With viruses being such a point of contention amongst biologists, I always wondered how the discovery of alien "life" would challenge our current definitions.
I always imagined alien life as something completely different then anything we have on Earth, not made of cells or even DNA as we know it, but rather made up of their own self-replicating structures. Of course I use the term "imagine" loosely because it'd be impossible to tell what such creatures look like - there's a reason most pop culture depictions of aliens are just anthropomorphised or monster-fied versions of creatures we've seen on Earth.
But eh I'm no real scientist, and I doubt we'll ever see aliens within my life time. I just think its a neat topic to think about.