Question: Are some planets dangerous?

Michael Schubert answered on 13 Mar 2020:

Most of the planets we know about are very dangerous to humans. We couldn’t survive unprotected on any of them, and even with protection, we couldn’t survive for very long.

There is a category of Earth-like planets that might be safe for humans to live on, but we won’t know for sure until we are able to reach them and study them more closely. Unfortunately, they are much too far away for our current space travel technology. We’ll need to get much better and faster at space travel before we can start looking for planets we could safely live on.

That doesn’t mean there couldn’t be life on planets that are unsafe for humans. It just means that life on those planets would have to be adapted to those environments, which would mean it would look very different to humans!