JOAN CARTAN-HANSEN, HOST: Exoplanets or extra-solar planets are planets that orbit stars outside our solar system.

So, what have scientists found deep in space?

Let's find out.

(MUSIC) JOAN CARTAN-HANSEN, HOST: A planet is a large body orbiting a star like our own sun.

There are eight planets and five dwarf planets including Pluto in our solar system.

Our Earth is the third planet from the sun.

But what lies beyond our solar system?

Are there other planets out there?

And if there are, is there life on any of those planets?

Planets that orbit around stars outside our solar system are called exoplanets or extra solar planets.

Scientists found the first exoplanet that orbited a sun like star in 1995.

That planet was named 51 Pegasi.

Since then, they have found thousands more.

Scientists now think planets may orbit around almost every star in the night sky.

But finding exoplanets isn't easy.

Planets are very small compared to the stars they orbit.

For example, the earth is ten billion times fainter than the sun.

So, scientists use lots of tools to look for exoplanets: computers, telescopes on the ground and telescopes in space.

Some exoplanet scientists look for very slight changes in the brightness of stars.

A star's light dims slightly when a planet passes in front of it.

Astronomers measure these tiny wobbles of the light from a star against stars in the background to find a planet.

Others use special telescopes that block out the light from a central star and take pictures looking for planets.

And using special tools, scientists are discovering what kind of elements are found on these exoplanets.

They are looking for things like water.

Scientists think that one in ten sun-like stars have Earth-sized planets that orbit in a zone where life could exist.

That area is called a habitable zone.

It's called that because, like Earth, it is not too close to the star which would make it too hot for life or not too far away from the sun would make it too cold.

One exoplanet, Gliese 581g, is about 20 light years away from Earth.

Its orbit around its sun is in the habitable zone.

Scientists are also very interested in looking at the atmospheres of exoplanets.

Earth's atmosphere has things like oxygen, water vapor, and methane.

Those things are there because plants create oxygen, large bodies of water give off water vapor and cows and other livestock fart and burp methane.

Knowing what is in an atmosphere is an indication of what life could be found on a planet.

And some scientists are even look in places where planets are just forming.

It's all a lot of work.

There could be billions of Earth-sized planets in our galaxy alone.

So, the search is on.

If you want to learn more about exoplanets, check out the Science Trek website.

You'll find it at ScienceTrek.org.]

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