I looked through a high-power telescope for the first time in college. I couldn’t believe how many stars I saw. It’s hard to imagine all the planets orbiting all those stars.

I talked about how we know those planets are out there with my friend Jose Vazquez. He’s an astronomer at Washington State University.

He told me that scientists look for planets outside our solar system using a number of instruments—like a photometer. That’s a tool that attaches to a telescope and measures light.

The sun and eight major planets make up our solar system. All the planets outside our solar system are called extrasolar planets or exoplanets. Some of them are called hot Jupiters. Exoplanets orbit other stars—just like we orbit the sun.

The closest exoplanet is nearly 25 trillion miles away. Scientists can’t point a telescope and look directly at a planet that distant. They can’t send a rover that far. Instead, they look for clues that a planet is there.

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