Gliese 876

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The southern sky of autumn features one of the faintest constellations of the zodiac: Aquarius, the water bearer. It's home to a faint but famous star, known as Gliese 876. It was the first red-dwarf star found to have planets.

Gliese 876 is too faint to see without a telescope. But at just 15 light-years, it's one of our nearest neighbors. American astronomer Frank Ross discovered the star in the 1920s. And in the late 1990s, astronomers first discovered planets orbiting the star.

These planets are important, because red dwarfs are the most common type of star in the galaxy. In fact, they outnumber all other types of stars put together. So if red dwarfs can have planets, then the galaxy may abound with planets.

So far, astronomers have discovered three planets orbiting Gliese 876. Two of them are in a two-to-one resonance: One planet takes a month to complete an orbit, while the other takes two months.

As a red dwarf, Gliese 876 is far less massive than the Sun. So astronomers expected its planets to be less massive than the planets of our own solar system. But strangely enough, that's not the case: the two resonant planets are about as massive as Jupiter, the giant of our solar system.

So the planets of Gliese 876 were not only the first to show that red dwarfs can have planets, just as brighter stars do -- they were also the first to show that small stars can have big planets, as mighty as any that orbit the Sun.

Script by Ken Croswell, Copyright 2008

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