ITN: CO2 Powers Hartley !

[CraigS]

Some of the science results of the EPOXI flyby of Hartley 2 are just starting to come out …

Primordial dry ice fuels comet jets.

Of great interest is the comment by Jessica Sunshine[/URL] (deputy principal investigator for the EPOXI mission):

"We now have unambiguous evidence that solar heating of subsurface frozen carbon dioxide (dry ice), directly to a gas, a process known as sublimation, is powering the many jets of material coming from the comet. This is a finding that only could have been made by traveling to a comet, because ground based telescopes can't detect CO2 and current space telescopes aren't tuned to look for this gas," Sunshine said.

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 is no slouch in spectroscopy ..

Jessica is an expert in analyzing spectra to remotely infer the composition of asteroids, meteorites, the moon and Mars..
Jessica is a Principal Investigator in NASA's Planetary Geology and Geophysics Program researching the composition of asteroids and meteorites.

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.

Cheers

[Max Vondel (Peter)]

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.

[mswhin63 (Malcolm)]

I thought this thread was about powering motorbikes with CO2, gobal warming issue

[AdrianF (Adrian)]

Originally Posted by mswhin63

I thought this thread was about powering motorbikes with CO2, gobal warming issue

Me too.

Adrian

[CraigS]

Originally Posted by AdrianF

Me too.

Adrian

Ooops !!

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) !!

Cheers

[CraigS]

Originally Posted by Max Vondel

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.

Hi Peter;
Yes … 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 !!

Cheers

[sjastro]

Originally Posted by CraigS

Hi Peter;
Yes … 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 !!

Cheers

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.

Regards

Steven

[CraigS]

Originally Posted by sjastro

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.

Regards

Steven

G'Day Steven;

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.

Interesting.

Cheers
PS: I still don't get her comment about the space based scopes, though.

[sjastro]

Originally Posted by CraigS

G'Day Steven;

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.

Interesting.

Cheers
PS: I still don't get her comment about the space based scopes, though.

Craig ,

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.

Regards

Steven

[CraigS]

Hmm .. Thanks again, Steven … interesting ..

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

Mark Swain, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., used Hubble's near-infrared camera and multi-object spectrometer to study infrared light emitted from the planet, which lies 63 light-years away. Gases in the planet's atmosphere absorb certain wavelengths of light from the planet's hot glowing interior. Swain identified carbon dioxide and carbon monoxide. The molecules leave a unique spectral fingerprint on the radiation from the planet that reaches Earth. This is the first time a near-infrared emission spectrum has been obtained for an exoplanet.

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 !

Cheers

[bartman (Bart)]

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!

Sorry ...other than that ... I have nothing to add to this post other than its interesting once again!

Bartman

[CraigS]

Originally Posted by bartman

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!

Sorry ...other than that ... I have nothing to add to this post other than its interesting once again!

Bartman

Hi Bart;
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.
Cheers

[DavidU (Dave)]

So it is just frozen soda water & dust then.

[CraigS]

Originally Posted by DavidU

So it is just frozen soda water & dust then.

Hi Dave;

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).

Cheers

[sjastro]

Originally Posted by CraigS

Hmm .. Thanks again, Steven … interesting ..

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



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 !

Cheers

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.

Regards

Steven

[CraigS]

Hmm;
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).

Cheers
PS: Also interesting is that the jets were coming from the dark side of the nucleus.

[multiweb (Marc)]

Originally Posted by CraigS

Hi Bart;
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.
Cheers

+1

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.

[CraigS]

Originally Posted by multiweb

+1

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.

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' ?

Cheers

[sjastro]

Originally Posted by CraigS

Hmm;
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).

Cheers
PS: Also interesting is that the jets were coming from the dark side of the nucleus.

Craig,

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.

Regards

Steven

[sjastro]

Originally Posted by CraigS

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' ?

Cheers

Perhaps Mr Pressure was deflated by the experience.
I don't think he liked my "mighty pen" remark.

Steven