Planets--others in our solar system, gas giants, frozen planets, and many others--have long been a staple of science fiction. While these novel environments can evoke a sense of wonder, planets similar to ours could host something even more wonderful--life. When I was born, we hadn't found other planets outside our solar system. About fifteen years ago, the technology to find them became available, but at first, we could only find Jupiter-sized planets. Today, we've detected 150 Earth-sized planets, the kind most suitable for life as we know it. It's estimated there are 100 million planets similar to ours in our galaxy. For more details, check out this interview with astronomer Dimitar Sasselov on CNN.
If there really are so many other possibly habitable worlds out there, that should be good news for science fiction writers and explorers. The problem is our galaxy is so vast we couldn't visit these planets with our current technology, at least not in any reasonable time. This is why science fiction writers need to come up with some way of making faster-than-light (FTL) travel possible. For me, I use a wormhole; a spaceship can enter one end and pop out somewhere else.
One other interesting point in the article is how long life has been a part of the universe. According to Sasselov, it's been around (at least on Earth) for about a third of the universe's life. (We had to wait for other stars to create other elements besides hydrogen and helium.) With so many planets and so much time to work with, there can be all sorts of alien beings out there. Perhaps some are similar to those here on Earth, or perhaps there are worlds where the biology is just a little off. (For example, perhaps some lifeforms use the same chemicals as we do but different optical isomers of them.) Or perhaps some worlds have biology so bizarre it could have only been imagined by a science fiction writer.
Perhaps the planets aren't so lonely after all.