Lifeless Planets With Free Oxygen?

[Vexer]

Was going to put this the Cosmology section, but seemed better here:

 

 

Bit of a science-fiction question: are there any circumstances in which a completely lifeless planet/moon could sustain enough atmospheric oxygen to support humans?

 

Give it water or ice, or whatever it takes. But no native life of any kind.

[JMJones0424]

Water and ice both contain oxygen, but it is bound with hydrogen. Oxygen is highly reactive, second only to fluorine in electronegativity. I don't know of any chemical processes other than life that produce substantial amounts of free oxygen.

[sman]

Water and ice both contain oxygen, but it is bound with hydrogen. Oxygen is highly reactive, second only to fluorine in electronegativity. I don't know of any chemical processes other than life that produce substantial amounts of free oxygen.

 

So, oxygen means life?

 

Were we to detect free oxygen - by which I think you mean molecular oxygen, O2 - in an extra-solar environment should we assume life there? Can we even do anything like a chemical analysis of an extra-solar planet? Do these things give us enough light for spectroscopy?

 

I've heard that the methane in our own atmosphere - if detected by extra-terrestrials knowing nothing else about earth - would be a definitive indication of the life here. Now, methane constitutes about .000179% of our atmosphere, compared with oxygen at about 20%.

[JMJones0424]

So, oxygen means life?

 

Were we to detect free oxygen - by which I think you mean molecular oxygen, O2 - in an extra-solar environment should we assume life there? Can we even do anything like a chemical analysis of an extra-solar planet? Do these things give us enough light for spectroscopy?

 

I've heard that the methane in our own atmosphere - if detected by extra-terrestrials knowing nothing else about earth - would be a definitive indication of the life here. Now, methane constitutes about .000179% of our atmosphere, compared with oxygen at about 20%.

 

I don't know. Methane occurs naturally in the solar system without needing life to generate it. O₂ is a different story.

[sman]

I don't know. Methane occurs naturally in the solar system without needing life to generate it. O₂ is a different story.

 

 

Well, I can’t remember where I read about the methane, but I was obviously confused, thanks.

 

On extra-terrestrial oxygen I can find very little. Evidently, the standard method for identifying possible life on exo-planets is by comparing their spectra (so yes, apparently we can collect enough light to do this) with that of earth. But I did find one article in which the authors argue that this method will produce false negatives - that any “high simultaneous concentrations of O2, O3, CH4 and N2O” indicate photosynthesis, even if the planet isn’t green. In corollary I think this agrees with you and answers the OP squarely: Lifeless, virgin planets will not be teeming with free oxygen for us to breath.

[Vexer]

Thanks for the replies, good people.