Is there life elsewhere in the Universe? Until just recently, scientists didn't even know if there were planets beyond our own solar system, much less habitable ones. But, in the last decade, astronomers have found more than 30 of these extrasolar planets by looking for the slight gravitational wobble they induce in their parent stars.

At the Harvard-Smithsonian Center for Astrophysics, David Latham and his colleagues are pioneering a more direct method of extrasolar planet detection. In "Alien Worlds," Latham's team looks for stars that dim periodically, indicating the transit of a planet between the star and Earth-bound observers. The amount of light blocked reveals the diameter of the planet. The frequency of the dimming provides the planet's orbit.

As revealing as this technique is, it requires a lot of patience. As Latham tells Alan Alda, "you have to look at a lot of stars to see the ones that are lined up just right to see a transit." The researchers' perseverance has paid off. After seven years of work, Latham's team has just made the first ever observation of an extrasolar planet passing in front of a distant star.

		The powerful Keck Telescope, high atop a Hawaiian volcano

Some researchers aren't waiting to find a planet. Paul Horowitz is working under the assumption intelligent life is already out there- and looking for us. Horowitz scans the skies for regular flashes of light; possible signals from one intelligent civilization to another. Everyone acknowledges it's a longshot, but it's just one more creative attempt at answering the question, "Are we alone?"

For more on this topic, see the web feature:
Is Anybody Out There?