??
That'd have all sorts of attitudinal issues on the spacecraft, also, (not to mention gunk on the camera lenses ;) )
I think they said they only had about half a dozen or so possible 'impacts' in the conference. A build up of dust would effect the spacecraft in a different way to impacts.
19-11-2010, 11:14 PM
Craig, go look at the temple1 data/photos it was not a flash. It was a FLASH! It totally blinded (saturated) the cameras way way beyond expectations. Links are available in my other thread, i think it was called Dirty Snowballs V Plasma comets or something...
(I think you are referring to the 'brightpoints' here, this is not the 'flash' i mentioned)
Is this just conjecture? Is this a strawman?, or are you basing this on something solid i can investigate?
19-11-2010, 11:17 PM
Good ideas, comets are indeed surrounded both surface and expelled in ultra fine dust. This is another natural expectation of electro processes (the same as we use to coat out telescope mirrors).
As far as the passing spacecraft being close enough, electrically i think not. Remember this is a camera taking a photo of something 'over there'.
Rosetta on the other hand may just resolve alot of these questions.
21-11-2010, 12:13 PM
OK. So I've been doing a bit of reading on this front.
Here we go
Deep Impact Instruments (http://www.springerlink.com/content/r2h12x38p52h8306/fulltext.pdf) (2MB).
Section 5.3.6. IR Spectrometer Alignment, Wavelength Map and Spectral Resolution, Figure 27 (Page 90/91):
Spectral resolving power is a measure of the ability of an instrument to resolve features in the electromagnetic spectrum. It is usually defined by:
where Δλ is the smallest difference in wavelengths that can be distinguished, at a wavelength of λ.
For comparative purposes, the Hubble "Space Telescope Imaging Spectrograph" (STIS) can distinguish features 0.17 nm apart at a wavelength of 1000 nm, giving it a resolving power of about 5,900. An example of a high resolution spectrograph is the Cryogenic High-Resolution IR Echelle Spectrograph (CRIRES) installed at ESO's Very Large Telescope, which has a spectral resolution of up to 100,000.
The graph shows the measured test results of the Spectral Imaging Module (SIM), which has a design bandwidth for detection from 1.05 to 4.8 micrometres. At the top end of 4.8 microns, its resolving power is about 400 which is around the mid point of its resolving range.
So, clearly there are more accurate detectors around but this beastie was designed specifically to fit on a spacecraft AND specifically to examine the nucleuii of comets at close range.
Ahearn's statement is valid ... as is the accuracy of the onboard technology (ie: it is certainly fit-for-purpose to detect H2O, CO2 and organic chemicals in their native modes).
So my only question now is, what emission spectral lines, (of typical, expected ie: 'known' comet compounds), might one expect to find in this band if electrically induced emissions were occurring ?
And are they present ?
21-11-2010, 12:40 PM
Ok. So now I've found another relevant, (to spectra discussions), paper published 14th Jun 2010:
Detection of parent H2O and CO2 molecules in the 2.55 μm spectrum of comet C/2007 N3 (Lulin) observed with AKARI (http://arxiv.org/pdf/1006.2640v1) (700kB).
The spectrum is on page 14 and it is interesting to compare it with Hartley's (over, roughly the same, 2.5 to 5 micron band). Nowhere near as much CO2 as Hartley 2 .. a little more H2O though, and similar hydrocarbons (incl CO v(10) at 4.67 μm, organics at 3.23.6 μm) .. similar, but different to Hartley 2. They talk about a combination of CO, CO2, and dust thermal emissions at 4.5 μm, H2O 'emission' region of 2.72.8 μm.
I'm unclear as to whether they actually mean emission or absorption lines. (???).
The paper is an interesting read as it talks about up-to-date near-infrared and infrared detection limitations as well as about the spectra lines and their causes.
21-11-2010, 01:28 PM
IR is low energy. What you see are absorption lines. There is not enough energy to excite electrons into higher energy levels resulting in emission lines when the electrons return to the ground state.
As you decrease the wavelength of the radiation, the energy increases.
Visible and UV radiation will push electrons into higher energy levels. X-rays can remove electrons completely from a chemical bond resulting in ionization, gamma rays are the mother of all photons, apart from completely stripping an atom of it's electrons they can destroy the nucleus.
21-11-2010, 02:04 PM
These guys seem to be fairly loose in their use of the term 'emission lines'
(thanks for clarifying).
If I'm reading these papers correctly, it also seems that as a comet nucleus approaches the Sun, molecules can be excited to the extent that they can still exhibit lines in a fairly narrow band of the IR spectrum ?
Presumably, this is due to external (solar induced) UV excitation.
21-11-2010, 07:08 PM
This is a translated document and one of the better ones.
From experience many translated Japanese scientific and engineering documents end up in incomprehensible Jinglish.:(
21-11-2010, 07:25 PM
Err …. Ok .. I didn't realise that when I read it .. sorry about that.
The more interesting one is:
Previously unobserved water lines detected in the post-impact spectrum (http://arxiv.org/abs/astro-ph/0610673v1) by R.J Baber et al University College London (Oct 2006).
In this one, they talk about 'Solar Pumped Flourescent' (SPF) transitions of H2O following the Tempel 1 impact. (SPFs are apparently transitions from doubly-excited stretch states).
The spectrum centred on the range 2.894 ±0.040 μm. They also talk about measuring secondary peaks shortly after impacts, which they attribute to Solar or Stochastic Heating (SH), (apparently states with 'three or four quanta of vibrational excitation'), although the actual mechanism that created these is still not fully understood, yet. (I think).
Interesting paper (and written in English).
21-11-2010, 08:55 PM
Thanks for this info Craig. Cheers
21-11-2010, 09:04 PM
I should have read the Japanese translated paper more carefully instead of assuming that translation errors occurred.
Their use of the term emission is quite correct.
When a molecule absorbs IR, the molecule is in an excited state. However when the molecule returns to the ground state thermal energy is released. Hence an absorption spectrum is observed.
For higher energy photons, the return to ground state emits photons hence an emission spectrum is observed.
Molecules also absorb thermal energy. In this case when the molecule returns to ground state IR is emitted.
The wavelength of the IR radiation emitted is a function of the amount of thermal energy absorbed.
So when CO2 and H2O are boiled off, thermal energy has been absorbed and IR is emitted.
The same principle applies to colliding objects into comets. Part of the impact energy is converted into thermal energy which excites the molecules and IR is emitted.
Hope this clarifies things.
22-11-2010, 08:14 AM
Many thanks for that explanation. I'm going way back into my dim, dark education here, but I do recall what you say .. must've actually learnt it somewhere !
Very interesting. A further question … when energy disturbs a body of gas in thermal equilibrium, would both emission and absorption spectra be observed to be occurring simultaneously ? (I'd guess the answer must be yes .. to varying luminosities .. and depending on the different states of the different parts of the gas body and the nature of the imposed energy).
To sustain any spectrum, clearly energy of some form would have to be added continuously at a fairly precise rate also. There must be other very particular constraints. Such as the pressure and density of the gas, the intensity of energy, the time variations over which the energy is applied, the regularity of the energy additions (if continuous), etc.
The presence and nature of such imposed energy must be precisely shown by the spectral lines, which in the case of the Tempel 1 impact event, clearly varies over time (30, 40 minutes to hours, days). If it doesn't vary, then the process causing the spectra would be continuous (or smoothly varying), over that same timeframe and the conditions of the gas must not vary, either.
Cheers & Thanks.
22-11-2010, 10:36 AM
The answer is no.
Quantum mechanics states that the time for an energy transistion to occur such as an electron moving back to it's ground state is related to the energy difference between the excited and ground state. The larger the difference the faster the time for the transistions to occur.
Since a gas can undergoe various transistions at different energy levels none of the transistions occur simultaneously.
A spectrum is simply a record or snapshot of these transistions over a particular exposure time.
The intensity of the peaks in either an IR absorption spectrum or IR emission spectrum relates to the concentration of the functional group causing the peak. Unfortunately this is not an absolute value.
By taking two IR spectra at different time intervals, any variations in the peaks allows one to calculate the emission rate of material from a comet.
As seen in the Japanese paper this is not a straightforward process.:)
22-11-2010, 11:35 AM
Ok. Got it - that's at the atomic scale of things. I think I was thinking of a 'cloud of gas' scale - one part of the cloud could be in the emission state another part of the same cloud could be in the absorption state ? (ie: different temperatures in the cloud).
Yep. I noticed that they calculate the amount of gas, (in molecules), by integrating the area under the peaks, over the timeframe during which they occur. This seems to be the answer to Alex's question of how they calculate the volume of gases instantaneously expelled .. and by doing this at different times, they can take the differences and work out how long it'll take for the nucleus to sublimate completely.
Also, for emissions: if the external energy (doing the excitation) has regular (or irregular) fluctuations (in terms of frequency), would the discharge emission frequencies also fluctuate ? Ie: higher frequency lines would appear and disappear ? -This being due to the amount of energy being delivered, being proportional to frequency of the excitation ? (Ie: the power/frequency distribution function).
22-11-2010, 01:21 PM
In this particular case no. You have a thermodynamic change of state with CO2/CO and H2O solids being converted into CO2/CO and H2O gases.
The solids will produce an absorption spectrum and the gases an emission spectrum since thermal energy has been absorbed by the solids to produce the gasses. IR is therefore emitted by the gasses.
Consider the energy of the exciting radiation. It is defined as E=hv. h is Plancks constant, v is the frequency of the radiation.
An atom is composed of increasing energy levels that may or may not be occupied by electrons. For absorption of radiation by the atom to occur there needs to be a difference between 2 energy levels that equals the energy of the exciting radiation. Electron(s) are pushed into the higher energy level and photons are emitted when the electron(s) drop back into the lower energy level.
If you change the frequency of the exciting radiation, E changes and absorption no longer occurs.
22-11-2010, 03:28 PM
Sorry for my persistence here and thanks so much from your answers. I really do appreciate them. They are certainly keeping me on track & I'm doing lotsa reading at the same time, also.
So what of flourescence ? (Eg: as in Tempel 1's 'Solar pumped flourescence'). I understand that flourescence happens when a substance absorbs light (or EMR) of a different frequency to that which the substance emits (which ends up being a lower frequency).
The reverse can also happen
the emitted light can end up being of a greater frequency, than what it absorbs.
So, in this case, if you didn't know the frequency of the exciting energy source, you could still work backwards from say, a particular higher frequency spectral line, to see what the frequency of the original exciting source was, and thus guess, as to where it might have come from.
I guess you could only do this if you know what the flourescing substance is to start with. I gather it would be possible to work out what the substance is, from the lower frequency absorption spectrum pattern (perhaps, in a different band), which should match with known substances ?
If the original exciting source was broad spectrum and high energy, there would be lots of flourescence, ie: emission lines corresponding to every element and compound in either crystalline (solid) or gaseous state in probably, all bands (?). If there's not a lot of flourescence lines, then the exciting energy can be assumed to be fairly low (?)
If the exciting source was broad spectrum, sporadic or irregular, and high energy, then the spectrum would change from measurement to measurement. If it were continuously broad spectrum and high energy the lines would be persistent from photo to photo (?)
Sorry about all my questions .. I don't expect a big answer
if I'm way off beam just tell me and I'll go away and read up more !
PS: I notice phosphorescence is just a 'slow release' form of flourescence.
22-11-2010, 03:42 PM
Thanks Craig and SJ! great thread.
Yeah, how to they *know* it is expelled?
To me this is a time varying measurement of existence. So i take it this tells us nothing of the function of how it came to be.
22-11-2010, 05:16 PM
(Gee I hope this thread has been of benefit to other folk also) !
Other than nucleosynthesis by a star, I don't know how else the gas could've appeared where it it is.
Can you elaborate on other possibilities ?
22-11-2010, 07:06 PM
The electric comet theory is the theory of the formation of these 'gases' from electrical processes.... that is combining with the sputtering of the surface material of the comet.... similar processes to those investigated by LCROSS
The ideas and processes are not as far out as you may think.
22-11-2010, 07:26 PM
But there's no spectroscopic evidence of 'sputtering' !
(Which is the source of all that you say, which follows !)
22-11-2010, 08:30 PM
Is there any on the moon? asteroids?
22-11-2010, 08:46 PM
I don't know.
The moon has jets though...
... and the astronauts weren't 'sputtered' during the moon landings !
now there's an ugly image !
22-11-2010, 08:52 PM
There is plenty of sputtering on all of these objects.
Your question is: Is there evidence of eletrical arc (or glow) discharge in a detectable range of the onboard equipment.
Sputtering happens with or without and answer of yes to the above question.
ie... happens on the moon, due to bombardment of solar wind. comets experience higher levels of this bombardment, sputtering is guaranteed to happen on the comet whether it be ice, rock or marshmallow.
If you can't see this simple fact, we have much to do!
22-11-2010, 09:19 PM
So electric comet theory can explain all these things yet there is no evidence at all to backup the claims, just hypotheses.
And also, the solar wind does not have an effect on the nucleus of a comet from what i have read, it doesn't reach the nucleus at all!
22-11-2010, 09:53 PM
No problems Craig.
A lower frequency emitted photon can occur if electrons jump more than one energy level. On return to the ground state a photon may be emitted for each energy level the electron drops back into in which case the sum of the emitted (lower frequency) photon energies for each level equals the energy of the absorbed photon. Alternatively it might drop straight back to the original level and have the same frequency as the absorbed photon.
You can't as the emitted photon will not have a higher (frequency) energy. If it did and the atom returns to it's ground state this would violate the conservation of energy. (Where did the emitted photon get it's extra energy?)
What can be done is to attempt to reproduce the comet conditions in laboratories to get a matching spectrum. For example as has already been seen, NASA have deduced the particle size of the jets by IR analysis of ice particles on Earth of different sizes until they got a matching spectrum.
I'm not sure what you are stating here.
If a material is absorbed at a particular wavelength it doesn't matter whether the spectrum of the exciting radiation is monochromatic, variable frequency or composed of lines and bands. (The Sun as an exciting source has a continuous spectrum). If the exciting radiation contains the wavelength at which absorbance occurs, the spectrum of the emitted photon will essentially be the same.
22-11-2010, 09:59 PM
Why don't you explain how an EC can reproduce the IR spectrum.
23-11-2010, 10:14 AM
Not simple to me where is the Bremsstrahlung that would be associated with sputtering?
23-11-2010, 10:28 AM
The electric comet theory has already made prior predictions for many of the anomalies encountered by the recent comet missions.
I would welcome any predictions of the dirty snowball sublimating puff ball hypothesis, so that i may understand and compare the models.
"no evidence at all" is a statement seeking to dismiss these 'prior' published predictions. 'No evidence at all' rarely makes it into peer reviewed engineering journals and ICOPS conferences. ;)
If the 'solar wind' was totally removed from existence, there would be a difference in cometary display and surface activity, so it does 'have an effect'.
Of-course there is an insulating plasma sheath surrounding the comet.
Are you saying that if the solar wind did not exist, we would receive no change to the nucleus activity? Is this a prediction of the dirty snowy puff balls?
23-11-2010, 10:33 AM
Which is exactly my question, do we have an on board sensors for this?
Also, what is the explanation of Temple1's pre-impact flash?
EC's is the discharge that craig seeks. Did the onboard capture this? or did it BLIND the camera by saturating the pixels (http://www.thunderbolts.info/tpod/2005/arch05/050719deepinterim.htm)?
23-11-2010, 11:36 AM
A bit obscure (and a second order effect anyway), but its called Two-Photon Absorption (TPA). From Wiki:
Ok. I was wondering whether variations in the exciting source would turn up somehow in the spectrum. Thinking more about this, I think it would simply mean that if you took 10 spectra over a short period of say, a couple of seconds, there might be differences when you compared them against eachother. From these differences, you might be able to describe the time domain nature of the exciting energy. If this was different to the continuous energy radiated by the Sun, it may be reasonable to deduce that it came from some other source. These differences would only be evident however, if you intentionally went looking for them by taking multilpe spectra over short intervals. How short ?? Who knows !!
Thanks for your help.
23-11-2010, 12:39 PM
For one i never said that the solar wind didn't exist, and two is that just because EC theory predicted something there is no way they can prove that the observed phenomena had anything to do with the "predictions"
23-11-2010, 12:56 PM
The pre-impact flash.......when you look at the video there is an impact, a brief ejection of material behind the impactor then an almighty explosion. (The video i have saved shows this, i haven't been able to find it on the web again)
On the surface of it, my initial thoughts were the impactor broke through the surface or "crust" then released it's energy below the surface as it vaporised.
The pre-impact flash may not have been exactly that, it could have been the actual initial impact.
Of course Alex wouldn't swallow this, but to me thats how i interpret it.
Of course we'd need more information about the impact itself to determine anything.
23-11-2010, 12:59 PM
I know you didn't say that the solar wind didn't exist.
I was pointing out the logically inconsistencies in your argument.
You say the solar wind does not have any effect on the nucleus.
For this to be logically coherent, we could then remove the solar wind without any resulting effect or change on the nucleus.
The Electric Comet theory suggests this cannot be done. No solar wind = big changes on the effects on the nucleus.
I tend to think both models require the solar wind to explain the nucleus activity, maybe you are suggesting something different?
Which is why we are exploring the details of the instrumentation, chemistry and physics involved in this very thread!
23-11-2010, 01:06 PM
I am happy to examine your interpretations as they crystallize.
Ofcourse they would carry more weight if they were made prior to the event.
I, as an inquisitive layman, will also hold these ideas accountable qualitatively as a complete picture develops. IE: Ideas will need to be logically consistent across all phenomena.
Maybe we could look at the expectations of a projectile 'breaking through surface crust' then vaporizing "BELOW", resulting in a below crust explosion causing such a large emission?
I would expect that should this interpretation you have suggested actually happened, we would've seen a noticeable increase in H20 IR and some form of 'ejection of material', particularly the crust which you are suggesting is 'blown apart'? This does not seem to have occurred?
* What do you suggest the crust is made from? if no surface ice detected?
* Given the size of the explosion (blinded the camera to saturation levels), would the vaporization blow out this crust? It would have to yeah... if thats what you are claiming we see?
A clear qualitative difference between these 2 ideas is that, electrical discharge does *not* require large explosions of matter to explain the pre-flash *or* blindingly large flash. Snowball seems to require this in great amounts.
But hey lets explore these ideas.
23-11-2010, 01:20 PM
I found a couple of very interesting papers, which seem particularly relevant to this discussion.
The first is Spectral Analysis of the Chandra Comet Survey (http://arxiv.org/pdf/0704.1648v1) 12th April, 2007.
These guys looked at X-Ray spectra using Chandra of 8 comets including Tempel 1, C/1999 T1 McNaught Hartley (is this Hartely 1?) and several others.
Particularly interesting is their focus on the effect of the plasma solar winds on each of these comets during their observation periods.Here's a quote for Temple 1:
A good paper .. particularly relevant to Alex's cause. It speaks of ion impact effects etc.
I was heartened to find that there are some attempting to look into the effects and impacts of the Solar wind on Comets !
I'll do another post about the second paper.. Coming up.
23-11-2010, 01:28 PM
Alex, this is from "Introduction to Comets" (John C Brandt, Robert D Chapman - 2004)
A comet presents an interesting obstacle to the solar wind. The solar wind does not see the nucleus, and it's interaction with the dust and neutral species is limited.
The cometary plasma, consisting of ionised molecules and electrons, is a serious obstacle. The ionised molecules cannot cross the magnetic field lines in the solar wind and an interaction takes place. Comets can be considered "soft" obstacles because of the way the ions get onto the field lines. The neutral molecules are released from the nucleus by sublimation and flow away from the comet at approximately 1km/s. The ions are produced by photoionisation (an easily modeled process) and the lifetimes are such that this occurs over a wide range of distances. When ionisation occurs, the ions are trapped on the field lines. This is called 'mass loading' and, because the ions are essentially at rest with respect to the solar wind speed of 450km/s, the flow is slowed. Near the comet this effect is strong, but is weak well away from the comet. Thus, the field lines wrap around the comet like a "folding umbrella" to produce the general picture due to Alfven described in sections 1.7.2 and 4.4.2.
NB - I might add that further into this chapter there are results obtained by in-situ spacecraft which correlate the information given here.
If you want to know more i suggest you buy the book and read it!
23-11-2010, 01:46 PM
Ok .. don't worry about that second paper. It seems to go on about some other theory about how comets are formed. We can do without that at the moment. ;)
It seems that there are several theories about the Tempel 1 Impactor generating more energy than was expected. Some papers talk of chemical exothermic reactions caused by the comet chemicals upon impact, others talk of rebound effects, etc.
Interesting also, (I note), is that twenty and ten seconds before the impact (that is, ~ 200 and 100 km distant from the nucleus), the Deep Impact impactor suffered two collisions with large dust particles that disturbed its orientation (AHearn et al. 2005b).
So things were happening before the impactor impacted !!
This could also explain the pre-impact flashes.
It doesn't have to be electrical discharges, Alex.
23-11-2010, 02:52 PM
Of-course it doesn't have to be, but we can keep in mind the associated expectations of all proposed causes. Here we can then build a qualitative description of what is going on, so i (we) can understand the model.
EC theorists (not me) made these mentioned predictions prior to the impact, as it was an expected feature from an already existing holistic model. Call me crazy but i see merit in predictions.
Can we please have this coherent view from the snowball team? Surely it can be explained to layman like us? A theory should be able to do these things?
Re OutbackManyEp: I get you now... yes i have acknowledged the insulating plasma sheath, in my first reply to you.
23-11-2010, 03:05 PM
Up to this stage the discussion has been based on comparing the energy of a single absorbed photon to the energy of a single emitted photon.
The energy (and frequency) of the emitted photon is determined by the energy spacing levels in the molecules not the incident photons.
The incident photons are only there to supply energy to push the electrons into higher levels. It is immaterial whether this is accomplished by 1,2....n photons at a lower (frequency) energy compared to the emitted photon. The point is the sum of the energies of the incident photons cannot be less than the energy of the emitted photon as this will violate the conservation of energy.
The 2 photon absorption effect is a very good example of why a variation in the incident radiation doesn't effect the spectrum of the molecule. The emission line or peak is at the same frequency irrespective if it took 1 absorbed photon at a higher frequency or 2 absorbed photons at a lower frequency to supply the required energy for a electron transistion to occur.
If you saw a variation in the spectra with time there are 3 possibilites.
(1) There has been a change in the physical state of the object.
(2) There has been a thermodynamic change.
(3) There has been a chemical change.
For (1) Consider the NASA spectrum of Hartley 2 and the comparative ice samples. http://epoxi.umd.edu/3gallery/20101118_Sunshine2.shtml
Note the OH peak seems to have disappeared from the 100 micron lab ice spectra. This is an example of IR scattering where the sample being tested is much thicker than the IR wavelength range. This can also apply to Vis-UV radiation except the thickness limit is much greater as Vis-UV photons have much more energy and do not scatter as readily.
(2) Has already been discussed. The conversion of comet ice to gas can change the spectra.
(3) Let me give you a down to Earth example. IR spectrometers are used to check the oxidation stabilty of engine oils. The IR spectrometers produce constant IR radiation.
Fresh engine oil does not contain the carboxyl peak (the same peak that is found for CO2). When the engine oil oxidizes the carbonyl peak "grows" with time.
23-11-2010, 03:15 PM
You are either missing the point or dancing around it.
If your comet jets are an example of sputtering then Bremsstrahlung which extends into the IR region would have been detected.
This would result in a spectrum devoid of peaks.
23-11-2010, 03:28 PM
Back to Bremsstrahlung, Alex ?
As I understand it, this produces a different looking spectrum ?
PS: [EDIT]: Steven's post#117 beat mine somehow !!
23-11-2010, 03:50 PM
Bremsstrahlung is a continuous spectrum. In the IR region (thermal Bremsstrahlung) it would be quite featureless compared to the IR spectrums showing H2O and CO2.
Alex still has to address the hydroxyl radical in all of this.
23-11-2010, 03:51 PM
Yep, totally, trying to find literature to examine on level expectations of Bremsstrahlung with EDM, to compare with spectro instrumentation.
Thanks for this.
23-11-2010, 03:54 PM
I thought the radical was off the available charts? This does not exclude it from existence, i'd be interested if we do have a measurement on this tho?
Do you mean associated hydroxyl? The LCROSS electro-formation of H20 process has shown this is possible. I'm trying to find expectations of this process within an insulating plasma sheath.
Oh yea, Can i have a coherrent answer to my questions above too? fairs fair ;)
23-11-2010, 04:30 PM
A couple of things, they did detect surface ice on 9P/ Tempel 1!
The sublimation of ices produces a porous dust mantle, this insulates the ices beneath the surface and perhaps regulates the rate of sublimation. The sublimation is believed to occur a few cm below the surface and the porous surface allows gases to permeate and escape. Heat flow through the surface provides the mechanism for this to happen. This is compatible with surface temps around 320K and for sublimating ices at 215K.
It has been observed that this process is not unform over the entire surface.
Infrared observations by Vega 1 and Deep Space 1 show that the surface temps of Halley and Borrelly were 312K and between 300 and 345K respectively.
Mind you water ice only really takes off for most comets at 3AU from the Sun, at further distances other ices begin to sublime, CO2 at 10AU, CH2O at 18AU etc.
23-11-2010, 04:38 PM
"A couple of things, they did detect surface ice on 9P/ Tempel 1!"
hmm it was 99.975% *not* surface ice on Tempel 1?
So are we saying a "porous dust mantle" can support a spikey pinnacle hundreds of meters high? and kilometer sheer cliffs?
23-11-2010, 04:38 PM
23-11-2010, 04:56 PM
Another thing i noticed on the images of 19P, 9P and 103P is that the smooth areas (which on 103P indicate an area of water ice sublimation) occur in the central regions of the nucleus.
23-11-2010, 05:08 PM
Who ever said that a comet had 100% surface ice? Is that what you were expecting to find?
A porous dust mantle does not necessarily mean it is uniform over the entire surface or that it's uniform for all comets observed.
Do you see any spikey pinnacles on 103P, 19P and 9P????? :shrug:
Anybody that has seen the images of 81P will see that it is different from the other 3 i mentioned.
23-11-2010, 05:28 PM
One of the things Ms Sunshine mentioned during the press conference was something about the dust collecting in the centre region. She (very briefly) alluded to gravity being involved. I think that might have a bit of a blooper!
The thing is too small to have any gravity. Perhaps the dust collects in the centre bit because that's where the axis of rotation is ?
Whaddya reckon ?
PS: (Talking about Hartley 1 here).
24-11-2010, 07:04 AM
Announced this morning:
Stardust-NExT successfully fired its engines for the Tempel 1 revisit (http://www.physorg.com/news/2010-11-nasa-spacecraft-comet-flyby.html) (on Nov 20). Intercept date is Feb 14, 2011:
24-11-2010, 07:38 AM
OK. I know this thread is a monster thread, but I've just gotta ask this question:
"Why is a Bremsstrahlung spectrum continuous, without peaks ?"
24-11-2010, 08:16 AM
If 103P didn't have any gravity it wouldn't exist i would think!
It may have a very insignificant amount but enough to keep most of it together!
24-11-2010, 09:10 AM
Ok .. point taken. Won't argue against the matter having some gravity. ;)
I would think however, that the thing which keeps it together would be the chemistry of the 'glue' (whatever that substance might be) .. ie: mainly ionic bonds, etc.
The 'infalling' dust, following a CO2 jet outburst is what Sunshine was alluding to. Ie: why do particles of dust collect in the centre of the thing ?
There could be lots of answers for this and I would've thought 'gravity' would have fallen a fair way down the list. (In a turbulent, energetic atmosphere, of mixed particle sizes, there are lots of forces at play).
Anyway, just thought it was an interesting phenomenon to ponder .. I'm not pushing any one particular 'bent' about it all - its too complex for that
24-11-2010, 09:38 AM
Yeah i immediately thought that didnt make any sense
24-11-2010, 09:39 AM
unless it was a rock
24-11-2010, 09:46 AM
Or a chunk of water/CO2 ice, or a big snowball with some melted ice bits, or some kind of hydrocarbon gunk, or any of the above !
Have you accounted for the low mass and density measurements, yet Alex ?
Lets get back on track, eh ?
24-11-2010, 09:55 AM
A single rock Alex? I don't think so
24-11-2010, 10:08 AM
The dust areas in the centre appear to be an area where water vapour is being ejected from the comet according to the EPOXI images, if the surface is dusty then it could mean that it's porous, if that's the case then there could be something going on under the surface. The CO2 is noticable as at the heliocentric distance the comet was at the time CO2 would have been highly volatile.
24-11-2010, 11:44 AM
Let's define what a peak (or line) is in an emission spectrum.
An emission spectrum is like a histogram defining the distribution of the number of emitted photons that fall on any particular wavelength. In a line emission spectra the photons fall into discrete frequencies which corresponds to the transistion of electrons over the energy levels.
In Bremsstrahlung, photons are emitted by the deacceleration of charged particles. The frequency of the photon is determined by the magnitude of deacceleration. The magnitude of deacceleration is random hence photons are emitted over a wide range of wavelengths.
As is no "preferred" wavelength the distribution of photons is essentially even. Hence the spectrum is continuous instead of discrete, and peaks and lines are not evident.
It is possible for absorption lines to be superimposed on a Bremsstrahlung spectrum if the charged particles absorb some of the Bremsstrahlung energy.
24-11-2010, 12:07 PM
Very interesting .. might have a good think about that one
17-06-2011, 09:33 AM
The Latest EPOXI Findings on 103P/Hartley by Ahearn et al, have been published (16th June).
I thought I'd add the below info to this thread just for completeness .. (no mention of sputtering or electrical discharge, mind you .. ;) )
Latest EPOXI findings on Comet Hartley 2 published (http://www.physorg.com/news/2011-06-latest-epoxi-comet-hartley-published.html)
Main findings are:
The latest reports (April 2011) are here:
The Carbon Monoxide Abundance in Comet 103P/Hartley during the EPOXI Flyby (http://arxiv.org/pdf/1104.4477v1) and ..
Rotation of Comet Hartley 2 from Structures in the Coma (http://arxiv.org/pdf/1104.4672v1).
17-06-2011, 01:09 PM
Anything the EU say is a lost cause...all the results (including the latest) explain more than adequately what's going on.
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