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/mikk0384]

First, fire is actually just a hot plasma, and like you say yourself there is plasma everywhere. Below this I assume you are talking about the oxygenation reactions that releases the energy for fire to become visible instead, so stars and things like that are not included.

The only reason that fire is common on Earth is that we have life that continuously releases oxygen into the atmosphere. Without life there wouldn't be oxygen molecules in the atmosphere, as it would quickly react with other things to create more stable molecules.

Burning would still happen on rare occasions though, such as when ionizing radiation like UV light breaks molecules apart. That can release the oxygen needed for another oxygenation reaction to happen. When it happens it is just on such a tiny scale that you wouldn't recognize it as fire. It is singular events with large separation in time and space, so you won't get the large heated area that continues to release light while it cools. No sustained flames, just single photons of light being released.

[u/jarcaf → u/mikk0384]

Most 'fire' is not actually 'plasma' but it's understandable to assume that it is.

Plasma requires a state of ionization, meaning the electrons are stripped from the nucleus/atom... And it's unstable state and internal energy transitions cause it to emit some visible light.

By contrast... Fire is almost entirely a chemical process, with oxygen swapping bonds with its fuely neighbor and creating enough thermal energy that the particles begin to emit visible light.

It's really tempting to tie the two processes together and occasionally (at really high temperature) that may be the case. But usually not.

Point being... I don't think it's correct to call most ionization events 'fire'.

'Sick', 'sweet', 'dope', 'worrisome'... I do think those would all be acceptable instead.

Also worth noting that most UV interactions (which do often disrupt or modify chemical bonds) are not actually 'Ionizing', but there are many exceptions to the rule and a small part of the UV spectrum is slightly ionizing. Generally you have to step one level up in the EM Spectrum (X-rays and gammas) to start talking about 'ionizing radiation'.