ITN: CO2 Powers Hartley !

[CraigS]

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 (submitted 12 Feb 2010):

Detection of molecules via infrared spectroscopy probes the conditions and composition of exoplanet atmospheres. To date, water (H2O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot-Jupiter type exoplanets. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the important 2.4–5.2 μm spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0–2.4 μm and 3.1–4.1 μm, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements.
The feature around 3.25 μm is completely unexpected and is difficult to explain with models that assume local thermodynamic equilibrium
(LTE) conditions in the 1 bar to 1×10-6 pressures typically sampled by infrared measurements. The most likely explanation for this emission is non-LTE emission from CH4, similar to what is seen in the atmosphere of planets in our own solar system. These results suggest that non-LTE effects may need to be considered when interpreting measurements of strongly irradiated exoplanets.
…
Detection of molecules via infrared spectroscopy probes the conditions and composition of exoplanet atmospheres. To date, water (H2O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot-Jupiter type exoplanets. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the important 2.4–5.2 μm spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0–2.4 μm and 3.1–4.1 μm, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements.

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….

Cheers

[CraigS]

Ok .. so then Swain defended and refuted the challenge (sounds familiar ??):

NICMOS Ttransmission
 Spectroscopy
 of
 HD
 189733b: 
Controversy Becomes
 Confirmation
 (submitted October 20, 2010):

Spectral features corresponding to methane and water opacity were reported based on spectroscopic observations of HD 189733b with Hubble/NICMOS. Recently, these data, and other NICMOS exoplanet spectroscopy measurements, have been reexamined in Gibson et al. 2010, who claim that the features in the transmission spectra are due to uncorrected systematic errors and not molecular opacities.
We examine the methods used by the Gibson team and show that, contrary to their claim, their results for the transmission spectrum of HD 189733b are in fact in agreement with the original results.
In the case of HD 189733b, the most significant problem with the Gibson approach is a poorly determined instrument model, which causes (1) an increase in the formal uncertainty and (2) instability in the minimization process; although Gibson et al. do recover the correct spectrum, they cannot identify it due to the problems caused by a poorly determined instrument model.
In the case of XO-1b, the Gibson method is fundamentally flawed because they omit the most important parameters from the instrument model. For HD 189733b, the Gibson team did not omit these parameters, which explains why they are able to reproduce previous results in this case, although with poor SNR.

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.

Cheers

[CraigS]

Just for the record, the original paper where Swain announced the detection of H2O, CO and CO2 is here. Dated Dec 10, 2008)...

We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 μm using the NICMOS instrument on the Hubble Space Telescope. The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H2O), carbon monoxide (CO), and carbon dioxide (CO2) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules.
…
Using a radiative transfer model, we determine that the molecules H2O, CO and CO2 are likely present on the dayside of HD 189733b, and we are able to estimate abundances for these species.

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 !!

Cheers

[sjastro]

Originally Posted by Jarvamundo

hmmm... spectro Rabbit holes...

Steven can you recommend a good text on spectro? I'm intrigued.

Alex,

There is a lot of information on the Internet for general spectroscopy.

For IR spectroscopy this might be useful.
http://www.usm.edu/phillipsgroup/CHE...hapter2/IR.pdf

Regards

Steven

[sjastro]

Very interesting information you have uncovered Craig.

Regards

Steven

[CraigS]

Originally Posted by sjastro

Very interesting information you have uncovered Craig.

Regards

Steven

The bit that's still got me is the IRTF ground based facility. From Wiki:

The NASA Infrared Telescope Facility (NASA IRTF) is a 3-meter (9.8 ft) telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawaii.
…
The IRTF hosts 4 facility instruments. SpeX is a 0.8 to 5.4 micrometre low to moderate resolution (R=100 to R=2000) cross dispersed spectrograph with a parallel infrared guider.
CSHELL is a high resolution (R=30,000) single order 1 to 5.5 micrometre spectrograph.
MIRSI is a 4.9 to 25 micrometre thermal infrared imaging camera with grism spectrographic capability.
NSFCam2 is a 1 to 5.5 micrometre imaging camera with a wide range of filters suited to planetary science and a continuously variable filter (CVF). IRTF also hosts a number of visitor instruments, usually thermal infrared spectrographs.

All done from Mauna Kea !!
They also use fairly extensive adaptive optics there as well.

Haven't looked at ESO's facilities yet.

Cheers

[CraigS]

In the News this morning .. they've now released the High Resolution Camera images.

They clearly show H2O ice particles emanating from the surface !!

Also, here ya go Alex … the absorption spectrum overlaid with lab test results showing the particle size (~ 1 micron).

And the main press release is here. A few notable quotes:

Data show the smooth area of comet Hartley 2 looks and behaves like most of the surface of comet Tempel 1, with water evaporating below the surface and percolating out through the dust. However, the rough areas of Hartley 2, with carbon dioxide jets spraying out ice particles, are very different.

"The carbon dioxide jets blast out water ice from specific locations in the rough areas resulting in a cloud of ice and snow," said Jessica Sunshine, EPOXI deputy principal investigator at the University of Maryland. "Underneath the smooth middle area, water ice turns into water vapor that flows through the porous material, with the result that close to the comet in this area we see a lot of water vapor."

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. … No mention of rocks anywhere ...

Fascinating stuff !

Cheers

[Jarvamundo (Alex)]

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

[CraigS]

Originally Posted by Jarvamundo

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"

5:50 - "we think" … possibly up to the size of a basketball probably very porous.

Originally Posted by Jarvamundo

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."

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.

Originally Posted by Jarvamundo

what the? that's a pretty big contradiction?

Not really … 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.

Originally Posted by Jarvamundo

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?

A conspiracy !!

Originally Posted by Jarvamundo

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.

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 !!

Originally Posted by Jarvamundo

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

Yeah .. the cut-outs are a bit frustrating !! Why wasn't your mate Emily present at the conference, I ask ???


Cheers

[Jarvamundo (Alex)]

Shes not my Mate, shes Phil Plait's mate, who is your mate?

this is getting weird

[CraigS]

Apologies … thought you liked her questions ..

Lets get back to spectrographs and comet data ..

Cheers

[Jarvamundo (Alex)]

Lets get back to spectrographs and comet data ..

definately Craig.

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.

[CraigS]

Gee Alex;

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.

Cheers

[Jarvamundo (Alex)]

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.

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.

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

In this case, comets come with H2O already formed. So we don't have to worry about the creation of the molecules.

Yep, but this assumption swings both ways, sublimation theory will need to explain how some molecules remain there, if not 'formed' etc.

[CraigS]

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.
??

Cheers

[Jarvamundo (Alex)]

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.

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.

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)

[CraigS]

Originally Posted by Jarvamundo

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).

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).

Originally Posted by Jarvamundo

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)

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.

Cheers

[CraigS]

Oh yes … 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.

Cheers

[Jarvamundo (Alex)]

Originally Posted by CraigS

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

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)

"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."

Is this just conjecture? Is this a strawman?, or are you basing this on something solid i can investigate?

[Jarvamundo (Alex)]

Originally Posted by CraigS

O
The dust they spoke of would've stuck all over the whole spacecraft .. ever polished ya car and driven through bulldust ??

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).

Excellent thinking.

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.