The richest person in the world is obsessed with creating a city on Mars.

Elon Musk would like to see a million people living in a self-sufficient Martian settlement by 2050, both as a plan B for Earth and because it gives us something cool to get excited about.

Traveling to Mars has been a recurring theme of spacefaring fantasies for decades, from the German rocket innovator Wernher von Braun to science fiction writers Ray Bradbury and Kim Stanley Robinson. Human exploits on Mars have also been the subject of countless movies, TV shows, and comic books.

There are many good reasons to explore Mars. The discovery of water deep below the surface and ice at its poles suggests that the conditions to sustain life may have existed on the Red Planet, and perhaps still do. Studying Mars could teach us about how life emerged on Earth. While rovers have made great strides in uncovering the planet’s secrets, human explorers could accelerate the pace of discovery.

Living on Mars would bring many challenges for humans, among them cosmic and solar radiation exposure, an asphyxiating atmosphere, lower-than-Earth gravity, extreme temperatures, toxic soil, and no ready supply of food, drinkable water, or breathable air.

But our cultural and scientific fascination with Mars lives on. And if Musk’s SpaceX or a competitor lands humans on Mars in the coming years, it will be the realization of an ancient dream. To think that it all started with an optical illusion that tricked some astronomers into believing that Mars was riven with canals flanked with vegetation and carved by wise, peace-loving extraterrestrials.

Today, Explained co-host Sean Ramewaram spoke with David Baron, author of The Martians: The True Story of An Alien Craze that Captured Turn-of-the-Century America, about the belief in intelligent Martian life and the fixation........

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