Upsilon Andromedae

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The constellation Andromeda stands high overhead this evening. It's best known as the home of the Andromeda galaxy, a great cosmic pinwheel that's about two and a half million light-years away.

But one of Andromeda's other points of interest is much closer to home. It's the first Sun-like star beyond our solar system found to have more than one planet.

The star is Upsilon Andromedae. It's a yellow-white star that's a little hotter and brighter than the Sun. Under dark skies, it's just visible to the unaided eye.

Astronomers discovered three planets in orbit around Upsilon Andromedae by measuring their gravitational pull on the star. They make the star move slightly toward and away from us, producing tiny "wiggles" in the star's light.

All three planets are giants, like Jupiter, the biggest planet in our own solar system. But all three are much closer to Upsilon Andromedae than Jupiter is to the Sun. In fact, the innermost world is closer even than Mercury, the closest planet to the Sun.

The second planet in the system is a little farther out -- perhaps far enough for the temperature to be right for liquid water -- an essential ingredient for life. Because it's probably a big ball of gas, the planet itself isn't a likely home for life. But if it has moons, they could be more hospitable.

Look for Andromeda soaring overhead this evening -- a constellation with a planetary system that's a little like home.

Script by Ken Croswell, Copyright 2008

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