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What is an exoplanet? An exoplanet is basically any planet that is found outside the solar system. For the longest time astronomers thought that planets only occurred in our solar system and even when planets were discovered orbiting other stars that there were not any that had the same mass or orbit as Earths. However new instrumentation and observation methods are proving this to be a false assumption.
First how have we been able to detect planets outside our solar system? Planets if we use the practical example of our own solar system are normally several orders smaller than their stars. Since they also don’t emit light they are basically invisible to traditional telescopes. The way we have found exoplanets is by math and observing the movements of stars. A star with planets and a star without them will move differently because the subtle influence of each planet’s gravity. While not having a gravitational field as strong as that of a star collectively the planets of a star system do exert a pull on their respective stars. It was using a similar method observing the movements of the outer planets that we found the remaining nine planetary objects in our solar system.
In the case of stars spectroscopy is the method that was used spectroscopy and radial velocity. Since planets exert a collective pull on their stars the stars end up moving in their own smaller orbit. This movement causes a shift in the frequency of the light they emit due to the Doppler Effect. With the help o f spectroscopy and some math scientist can find out if the movement of a star is influenced by planets.
Another method of detecting exoplanets is observing changes in their brightness. It makes sense that when a planet passes between a distant star and an observer on earth the brightness will lessen momentarily. NASA launched a telescope that can measure this change in brightness and use it to calculate the orbit of the planet as well as its mass.
The last method of detection is old fashioned radio telescope images. By detecting the radiation emitted by distant celestial bodies scientist have also been able to find planets. The growing consensus is that there are many more exoplanets in the universe than previously expected there may be a lot more because the limitations of observations from Earth. This means interesting thing for whether there is life on Earth. It used to be thought that Earth only had the right set of conditions for life to be possible. However, there are more stars out there with planets the odds of another planet with the ability to bear life being out there becomes more possible than ever before.
We’ve also recorded an entire episode of Astronomy Cast all about Exoplanets. Listen here, Episode 34: Discovering Another Planet.
Sources: Wikipedia, NASA