Would an oxygen/nitrogen atmosphere = life?

[Stranger_On_A_Train]

@John DiFool

Hoo boy we sure have a bunch of nitpicky people here. All I wanted was to have a discussion
of what would happen if we discovered a planet (via the proposed Terrestrial Planet Finder
or the like) which had a number of spectroscopic signatures of key elements and compounds
(including but not limited to oxygen, nitrogen, and water vapor)-what would be our confidence
interval basically that it would have life? What else would we need as further evidence
that the planet in question does have life?

Being nitpicky abiout is one of life’s rare pleasures.

But seriously, there’s no authoritative, straightforward answer to your question 'cause with regard to life we have only the one data point–Earth–where we definitively know life exists and what conditions indicate it. I would conjecture (despite Blake’s contention) that a planet with a strong spectroscopic oxygen band has a very high probability of having some kind of life, or at least conditions which would be very condusive to life as we know it. That doesn’t mean that the absence would indicate a corresponding low probability of life; life (even complex life) might very well exist without free oxygen. We just don’t have enough empirical knowledge to reach any definitive conclusions.

I don’t know how long it will be until we are capable of discovering those conditions on another world. Right now it stretches astronometric technology to the limit just to detect other (very large, close orbiting) worlds at nearby stars and get some very rough notions of their orbital characteristics and mass, with only speculative inferences about their composition. From a nearby star with properties for supporting life as we know it (Tau Ceti) we would be hard pressed to observe indications of Jupiter, much less the inner rocky worlds where life as we know it is likely to have developed.

Stranger

[Squink]

@Stranger On A Train

I don’t know how long it will be until we are capable of discovering those conditions on another world.

There are at least a couple of cases where exoplanet atmospheres have been detected:
Hubble Makes First Direct Measurements of Atmosphere on World Around another Star (2001)

Oxygen and carbon discovered in exoplanet atmosphere ‘blow-off’ (2004)

[Stranger_On_A_Train]

[QUOTE=Squink]

@Stranger On A Train

I don’t know how long it will be until we are capable of discovering those conditions on another world.There are at least a couple of cases where exoplanet atmospheres have been detected:

I should have qualified that as rocky worlds in a habitable zone. If life exists on Jovian-type world in close orbit to its sun, it will be nothing like what we know or probably will recognize. And the “dead” cores of gas giants which are having their atmosphere blasted away are almost certainly not going to be stable enough to support life.

Detecting the atmospheric composition of terrestrial worlds (or indeed, the worlds themselves) is beyond current capabilities, though with an orbital interferometer array like the Terrestrial Planet Finder might be capable of getting at least some indications, though unlikely sufficient to assure the existance of life.

Stranger