Two Planets Found Orbiting One Star

Two Planets Found Orbiting One Star

By jeffa

8/27/2010

Artist's idea of what this two planet system might look like courtesy NASA/Ames/JPL-Caltech
Artist conception of two planets orbiting one star

When you look into the sky at night you see lots of stars, right? You also see a few planets that orbit the sun. Planets like Mars and Venus.

When you look at stars, you can't see if they have planets orbiting them can you? No, you can't because they are SO far away that even the super gigantic stars look like little dots of light. 

If you use binoculars or even a telescope you still just see little dots of light.

Planets are MUCH smaller than stars, so there is NO chance you can see them.

Until about 20 years ago there was simply no way to tell if a star had planets.

The first planets detected weren't seen, but the effect they had on their stars was detected.

Imagine if you had a heavy ball on the end of a rope and you swung it around and around. It would tug at you and keep you from spinning in one spot. You'd wiggle around a little, wouldn't you?

The same is true of a star with a planet. As the planet goes around the star the gravity makes the planet tug at the star just like the rope and ball would tug at you. That makes the star waggle around a little. Even if you can't see the tiny little planets, you can see the star waggle!

That was the first way people detected planets, but then someone had another idea!

If the planet is big enough and your telescope is good enough, you might be able to see the amount of light coming from the star dim just a little when the planet goes between the star and you. 

One REALLY big problem with telescopes on earth is that they all have to look up through the atmosphere to see stars. That's almost like looking through the water in a swimming pool at something on the bottom. It looks like it is moving when it isn't! The waves and ripples in the water make it hard to see something small. The same is true of the atmosphere.

If a telescope is put into space where there is no atmosphere, it doesn't have this problem.

The Kepler space telescope is just that kind of telescope! It's main mission is to find planets the size of earth around other stars.

Kepler spacecraft image courtesy NASA/Ames/JPL-Caltech

Kepler Spacecraft

Several planets have been found using this method, but now the Kepler spacecraft has found two planets for the first time!

Even though we can't directly see the planets, we can make several good guesses based on what we do see. Scientists believe that the two planets are almost as big as the planet Saturn. The one closest to the star goes around the star in just 19 days! That just over two weeks here on earth! It takes earth 365 days to go around our sun! The second planet is farther from the star, but still only takes about 38 days.

Scientists aren't completely sure, but they think they may see signs of a third, smaller planet!

You can read more about this discovery at the NASA website here.