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October 22, 1975. After traveling millions of miles through space, a Soviet spacecraft plunges through thick clouds of sulfuric acid to land on Venus. Its goal: take a photograph of another planet’s surface and send it back home—history’s first up-close glimpse at a world other than our own. Venus, our closest neighbor, is similar in size to Earth and may even share some planetary material. It’s why scientists sometimes call it our twin planet. Yet its rock-melting temperatures and poisonous atmosphere make it profoundly different. If anything, it is our evil twin. What’s behind humanity's long fascination with Venus? And what can the differences between these cosmic twins teach us about our home planet…its present, and its possible future?

Special thanks to our guests, David Grinspoon, author of Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet, and Sally's twin sister, Eliza Helm. Grinspoon’s latest book is called Earth in Human Hands: Shaping Our Planet’s Future.