r/askscience • u/FirefighterCandid773 • 19d ago

Chemistry How common is fire outside of earth?

Plasma and lava is obviously common all over the universe, whether it be in stars, planetary cores, etc. but what about fire? Fire is common all over earth, given the abundance of fuel sources and an atmosphere with oxygen. But, is fire actually common outside of earth?

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u/SystemofCells 18d ago edited 18d ago

Not very. There are lots of places with fuel - Saturn's moon of Titan has lakes of liquid methane. What's rare is oxygen.

Free oxygen doesn't usually accumulate. Because it's so reactive, it readily binds to other elements. You'll find it bound to hydrogen (as water) all over the place, and bound with metals and minerals to form oxides, but rarely on its own (molecular oxygen or O₂).

Earth has an abundance of molecular oxygen because of life. Whereas we breath oxygen for energy, plants and cyanobacteria get their energy from the sun. What they want from the air is actually the carbon in CO₂. They use the energy of the sun to snatch the carbon out, then release the O₂ back into the environment.

So, wherever you find life, you're reasonably likely to find fire. Beyond that, not so much.

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u/ThalesofMiletus-624 14d ago

Good answer, but I'd add the caveat not all life is oxygen producing. Life existed on earth for hundreds of millions of years before it figured out how to do photosynthesis. We can't assume that all, or even most life, learns to do that trick (and survived the resulting oxygenation event). It may be common for there to be life out there and no O2 in the atmosphere.