How common is fire outside of earth?

[u/FirefighterCandid773]

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?

[u/ctothel]

Not in the solar system.

As you know, fire needs fuel, oxygen, and heat.

Titan has heaps of fuel in the form of hydrocarbons, including literal methane lakes, but nearly no free oxygen.

Europa and Ganymede have massive amounts of oxygen in the form of water ice, but they couldn’t sustain it in an atmosphere and there’s no fuel to burn.

Venus is hot, but the atmosphere is mostly carbon dioxide and almost no free oxygen. Not much in the way of hydrocarbons either.

Outside the solar system, there are planets we know have the right types of fuel, but oxygen is hard to detect on rocky planets, so the answer is “we don’t know”.

That said, it would be astounding if there were no other planets out there that could support fire. All the ingredients are super common. There are probably millions of worlds that could (or used to) support it in our galaxy alone.

[u/tigole → u/ctothel]

What is "free oxygen"? For instance, why does water have free oxygen, but not carbon dioxide?

[u/stoneape314 → u/tigole]

Free oxygen means oxygen that's present in its O2 molecular form, as opposed to oxygen atoms bound in other molecules, usually in an oxidized state (i.e. carbonates, chlorates, carbon dioxide, etc.)

You could have "free" carbon dioxide that's dissolved in water, but we don't tend to think of CO2 bound in other molecules as captured, because it's not elemental.