An appropriate question might be – is panspermia a “good” scientific theory? We need to address this in view of common disregard of panspermia by scientists and science commentators outside astrobiology. In comparison, let’s consider the status they accord to “string theory”.
String “theory” is a collection of concepts, with no empirical basis. It assumes space (or space-time) has many dimensions, the extra dimensions crling up but also ‘leaking’ to the ordinary space dimensions. Surely this is questionable and is characterisable as pseudoscience, practised by an in-group of believers.
In contrast, panspermia over many decades has made predictions and stimulated experimental checks, evolving from a hypothesis into a coherent theory. It’s pretty secure in terms of transfer of life between solar system bodies, though not (yet) for interstellar transfer.
Time for philosophers of science to say why panspermia has low status within the wider science establishment – called ‘controversial’ even by bioastronomer Caleb Sharf – while eg. string ‘theory’ is taken seriously.