Lastrophysicists around the world are scanning space for Planet X, that extra giant planet in the solar system determined by calculating its gravitational effects. This is the 12th planet, announced in 1976 by Zecharia Sitchin. In this book, Sitchin develops his theory that an ancient alien civilization visited Earth thousands of years ago. According to him, these extraterrestrials, whom he calls the “Annunaki”, would come from an unknown planet located in our solar system, which he identifies as the “twelfth planet”. This planet would have an unusual, elliptical orbit that would cause it to come closer to Earth every few thousand years.