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Harvard's top astronomer lays out his controversial theory that our solar system was recently visited by advanced alien technology from a distant star.

"Provocative and thrilling ... Loeb asks us to think big and to expect the unexpected."--Alan Lightman, New York Times bestselling author of Einstein's Dreams and Searching for Stars on an Island in Maine

In late 2017, scientists at a Hawaiian observatory glimpsed an object soaring through our inner solar system, moving so quickly that it could only have come from another star. Avi Loeb, Harvard's top astronomer, showed it was not an asteroid; it was moving too fast along a strange orbit, and left no trail of gas or debris in its wake. There was only one conceivable explanation: the object was a piece of advanced technology created by a distant alien civilization.

In Extraterrestrial, Loeb takes readers inside the thrilling story of the first interstellar visitor to be spotted in our solar system. He outlines his controversial theory and its profound implications: for science, for religion, and for the future of our species and our planet. A mind-bending journey through the furthest reaches of science, space-time, and the human imagination, Extraterrestrial challenges readers to aim for the stars--and to think critically about what's out there, no matter how strange it seems.