Smaller extra-Solar System planets

A newspaper article today reported that several planets of a size similar to those of Uranus and Neptune have now been found to orbit stars outside our solar system. Previously, only Saturn size planets had been detected.

For some reason, I am fascinated by the idea of planets orbiting stars outside our system. Planets discovered so far tend to be to big, and to orbit too closely to their parent stars, to be able to support organic life, but it is predicted that we will eventually be able to detect earth-sized planets.

One astronomer predicts that the Milky Way contains as many as two billion planets. I have no idea of the merits of this claim, but if this figure is true, I wish I owned a dollar for each one!