Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected]. Are there any planets outside of our solar system? – Eli W., age 8, Baton Rouge, Louisiana This is a question that human beings have wondered about for thousands of years. Here’s how the ancient Greek mathematician Metrodorus (400-350 B.C.) put it: A universe where Earth is “the only world,” he said, is about as believable as a “large field containing a single stalk.” About 2,000 years later, in the 16th century, the Italian philosopher…

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