During the past 12 months, astronomers have finally discovered planets orbiting Sun-like stars. All were discovered by precise Doppler measurements of the host stars. Some of these planets have properties similar to the nine planets in our own Solar System. But many of the planets have properties that are totally unexpected.
Several of the planets are more massive than even Jupiter and some orbit their host star in very small orbits, smaller than Mercury's orbit. Equally unexpected is that two of these "planets" have non-circular orbits.
Current theory of the formation of planetary systems is suddenly challenged to account for these new planetary properties. The character of the new worlds spawns many questions about the uniqueness of our Solar System and the prevalence of Earth-like planets.
These questions are now being addressed with the Keck 10-meter telescope, which will hunt for Saturn-like and Neptune-like planets.