If you had to look for alien planets, where would you look? The galaxy has one hundred billion stars -- if you could look at one every second, it would take 3200 years to search them all. The problem is, NASA is planning a planet search mission called the Terrestrial Planet Finder. This series of satellites will need much more than one second per star, and may only get to look at a few thousand stars during its lifetime. So, which thousand should we look at?
A report by astronomer Margaret Turnbull lists nearly 150 stars that might be worth checking out. The stars on this list are chosen to be nearby (within 100 light-years of Earth) and to be fairly similar to the sun -- old stars with about the same amount of metals as the sun, about the same temperature and mass as the sun, and without any companion stars.
It makes sense to start the search for Earth-like planets with Sun-like stars. After all, all four known rocky planets are around our Sun! So we know that Sun-like stars can have Earth-like planets. Maybe other stars can have Earth-like planets, too, but it is a riskier proposition.
Since the mission launch is not for at least ten years, this list will be debated, revised and expanded until launch. But perhaps in ten years we'll know where E.T. calls home.