Is the alien theory a scientific claim? Why or why not?

I'm not sure what the alien Theory says or if there really is such a theory. If the theory says that aliens definitely exist and that they have visited Earth in the past then the theory is totally and completely without any kind of support. It's not scientific in any way because there is no evidence for such a claim. It may be thought to be probable but no solid evidence has ever been presented.

It is because the probability of more planets being able to hold life are likely. There are so many planets that many have to have the same conditions as earth which means they are able to hold life