Horizon joins the hunt for “second Earth” and considers whether there could be other habitable planets in the galaxy capable of supporting life.

Up until 12 years ago, astronomers had not seen any planets other than those in our solar system. Astronomers, however, are now at a point where they are finding new planets that may be just like Earth.

In Chile, the programme visits the world’s most sensitive planet detector. It is run by the Swiss team who found Gliese 581 c, the first Earth-sized planet that lies in “the habitable zone” around its star.

In Colorado, Nasa’s Kepler space telescope is being built. In 2009, it will embark on a four-year mission, seeking out new planets and telling scientists just how common Earth-like ones are in the galaxy.

Meanwhile, in northern California, The Search for Extraterrestrial Intelligence (SETI) continues. The team at SETI is listening for a message from the stars. This list of new planets is giving them fresh hope, as they expect Kelper to make them more effective in their scanning of the airwaves.

Horizon meets the SETI man who started it all, Frank Drake. His famous equation allows people to estimate how many intelligent ET planets there are in the galaxy. When he first defined it, humans had never seen a planet outside the Solar System. Today, many argue, we are closer than ever to finding not just second Earth, but also second life in the stars.

Tuesday 4 March
9.00-9.50pm BBC TWO