Is Earth the only living needle in this haystack of planets?

We live in one of a hundred billion of galaxies, each with hundreds of billions of stars. And now, thanks to modern astronomy, we know that the Milky Way is home to perhaps a hundred billion planets! In the past two decades, these exoplanet discoveries have spawned new questions about our universe, and if there might be another Earth, or other life, somewhere out there.

In part 1 of my two-part series on exoplanets, we’ll look at how astronomers find exoplanets, and what it means to call them Earth-like. We’ll trace the history of planetary science back three thousand years and examine Earth’s changing status in the cosmos. We were once the center of the universe, and now Earth is just another rock in the sky. What does that mean for us?


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