Maybe there is a pink banana-shaped flying monkey who can breathe fire and fly faster than the speed of sound. But nobody has such an opinion, so why would it even come up?
Over here, though, there are people who have opinions, and there is the source in shoftim, perek 5, passuk 23, where Rashi explains that one opinion is that this was a star. And the inhabitants of the star didn’t come to help in battle.
On the other side, this seems hard to understand because why specifically here should they have come? Why not when bnei yisrael were attacked by amalek, or when yehoshua conquered erets yisrael, or any other wars?
The general view probably follows the second opinion which Rashi says, this was a distinguished person who was near the battle field but failed to appear.
But, it still shows that there is and was an idea out there even by Rashi, that there could be other living beings on a different planet too. yes, it’s farfetched, & I don’t know if there is, but it’s totally possible!