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James Webb Telescope

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Mike Helland said:
CO2 in an exoplanet

https://www.universetoday.com/15730...r-carbon-dioxide-in-an-exoplanets-atmosphere/
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Interesting, but hardly surprising. The fact that JWST can detect it is the interesting/ exciting part. Unsurprising part is that a lot of planets are likely dominated by CO2 atmospheres. Venus being a case in point. Now, if it could probe the atmospheric composition of ~ Earth mass planets in the habitable zone, that would be really interesting. It will be difficult to detect diatomic molecules such as O2, but O3 would certainly be.............interesting.
 
So, I don't know much about spectrometry, but why would it be hard to detect O2 in an atmosphere? Because that's the thing that would interest me the most. Water might or might not be a sign of life, but large quantities of O2 would be a slam-dunk for life, wouldn't it?
 
Not sure that has much relevance though. The atmosphere of Venus is 96% carbon dioxide and subjected to UV light from the sun. The problem with oxygen is that it isn’t very stable and tends to react with other elements, so that O2 will diminish over time if there is not something that continuously replenishes it.
 
Puppycow said:
So, I don't know much about spectrometry, but why would it be hard to detect O2 in an atmosphere?
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The smaller the molecule, the fewer vibrational modes it has. And the double bond of O2 also increases the energy needed for the vibration it does support. For O2, this means you need a lot of energy for any significant absorption and that means UV, not IR. I suspect JWST is simply ill-suited to probing such spectra.

The extra atom in CO2 and O3 give a bending mode that's not possible for a diatomic molecule. That one is easier to activate and gives some lines in IR.
 
BowlOfRed said:
The smaller the molecule, the fewer vibrational modes it has. And the double bond of O2 also increases the energy needed for the vibration it does support. For O2, this means you need a lot of energy for any significant absorption and that means UV, not IR. I suspect JWST is simply ill-suited to probing such spectra.
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But JWST would see UV that has redshifted in to the IR.

Lat night I thought I'd be able to answer puppycow's question just by googling a few things about O2s structure and came away confused. Given O2's disassociation energy I came away wondering if O2 can exist under any circumstance where it would display spectral lines. Hopefully jonesdave116 will be back.
 
Dave Rogers said:
Only from objects so distant that it would be impossible to pick out a single star, let alone a planet, surely?
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Yeah, I left out a couple of thoughts. You're right JWST would only detect it in large clouds I would assume.

But the thought I left out is that just means puppycow's question should have come up 20 or so years ago when we first had spectrographs in space that could observe UV light (blocked by Earth's atmosphere). I presume that Hubble's spectograph would cover UV. Yet I found few reports of O2 being detected anywhere. So I'm wondering why. Is it not present in clouds where we could observe absorption lines? Maybe it's all bound up with hydrogen instead. Or is it just hard to see because it doesn't have any transitions under conditions where it's likely to exist (especially in atmospheres). That's where I got lost.

One relevant link: https://en.wikipedia.org/wiki/Space_Telescope_Imaging_Spectrograph
 
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Thanks for the explanations. Yeah, I was thinking about exoplanets in our own part of the milky way, so redshift wouldn't help there. That's sad because O2 would be a sure* sign of photosynthesis and therefore plants. The only reason earth's atmosphere has it is because plants make it.

*Maybe not 100%, because there could be some process we don't understand, but plant-based photosynthesis would be the leading hypothesis.
 
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Puppycow said:
*Maybe not 100%, because there could be some process we don't understand, but plant-based photosynthesis would be the leading hypothesis.
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Someone mentioned disassociation of CO2 above. Same thing happens with water. Seems to me any planet covered in water could potentially have an oxygen atmosphere when UV breaks up water molecules. Not sure the planet would literally have to be covered with it either as long as whatever crust was exposed was fully oxidized.
 
RecoveringYuppy said:
That's what my next sentence was addressing. If there is nothing to absorb it then it accumulates.
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Oxygen can disolve in water, and anything on the ocean floor can still react with that oxygen. Being covered in water doesn't prevent oxidation.
 
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