The following infographic is a comparison of three alien star systems with our own solar system. It shows the distance at which all the known planets orbit around their stars.
As of August 10, 2011, 573 extra-solar planets have been identified, but so far the three systems illustrated below are the record holders for having the most planets. [reference]
From this we can see that most discovered planets orbit too close to their stars to be able to support liquid water (and perhaps life). However two of them orbit within the so-called “Goldilocks zone” which means that they are not too hot and not too cold, but just right. Unfortunately planet HD 10180g is a Hot Neptune and thus could not support Earth-like life. As for the other planet, Gliese 581g it is a more promising candidate, but it is 3.1 times the mass of Earth and thus has a high surface gravity. It also orbits really close to its star, exposing it to high radiation levels. As the search for exoplanets continues, we may one day discover a planet that could potentially support Earth-like life.
Infographic source: Space.com