He has made similar claims before that didn't pan out. Why is it risking his career if he truly believes it? It may just be a case of seeing what he wants to see.
Because NASA is a big government bureaucracy, and he's been working there since 1966.
Instead of thinking that there's got to be some truth to it, think that when there's a whiff of BS and it looks like the work of a bunch of delusional cranks publishing in their own vanity journal, it's nonsense and should be ignored.
Strangely, it's not just him, though I agree it doesn't seem particularly likely to be true. The journal's editorial board seems to have people who do reasonably respectable work when it comes to their work that doesn't involve panspermia. The journal's editor-in-chief, for example, is a well-respected director at Harvard's observatory, and his "normal" papers (reporting on finds via the telescope) get published in normal journals.
It is pretty strange that there are so many big names playing along. On the other hand, there's quite a long tradition of eminent, tenured, (and often aging) scientists going a little bit off the deep end, especially in areas outside of their actual expertise.
People say things for all kinds of weird reasons, which may range from pet theories to hawking books and getting speaking gigs.
> On the other hand, there's quite a long tradition of
> eminent, tenured, (and often aging) scientists going a
> little bit off the deep end, especially in areas outside
> of their actual expertise.
>Because NASA is a big government bureaucracy, and he's been working there since 1966.
To be fair, any other academic institution would have given him tenure. The point of tenure in those systems is precisely so that faculty can say batshit insane ideas with the hope that the odd lunatic will be right, or at least invite discussion.
Why would he risk his career and put his reputation at stake?