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Discovering Exoplanets
What Is an Exoplanet?
An exoplanet is a planet that is outside our solar system. Planets in our solar system orbit around the star we call the Sun. Exoplanets also orbit around a star. Some of the stars you see in the night sky might have exoplanets orbiting around them.
Have Any Exoplanets Been Discovered?
Astronomers are people who study stars and other objects in space. For a long time, astronomers could only guess about whether some stars had exoplanets orbiting around them. The technology needed to find exoplanets did not yet exist. But technology improved over time, and astronomers discovered the first exoplanet in 1992. Since then, astronomers have discovered hundreds of exoplanets.
How Do Astronomers Discover Exoplanets?
Astronomers have two different ways of discovering exoplanets. The first way is called the wobble method. Like Earth and other planets, exoplanets have gravity that pulls on things around them. The Moon does not fly off into space because Earth’s gravity pulls on it and keeps it close to Earth. Exoplanets also have gravity. An exoplanet’s gravity pulls on the star it orbits around. This causes the star to wobble—to shift position a tiny bit. Exoplanets are too small and too far away for astronomers to see with telescopes. But when astronomers see a star wobble, they know there must be an exoplanet pulling on it.
The second way astronomers discover exoplanets is called the transit method. The word transit can mean “to pass across.” Since an exoplanet orbits around a star, astronomers know that sometimes the exoplanet passes across the part of the star that they can see.
If exoplanets are too small and too far away for astronomers to see, how can they tell if an exoplanet is passing across a star? Astronomers can record how much light is coming from a star. When an exoplanet passes across a star, it blocks some of the light coming from the star, so the star appears slightly dimmer for a time. When astronomers see that a tiny bit less light is coming from a star, they have a clue that an exoplanet might be passing in front of it.
Astronomers then keep watching star. If the star grows slightly dimmer over and over again, they know that there must be an exoplanet orbiting around the star.
Is There Life on Exoplanets?
Astronomers have not yet seen any evidence of life on exoplanets. They are now looking for planets that might have the right conditions for life. Astronomers know that an exoplanet that orbits very close to a star is probably far too hot for life to exist. If an exoplanet orbits too far from a star, it is probably too cold for life. Astronomers are looking for exoplanets that are not too close to or too far from a star. Finding an exoplanet like this does not guarantee that there will be some form of life on it, but it would be a good place to start looking.
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