What a great time to ask about finding extrasolar planets -- planets orbiting stars outside our solar system!

On Friday, NASA just launch a special robotic spacecraft - the Kepler Mission (http://www.nasa.gov/mission_pages/kepler) - which will look for planets around other stars. It finds them by monitoring the light from the star and watching for a small dip in the brightness that is caused by the planet passing in front of the star, blocking out some of the light. And there's another European spacecraft up there searching, too. It is named Corot.

Two other techniques make use of the fact that in any planetary system, the star and all the planets actual orbit around the center of mass of the whole system. So if a star has a really heavy planet - such as Jupiter - the star actually oribits around the "center of mass" location. We can detect this little "wobble" in the stars motion.

Paulett

Hi Kendra! Extra-solar planets are an exciting subject, and new ones continue to be discovered. There are several methods for finding them. Most are found via the "radial velocity" method. This method takes advantage of the fact that the star will respond to the gravitational pull of the planet -- not very much, but enough to detected as a modulation in the star's spectrum. The star's response to the planet can also be observed via "astrometry" -- astronomers look for small wobbles in the stars position. Another way is "microlensing", where the presence of a planet will affect how light from its star is bent by the gravity of another star in front of it. Another way is "transit photometry" -- as the planet passes in front of the star, the star's brightness dims, just a bit. Finally, maybe the most visually satisfying, but unfortunately a quite difficult way of finding an extrasolar planet is to actually image it with a powerful telescope -- this has been done a few times, but only for very large/bright planets that are not too close to their stars. See http://www.planetary.org/.../search_methods.html for more details! cheers, Sarah