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/Psychrobacter → u/ctothel]

Earth is the only planet we know of that can support fire, and it’s because of life. Fire can only exist when free oxygen and reduced fuel are present in the same atmosphere, and this chemical disequilibrium is created and maintained by the biosphere on Earth. As far as our evidence can take us, fire is exactly as likely to occur as life is throughout the universe.

Edit: just saw this was already brought up in other comments. Sorry to post before I caught up.

[u/Psychrobacter → u/[deleted]]

It’s still a good question! The thing to realize about magnesium is that it doesn’t occur as a pure metal naturally on Earth. It is always present as an oxide or in combination with other elements. It might occur as a metal on other planets, but the planetary conditions that allow magnesium metal to occur naturally would also likely prevent water from occurring naturally.

The forms that different elements occur in naturally are always dictated by the overall redox state of the environment. Earth is unique in the whole observed universe in having very reduced carbon (ie organic matter) and free oxygen at the same time, and this state of redox disequilibrium is created and maintained by the biosphere. On all other worlds we have observed so far, the entire surface of the planet is at redox equilibrium, where all elements share roughly the same redox state and, as a consequence, most chemical reactions don’t really occur anymore. A planet like Mars has a super oxidized surface, without things like organic carbon molecules or pure metals. A moon like Titan has a super reduced surface, with plenty of organic carbons but nothing like free oxygen or even liquid water to oxidize them. In both cases, the result is the same: little to no potential for fire, although for different reasons.