I am very excited by the discovery of so many planets around other stars. That, to me, means that we have a better chance of finding life on another planet. Many of the planets discovered though are a lot like Jupiter and many orbit their sun in very close orbits, not a situation conducive to human life! For a planet to have a chance at supporting life as we know it, it must be at about the distance Earth is from our Sun, scientists call this the "Goldilocks Zone". That said, "life" can exist in very diverse and extreme environments. See this article: http://science1.nasa.gov/...03/02oct_goldilocks/

The way these exoplanets are discovered is to look for changes in the amount of light coming from the star itself. If you make a graph of the light from the star over time, called a "light curve", you might see a "dip" in the curve. That dip could be caused by starspots, another orbiting star, or an orbiting planet. Scientists have to rule out starspots and another star before making the claim of the discovery of a planet around the star, which they can do by detailed analysis of the light curve. To learn more about exoplanet discoveries, visit this site and take a look at the PlanetQuest timeline: http://planetquest.jpl.nasa.gov/interactives

I think the quest to find extra-solar planets is amazing - and partly because of what can be learned about the stars, and how stars formed, along the way. As Mitzi said, looking at the changes in the light helps figure out if what's making the star's light dim is a planet or a "star-spot". From the posts and information on sunspots, you know that these spots are the locations of strong magnetic fields. These magnetic fields also change the light coming from the star, so one of the ways to rule out the dips as being due to star-spots is to see if there are indications of magnetic fields. And in doing so, we learn about the star itself!

Also, learning about how many Jupiter-type planets vs. Earth-type planets, and where they are (how far away from the star do they orbit?), and around what kind of stars, tells us about how stars and planetary systems formed in the first place. Are we 'weird' to have rocky Earth-like planets? Are massive close-in orbiting Jupiter-sized things more normal than what we have? Do only certain kinds of stars have certain kinds of planets? These are all questions that we can really start asking now! (And, even if the answers to those questions create other questions, well, that's science. :-)