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Top Biosignatures for exo planet spectra

  1. Jan 30, 2012 #1
    What are the top bio signatures we should be looking in exo planet spectra?
    What sort of telescope would be needed to obtain good spectra of potential Earth twins? Would it require Darwin or TFP or could something cheaper obtain such spectra?
  2. jcsd
  3. Jan 30, 2012 #2
    Ozone would be a good indicator, as the production of it requires a large amount of Oxygen to be present. The oxygen would need to be replenished by something, which is most likely to be life.
  4. Jan 30, 2012 #3
    Thansk for that, so apart form that and the red edge , what else should we be looking for and what telescopes might be able to find it? Any terrestial ones or will it need TPF or Darwin?
  5. Jan 31, 2012 #4


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    I think our only real hope, besides SETI, is to search for non-equilibrium chemistry. The aforementioned oxygen in the atmosphere is one example, but in general any chemistry that is out of equilibrium will do.
  6. Jan 31, 2012 #5
    But if I look at aspectrum ,exasctly what does an out of equilibrium chemitry look like?
  7. Jan 31, 2012 #6


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    Basically, you're looking for a combination of molecules that would tend to combine to form other elements. Free oxygen is a dead-ringer here, because free oxygen combines with just about everything common on a rocky planet: hydrogen, carbon, iron, silicon, etc. So oxygen simply will not stay in an atmosphere all that long unless it is continuously replenished.

    Unfortunately my chemistry isn't all that good, so I couldn't tell you what else would count as an out-of-equilibrium chemistry. But that's the basic idea: a combination of elements that would change dramatically if given the chance.
  8. Jan 31, 2012 #7
  9. Jan 31, 2012 #8
    Oxygen is good, and oxygen + organic compounds is even better. Oxygen + methane, for instance.

    One ought to consider what can get into an atmosphere, because gas-phase materials have relatively narrow and distinctive spectral lines. Condensed materials tend to have relatively broad ones. So that's why oxygen + methane is so good.
  10. Jan 31, 2012 #9
    Chlorine + water or even better organic compounds would be another tracer for extraterrestrial life.
  11. Jan 31, 2012 #10


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    The identification of oxygen atmospheres on extrasolar planets through detection of ozone is not necessarily evidence of biological processes. Irradiation of water ice is known to produce spectroscopically detectable levels of ozone. The Hubble detected ozone in the atmospheres of Saturn's moons Rhea and Dione about 20 years ago. Both are known to have significant quantities of water ice on their surfaces. Both moons also reside in the radiation belt of saturn. Since water ice is believed to be abundant in the cosmos, we could be misled by an ice rich planet with a strong ozone line in its spectrum simply caused by ionizing radiation. NASA is, of course, aware of this situation. It remains uncertain what atmospheric markers would be conclusive evidence of biological processes on exoplanets.
  12. Feb 1, 2012 #11
    That's why detecting the qualitative composition is not sufficient. A quantitative analysis is required to proof that the atmosphere is out of equilibrium.
  13. Feb 1, 2012 #12
    But what exactly does that ential? Any refercne to where this has been modelled in the literature?
  14. Feb 1, 2012 #13


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    Well, I think in the end if we ever detect the atmosphere of an exoplanet that looks like it may have an out-of-equilibrium composition, there will be a long and in-depth scientific discussion about whether this is actually the case or not. I think that the exact nature of the discussion will focus quite strongly on the specific planet and the specific claimed evidence in favor of it being out of equilibrium.
  15. Feb 5, 2012 #14
    I guess we want a 'wow' signal of oxygen. Who cares about fiddly trace contents.
    we have found those in this solar system anyway and are still debating them even after landing probes.

    People focus on finding any success at any level. I think it would also be interesting if we found one clear failure: One world for which isn't too hot like venus, isn't too cold like mars, has liquid water and so on, but does not have any obvious signal of life. (Earth would be pretty frigging obvious if you get any look at its spectrum I imagine? 25% oxygen!.. and it has been that way for billions of years hasn't it?)

    One good failure would say life does not just happen if you throw all the ingredients together. It needs something else, perhaps one spectacular roll of the dice that may not happen in every galaxy or even universe.

    On a different topic but related to the OP,
    here is an article about detecting photosynthesis. Don't know if it is valid.
  16. Feb 6, 2012 #15
    Thanks for that, one issue with estimating planets surfacer temeprature is the level of greenhouyse gases, we cnat just work out the flux that would tell us Earth is too cold for life.
    Btw , sorry for this thread being in the cosmology section, not sure how to move it.
  17. Feb 6, 2012 #16
    You can put in a request to staff members with the "Report" button at each post.

    First, what's so good about oxygen-releasing photosynthesis? It enables using something very common as an electron donor: water. That means that O2-releasers can support a very large biota, a biota that can include large populations and total masses of eaters of them and eaters of eaters of them etc.

    There are photosynthetic organisms that can use other electron donors, organisms like the green and purple bacteria. They use electron donors like iron (Fe++ -> Fe+++), hydrogen, sulfides, and sulfur. These are much less common than water, making their users' biomass productivity much more limited.

    As to looking for spectroscopic evidence of photosynthetic pigments, there are some problems. At first sight, it might be "Look for a spectral line of chlorophyll", but there are several problems with that approach.

    Spectral lines of condensed-state materials are often much broader than gas-phase spectral lines: Absorption Spectra of some photosynthetic pigments.

    Organisms use a variety of photosynthetic pigments:
    • Chlorophylls
    • Carotenoids
    • Phycobiliproteins
    • Bacteriorhodopsin
    So extraterrestrial photosynthesizers may use any of these, or some different ones.
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