Biologically speaking, can unearthly anatomy be possible? Natural sciences are partly comprised of theories, so the idea that there could be extraterrestrial life seems more than possible.
I don’t think that imagination can be used by itself to support the possibility of extraterrestrial life, but in conjunction with ways of knowing like reason or intuition there is a much more stronger support of the possibility.
Unexplained historic findings, dating back to before the common era, still have many people baffled. Some historic feats have been accomplished using technology that is far beyond their time. Historic works, such as “The Madonna with Saint Giovanni” painting, have included peculiar subjects that can only be determined as unearthly/unexplained.
The ways in which indigenous knowledge systems are used to support this possibility is partially by alien sightings. Many people have claimed to have seen alien spacecraft or even to have been abducted by aliens. While not everyone who claims to have experience these occurrences can be cited as a reliable source, the sheer amount of claims in itself should reveal that there is something going on behind the veil.
Astronomer Frank Drake determined an equation to figure out the likelihood of other life existing. Statically speaking, hundreds of thousands of planets with the potential to have life exist.