Evidence of life from the spectrum of exoplanets?

[repoman]

Anyone have any input on this? Obviously if there was an earth clone out there, it would be easily recognized by this method. Perhaps the fact that photosynthesis and not chemosynthesis drives life now makes the earth's spectrum a sure thing for life.

But what about other types of life? Wouldn't it have to contain a lot of chemicals that would tend to breakdown instead - but exist because life is replenishing them?

Also, the atmospheres of Jupiter and Saturn almost totally rule out life don't they?

 

[Bomb#20]

Anyone have any input on this? Obviously if there was an earth clone out there, it would be easily recognized by this method. Perhaps the fact that photosynthesis and not chemosynthesis drives life now makes the earth's spectrum a sure thing for life.

Keep in mind that we don't actually image extrasolar planets. The way we find them is by noticing the Doppler shift in the parent star's velocity toward or away from us, which gives us only the planet's orbit and mass, or by detecting the drop in brightness when the planet passes in front of the star, which gives us only the planet's orbit and diameter. The former method doesn't even give a hint at the spectrum. To get a spectrum from a transiting planet, you'd need to distinguish the light passing through the planet's atmosphere from the light that misses the planet altogether. An earth clone would be detected by a drop in the star's brightness of about 1 part in 10,000; and the atmosphere is about 10 km thick on a planet with a radius of about 6000 km, which bumps the required sensitivity up to about 1 part in 3,000,000. So we're talking about detecting an oxygen atmosphere by taking a star's usual spectrum, taking the spectrum again during the transit, subtracting, and observing, not Fraunhofer lines, but Fraunhofer 1/3,000,000 brightness dips.

So I wouldn't expect to recognize an earth clone by its spectrum until we have a space telescope so big it can image the planet. (And collect so much light we get a spectrum rather than a few fuzzy pixels!)

But what about other types of life? Wouldn't it have to contain a lot of chemicals that would tend to breakdown instead - but exist because life is replenishing them?

Also, the atmospheres of Jupiter and Saturn almost totally rule out life don't they?

Life not based on water and nucleic acids? Haven't a clue.

 

[repoman]

That sounds like a very big telescope indeed. It would have to be a visible/near IR telescope, right?

There must be a formula for how big the telescope would have to be to find solid evidence for molecular oxygen (on a twin earth) per light year.

like K = meters/light year. What is K?

How well can optical scopes be arrayed like radio scopes?

 

[crispy]

Are they listening to the radiowaves emitted from the exoplanets?

 

[fromderinside]

Are they listening to the radiowaves emitted from the exoplanets?

 Contact (1997 US film); Signs of Life http://stardate.org/astro-guide/btss/extrasolar/signs_of_life

 

[fromderinside]

How well can optical scopes be arrayed like radio scopes?

Take a look

 

[bilby]

How well can optical scopes be arrayed like radio scopes?

Take a look

The detection of planetary atmosphere spectra will have to wait for funding of the Unimaginably Large Telescope, the Inconceivably Huge Telescope, or the Fucking Vast, No, Really, It's Bloody Collossal Telescope.

Unless astronomers decide to go back to imaginative, rather than descriptive names for the tools of their trade.

 

[fromderinside]

Take a look

The detection of planetary atmosphere spectra will have to wait for funding of the Unimaginably Large Telescope, the Inconceivably Huge Telescope, or the Fucking Vast, No, Really, It's Bloody Collossal Telescope.

Unless astronomers decide to go back to imaginative, rather than descriptive names for the tools of their trade.

Actually those signatures are available in today's spectroscopic signals. Its just that they are very small and very likely to be masked by other signals. Proper modeling should fix the problem. As movements of exoplanets become more precise atmospheric signatures should be recoverable. Its just a matter of applying  Signal averaging magnifying S/N ratios of target signal through repeated targeted information captures. The target would be tracked spatial location of object, the signal would be consistent atmospheric signatures and all else would be considered noise. We've been doing that in EEG work for about 60 years. I'm pretty sure astrophysicists have been doing it even longer.

 

[Mageth]

Keep in mind that we don't actually image extrasolar planets.

We actually do...currently limited to very large planets relatively far away from their stars, and requiring sophisticated imaging techniques...

http://arstechnica.com/science/2013/03/atmospheric-analysis-reveals-an-exoplanet-thats-as-alien-as-can-be/

http://arxiv.org/abs/1307.2886

 

[Mageth]

A lot of progress has been made in exoplanetary atmospheric analysis...just one example:

http://arxiv.org/pdf/1406.7567v1.pdf

 

[Bomb#20]

Keep in mind that we don't actually image extrasolar planets.

We actually do...currently limited to very large planets relatively far away from their stars, and requiring sophisticated imaging techniques...
...
A lot of progress has been made in exoplanetary atmospheric analysis...just one example:

Sorry, I meant we don't image Earth-sized extrasolar planets; my calculation of required sensitivity was for a hypothetical Earth clone. Getting spectral information from a Jupiter clone would take at least a hundred times less sensitivity.

 

[Malintent]

Keep in mind that we don't actually image extrasolar planets. The way we find them is by noticing the Doppler shift in the parent star's velocity toward or away from us, which gives us only the planet's orbit and mass, or by detecting the drop in brightness when the planet passes in front of the star, which gives us only the planet's orbit and diameter. The former method doesn't even give a hint at the spectrum. To get a spectrum from a transiting planet, you'd need to distinguish the light passing through the planet's atmosphere from the light that misses the planet altogether. An earth clone would be detected by a drop in the star's brightness of about 1 part in 10,000; and the atmosphere is about 10 km thick on a planet with a radius of about 6000 km, which bumps the required sensitivity up to about 1 part in 3,000,000. So we're talking about detecting an oxygen atmosphere by taking a star's usual spectrum, taking the spectrum again during the transit, subtracting, and observing, not Fraunhofer lines, but Fraunhofer 1/3,000,000 brightness dips.

So I wouldn't expect to recognize an earth clone by its spectrum until we have a space telescope so big it can image the planet. (And collect so much light we get a spectrum rather than a few fuzzy pixels!)

But what about other types of life? Wouldn't it have to contain a lot of chemicals that would tend to breakdown instead - but exist because life is replenishing them?

Also, the atmospheres of Jupiter and Saturn almost totally rule out life don't they?

Life not based on water and nucleic acids? Haven't a clue.

You describe only one method of detection

There have been multiple extraplanets that have been directly observed. Granted, the information we can get from that method is only a pixel or two in resolution.