I think there was a HN thread not that long ago about speculation that (at least some) viruses come to earth from space, so perhaps it is happening all the time.
This seems such a "flat earth" type of hypothesis. I mean viruses depend on their hosts 100% so them coming from somewhere with no hosts and successfully slotting in with new hosts just seems immeasurably unlikely.
I think it makes more sense if you think of a virus as a software update for a genome. The question is not how a virus made it here--fashioning a delivery mechanism should be easy for a civilization advanced enough to hack into the genetics of a species on a distant planet--but who are it's authors and what new features or bug fixes does it provide?
Flu-like symptoms are probably just an unfortunate side effect. Things break during updates, it's an unfortunate fact of life. Maybe when a critical mass of people accept the update, they'll start building a giant transmitter for FRB's to let the sender know that the update was accepted.
I'm sure others have written more, and more intelligent things, but my general thinking about panspermia is:
- it seems like a universal rule there are more small things than large things
- there are more small red stars than stars like our sun
- there should probably be more brown dwarfs than small stars
- there are more small planets than large ones
- planets can and do form without stars
- planets should outnumber stars, and planets without stars should outnumber planets with stars
- there are probably more oceans below the surface of objects in our solar system than on the surface
- the universe existed for a long time before the solar system
...so it kind of seems intuitive to me that life should have developed underground where there's warmth from radioactivity and water, on countless free floating planets over billions of years and occasionally one of those gets blown to bits and something like that seeded our unusual planet.
...and it doesn't seem entirely implausible to me that there should be so much biological material in space that we get a certain amount all the time like micrometeoroids.