I can’t think of any material that burns and is not either man made, nor was once alive. So without a fuel source I can’t think of how fire could exist elsewhere.
Stars are of course fusion not fire, and lightning strikes on other worlds can’t start any kind of a fire I can think of.
The fuel source isn’t the problem.
Lava produces flame. There are plenty of gases released from vents that will spontaneously oxidise on the surface. So any volcanically active planet can have fire.
The problem is oxygen. Without life, it’s probably impossible for a planet to have an atmosphere high enough in oxygen for fire to exist. And if there is life, fuel isn’t a problem.
So your limitation is oxygen, not fuel or ignition sources.
Lessee… do you think a sulfur deposit might burn, given an oxidizer and a heat source?
The Earth is unique in the solar system in having an oxidizing atmosphere (which is itself a product of life). Everywhere else in the solar system with an atmosphere has a reducing atmosphere (lots of hydrogen in those gas giants), or none at all. Places without any atmosphere tend to be reducing as well, do to the hydrogen plasma in solar wind. I think it’s pretty fair to say that within our solar system, Earth is the only place where fire occurs, at least as we usually think of it.
One always reads of astronomers’ estimates of how many Earth-like planets there must be out there in the universe somewhere (lots and lots), with the possibility of having evolved life forms as we understand “life”. So that is equivalent to an estimate that there are lots and lots of places out there in the universe somewhere that would have fire as we know it.
ETA: Other than that, there must be lots of places with oxygen, but it is so reactive that one would never find it in its uncombined atomic form unless there was somebody (like plants) dumping a lot of it into the atmosphere. But oxygen that is already combined with other atoms is nothing other than oxygen that has already participated in a combustion reaction. If you define “fire” to include all reactions in which oxygen combines with other stuff, then there must have been places where that happened, even if the oxygen is all used up now and it isn’t happening any more.
Technically, flame is just a runaway chemical reaction that excites gas vapors into emitting light. Oxygen is a good gas for this sort of reaction, but there are non-oxygen oxidizers (e.g. chlorine trifluoride).
But not any that are likely to form in large quantities under abiotic conditions.
I guess the general rule is: anything reactive enough with each other such that they might cause a flame will have already reacted before the concentration gets high enough to support fire.
Life is just this really big oddity that is capable of using sunlight to power unfavorable reactions at a fast enough rate that you can build up some pretty reactive compounds to fairly high concentrations on a geologically short time scale.
Europa has quite a bit of oxygen.
Not unless you’re either using a definition of “quite a bit” that includes “almost none”, or you’re counting the oxygen that’s already used up in water molecules.
Wouldn’t compounds containing oxygen (or asome other oxidizer) burn in a reducing atmosphere?
Well, no. You need uncombined oxygen to support combustion.
Yes, but chlorine and fluorine are much rarer in the universe than oxygen. The chlorine breathing aliens of 30s science fiction are biochemically plausible, but there’s no plausible physical way to get a planet with concentrations of chlorine high enough to sustain a chlorine based biosphere. Oxygen is the third most common element in the universe, chlorine is several orders of magnitude less common.
So any place that has concentrated chlorine is likely to have much higher concentrations of oxygen, so fuels that could plausibly burn in chlorine would burn in oxygen first.
And let’s restrict “fire” to reactions exothermic enough to produce light visible by the human eye. So iron rusting isn’t fire, even though it’s exothermic oxidation.
Hydrogen and carbon are plentiful and burn nicely; and all the water in the universe was at one time hydrogen and oxygen, suggesting that, at least in a broader sense, the hydrogen burned. The actual question seems to be what processes could allow for an oxidizing that doesn’t just run its course and then stops forever when either the fuel or the oxygen is used up.
Io? It doesn’t have much of an atmosphere to speak of, but lots and lots of molten rock.
But glowing red rocks and molten lava aren’t “on fire”, they’re just hot.
It’s hard for people to understand because we’ve evolved on a planet with free oxygen in the atmosphere, but elemental oxygen is a pretty rare phenomenon in the universe even though oxygen itself is extremely common. This is because oxygen is extremely reactive, so reactive that if you just leave oxygen sitting around next to some other elements, within short order you’ve got no more free oxygen, instead you’ve got oxidized chemical compounds. Leave oxygen next to carbon and pretty soon you’ve got carbon dioxide. Leave oxygen next to hydrogen and pretty soon you’ve got water. Leave oxygen next to nitrogen and pretty soon you’ve got nitrous oxide. Leave oxygen next to silicon and pretty soon you’ve got sand. Leave oxygen next to iron and pretty soon you’ve got rust.
The reason for this is that on Earth plants continuously dump oxygen into the atmosphere as a waste product of photosynthesis. Without photosynthesis pretty soon all the oxygen in the atmosphere would combine with other stuff and there would be no more oxygen in the atmosphere.
So remember your fire triangle. Fire requires fuel, oxidizer, and heat. Remove any of those and you don’t get fire. On planet earth there’s a nearly omnipresent source of oxidizer, the oxygen in the atmosphere. It’s so abundant that humans on earth have to have specially trained teams of people just sitting around ready to spring into action when as often happens one of their dwellings starts to spontaneously combine with the atmosphere. But almost all other places in the universe lack a supply of oxidizer. Or rather, whatever oxidizers there are have already oxidized to their lowest energy state.
In most cases this oxidation wasn’t “fire”, since it didn’t create hot clouds of gasses that emitted light that a naked human eye could have detected. There never was a gigantic fire on Earth as all the hydrogen in the atmosphere burned with all the oxygen in the atmosphere to create our oceans. The water on Earth probably arrived already combined. The iron in our crust didn’t burn into iron oxide, like you can burn steel wool, it just rusted into iron oxide without creating a fire. Even on Earth it takes very specific conditions to make a fire out of iron with oxygen. But leave your Buick out in the backyard for 300 years and you’ll come back to a pile of iron oxide, even though if you reviewed the webcam footage you’ll never see a fire.
Are we restricting this question to our own solar system, or is it really 'anywhere other than Earth" - because there must be other planets out there with oxygen-rich atmospheres, and things that will burn, and sources of ignition. The universe is just too damn huge for this to be the only place where it happens.
That’s right. And lava that is on fire isn’t just glowing red rocks and molten lava, it’s burning.
Which doesn’t happen on Io.
Several metals can burn, with a flame, if exposed to oxygen or water.
That is why our planet was such a puzzlement to ancient aliens. “Every time we try to colonize that planet, some of our houses turn to gas and heat, then disappear.”
