Artist's concept of a rocky planet in orbit around a distant star.
Click on image for full size
NASA, ESA and G. Bacon (STScI)

Planets around other Stars

Did you know that about 200 planets have been discovered in orbit around distant stars? The first planet found to be orbiting a star like our Sun was announced in 1995. Since then astronomers have continued to find new planets outside of our solar system, at a rate of more than one new planet every month!

The star and its planet orbit a common center of gravity. The planet moves in a wide orbit, while the star just appears to wobble slightly. By measuring the Doppler shift from the spectrum of the star, scientists can detect the tiny motion caused by the planet. Most of the distant planets were discovered using this technique.

If we are lucky enough to be lined up properly with the planet's orbit, it can occasionally pass in front of the star, blocking out some of the light that we usually see from the star and briefly making it appear dimmer. It's like a solar eclipse, but the planet only covers a small fraction of the star. Only a few of the planets outside of our solar system pass in front of their stars.

All of the distant planets are much too far away to resolve directly. We can only see their effect on the star that they orbit.

Last modified March 13, 2008 by Becca Hatheway.

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