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The solar system KOI-691, shown in the above rendering, features the three smallest exoplanets known to orbit a star other than our sun. (NASA / JPL-Caltech)

Faraway Worlds

Scientists scan outer space for planets beyond our solar system

<p>Astrophysicist Ben Oppenheimer (Courtesy of the American Museum of Natural History)</p>

Astrophysicist Ben Oppenheimer (Courtesy of the American Museum of Natural History)

As a boy, Ben Oppenheimer always loved looking at the night sky. He wondered what secrets the stars held. Are they circled by planets, alien-populated worlds, or distant moons?

Today, Oppenheimer has the tools to find out. He is an astrophysicist at the American Museum of Natural History in New York. He studies exoplanets, planets that orbit stars other than the sun. So far scientists at observatories around the world have confirmed the presence of more than 900 planets circling around other stars in our galaxy. There are probably thousands more.

Scientists knew little about these other worlds, other than that they existed. Now, Oppenheimer and his team have found a way to see what these planets are like. In time, they may even be able to identify which of them support life.


Astronomers can learn about exoplanets by looking at their light. Planets don't shine brightly, the way stars do. Instead, planets give off heat energy called infrared light. Our eyes can't see it. But telescopes can collect this light to make an image for astronomers to look at.

A planet's light would be easy to study if everything nearby were dark. But that’s not the case. Blindingly bright starlight makes it difficult to see a planet.

To solve this problem, astronomers developed telescopes that could block a star’s harsh light. “Think about having a bright light shining in your face,” Oppenheimer says. “If you hold your hand up to block the light, you can see better.”

Oppenheimer’s exoplanet-finding telescope works the same way. It uses a small piece of metal to cover up a star. Then he and his colleagues can see the light from any nearby planets. The team is scanning 200 different stars with this technique. “The hope is that we'll see a bunch of new planets,” says Oppenheimer.


Oppenheimer doesn’t just want to find exoplanets, though. He wants to know all about them. What are they made of? What’s the weather like? Could there be life there? For the first time, scientists are learning the answers to these questions.

Astronomers can use a planet's light to determine which types of gases make up its atmosphere. That’s because different molecules absorb different colors of light. Knowing the atmosphere’s composition helps scientists understand how the planets formed and what their weather might be like. Are they gas giants like Jupiter, or rocky worlds like Earth?

Oppenheimer recently used this method to study four exoplanets orbiting a single star. He found that their atmospheres contain water vapor, methane, and ammonia. That means the planets are gaseous and warm—unlike any planets in our own solar system.

Someday astronomers may use this technique to find signs of alien life on an exoplanet. On Earth, plants release oxygen into the atmosphere. Animals and other living things give off carbon dioxide. If scientists find a planet with an atmosphere like ours, it might be a clue that something there is alive.

Check It Out

To see exoplanets through a telescope, scientists block out bright starlight by attaching a device called a coronagraph. In the American Museum of Natural History’s Dorothy and Lewis B. Cullman Hall of the Universe, you can see the coronagraph that scientists used to discover a star-like object called a brown dwarf. You can also check out beautiful images of faraway galaxies, a 15.5-ton meteorite, and scales that tell you what your weight would be on Mars, Jupiter, and the sun. To learn more, go to

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