astronomers have developed some very clever techniques for indirectly detecting planets. They can look for a small wiggle in a star’s position, which means that the star is being pulled slightly by the gravitational force of a planet. They can also look for periodic dips in the light from the star, which means that the planet orbiting the star is passing in front of it. Using these techniques and others, astronomers have discovered something incredible: about one in five stars in our galaxy has a rocky planet with a size similar to Earth’s and a similar amount of solar energy on its surface.
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