Number 33 (Story #4), May 8, 1991 by Phillip F. Schewe and Ben Stein ALPHA CENTAURI , the Sun's nearest neighbor, seems to have many of the properties necessary for fostering life. Alpha Centauri A, the biggest of the three stars that make up the stellar system, is a lot like our local star: they are both classified as a G2-type star (neither too hot nor too cold for life). This criterion alone rules out most stars in our galaxy, including red dwarfs (70% of the stars in the Milky Way) and white dwarfs (10%). Alpha Centauri A is also, like our Sun, stable (it wouldn't fry and then freeze life), old enough (intelligent life took 4.6 billion years to evolve on Earth), and metal rich (metals, in this case meaning any element heavier than helium, are necessary for life.) The celestial mechanics of three Alpha Centauri stars is such that small rocky planets could form, but it is more difficult to say whether any of them would be warm and watery enough to support life. (Astronomy, April 1991.)