[Lio]

What always blows my mind is that these most alien looking creatures are not alien at all. We share DNA with them and are evolved for the same planet.

Which begs the question, what would actual aliens look like?

Would parallel evolution produce familiar looking creatures or something much much stranger? I imagine it's something that sci-fi authors spend a bit of time thinking about.

[ecdavis]

There's a great book about this called "Life Beyond Earth" by Gerald Feinberg and Robert Shapiro. It discusses possibilities ranging from silicon-based life to plasma-based and even radiation-based life. It's not speculative, but since it's rather old the science in it may be dated.

It's worth reading if you're interested in this topic.

[dave_sullivan]

I'd also recommend Greg Egan's diaspora, it presents some interesting ideas around forms alien species might take. I don't want to give anything away, but the author takes things a few steps further than most sci-fi about exploring the universe(s).