Every star in our galaxy has at least one planet orbiting it, according to a new study, which suggests that alien planets are far more common than we thought.
An international team of astronomers led by Arnaud Cassan of the Paris Institute of Astrophysics used a new technique to search for planets. The astronomers say the new technique gives a more comprehensive picture than traditional methods. Their findings suggest that "planets are at least as numerous as the stars in the Milky Way."
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The data suggests that each star hosts at least 1.6 planets. There are at least 100 billion stars in our galaxy, according to Space.com, which means that we probably share it with more than 160 billion alien planets.
That estimate is a massive increase on the 700 planets astronomers have so far identified outside our solar system.
Traditionally, scientists have used one of two techniques to hunt alien planets: transit photometry, which involves watching for tiny dips in a star's brightness that indicate when a planet is crossing in front of it; or radial velocity, where researchers look for wobbles in a star's movement caused by the gravitational pull of planets orbiting it.
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Cassan and his colleagues used a different method, gravitational microlensing, which they say is better at identifying planets that are far away from their stars. Using relatively small telescopes, they watched from Earth for stars to pass directly in front of each other. The nearer star's gravitational field will bend and magnify the light from the star behind it – and so will any planets orbiting around it.
The team studied 100 million stars using this method, the Wall Street Journal reported. Then they combined their findings with earlier surveys to create a statistical sample of stars and the planets that orbit them. That allowed them to calculate the overall likelihood of other stars hosting planets, which, they conclude, is "a rule, rather than the exception."
Furthermore, their figures suggest that most alien planets are a similar size to Earth. According to the BBC, there could be some 10 billion Earth-sized planets in our galaxy. Study co-author Daniel Kubas said:
"We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way."
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