What we know about the innumerable planets outside of our solar system

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 curiouskidsus@theconversation.com. 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 bel