Category Archives: exoplanets

Abiotic Production of Oxygen/Ozone

Planets with carbon dioxide rich atmospheres won’t produce oxygen or ozone is amounts large enough to look misleadingly like an Earth-like planet…

Abiotic formation of O2 and O3 in high-CO2 terrestrial atmospheres

…but only if they have oceans. If the planet is frozen or a desert then the geochemical sinks for O2/3 produced by photolysis of CO2 won’t be working and they can build up. Thus signs of water, mild temperatures and oxygen means an oxygenic biosphere, not funny chemistry.

Except… Venus during its runaway greenhouse phase probably lost an ocean of water and had a very thick oxygen atmosphere as a result – but did that show? Scalding oceans covered in cloud, to an astronomer looking at its very cold cloud-tops (250 K) it probably looked like an “icehouse” and not a nice “Pale Blue Dot”.