Can We Detect Signs of Life on Exoplanets Using Spectral Analysis?

[cph]

How far away can the oxygen signature in our atmosphere be detected? Indicative of photosynthesis. How far away can optical flashes from spaceships/satellites in Moon orbit be detected? A sign of technological civilization from afar. Is this much more effective than radio wave detection?

 

[daveb]

I suppose it would depend upon the sensitivity of the instruments used by that technological civilization. Right now, I would guess our technology is better suited to detecting faint radio signals rather than oxygen signatures or optical flashes (which is why we use radio).

 

[Cosmo Novice]

One of the interesting ideas in ET life detection is based on the Kardashev scale - in that the more a species grows the deeper its energy requirements become. Until it is eventually hypothesized they would need the entire output of a star. The detection of a Dyson Sphere or other large body equivalent is, in my opinion, as good a method of detection as SETI.

Just my two cents worth

 

[DrStupid]

The detection of a Dyson Sphere or other large body equivalent is, in my opinion, as good a method of detection as SETI.

The search for astro-engineering products like Dyson Spheres is actually part of SETI (e.g. http://www.sciencedirect.com/science/article/pii/S0094576598000150) but currently it is as unsuccessful as the search for “intelligent” radio signals. Maybe the search programs covered the wrong temperature range. I already found publications for temperature starting from 100 K (http://iopscience.iop.org/0004-637X/698/2/2075/pdf/0004-637X_698_2_2075.pdf) but I would expect Dyson Spheres to be much colder because the degree of efficiency of the energy conversion increases with decreasing outer temperature. I already tried to perfom an own search but I wasn’t able to eliminate the Zodiacal light from the IRAS data (Does anybody know how to do that?).

I would also expect that Dyson Spheres could be detected not only by their thermal radiation but also by artificial emissions. If there are structures orbiting the sphere there would be focused transmissions for communication and power supply. If parts of these transmissions miss their target they could be detected from Earth (e.g. as optical flashes as mentioned by cph). But currently there seems to be no evidence for such signals (http://frank.harvard.edu/~howard/papers/sleague.pdf).

 

[Astronuc]

How far away can the oxygen signature in our atmosphere be detected? Indicative of photosynthesis. How far away can optical flashes from spaceships/satellites in Moon orbit be detected? A sign of technological civilization from afar. Is this much more effective than radio wave detection?

The Earth and moon would be lost in the sun. One has to think in terms of light years.

Consider the solid angle subtended by the earth, Jupiter and Saturn. Which has the most impact on the sun's light at 1+ ly?

 

[DrStupid]

The Earth and moon would be lost in the sun.

I'm not sure about that. Earthlike planets can be detected using the transit method. During the passage of the planet the light of its star is not only covered by the planet. A small fraction of the light will pass the planets atmosphere and might reach Earth. Then we will not only see a decrease of brightness but also additional absorption lines in the spectra of the star - carrying information about the composition of the atmosphere. Of course a successful spectral analysis will require a very high precision but this is a technical problem that might be solved in near future.

 

[chemisttree]

I'm not sure about that. Earthlike planets can be detected using the transit method. During the passage of the planet the light of its star is not only covered by the planet. A small fraction of the light will pass the planets atmosphere and might reach Earth. Then we will not only see a decrease of brightness but also additional absorption lines in the spectra of the star - carrying information about the composition of the atmosphere. Of course a successful spectral analysis will require a very high precision but this is a technical problem that might be solved in near future.

Something like that has been done already with at least one of the so-called "hot Jupiters" that have been detected. I'm not sure spectral signals unique to various atmospheric components have been detected, though.

http://www.space.com/3673-water-extrasolar-planet-atmosphere.html
http://en.wikipedia.org/wiki/HD_209458_b