Astronomers say they have evidence of a ninth planet in our solar system. Here's what they say they know about it. (Joel Achenbach,Gillian Brockell/The Washington Post)

If all goes according to wild conjecture, planet Earth and the planet Nibiru are set to collide in the autumn, twin cosmic shooters in a game of apocalyptic marbles. Nibiru is playing for keeps, bringing sinkholes, fire storms and the general annihilation of life as we know it. As with many conspiracy theories, though, this one has a fatal factual flaw. The closest thing Nibiru has had to an existence was a cameo in a 2013 Star Trek film. There is not, in reality, a planet called Nibiru boldly zooming through our solar frontier.

The fictitious shadow planet, according to Nibiru believers, is flung from the outskirts of the solar system dangerously close to Earth every 3,600 years. And, like its mysterious elliptical orbit, the heavenly body has a way of circling back in vogue. The most recent incarnation of Nibiru, as British tabloids and AOL News noted at the beginning of January, pencils in the apocalypse for October 2017.

The Plymouth Herald pointed to David Meade, author of the book “Planet X — The 2017 Arrival,” as the source of the current stir. Devastation, Meade crowed, will come in the form of Nibiru and several other tough-to-detect planets, which circle a brown dwarf called Nemesis. The planets, traversing large oval paths, remain hidden in far-off space — until they close in on Earth. And as roomy as those $25,000-a-pop doomsday bunkers in South Dakota may be, concrete and steel walls would offer little solace in the face of total planetary vaporization.

If the name Nibiru rings a bell, perhaps it flickered across your path as one of the many possible eschatons of 2012, tied to bogus Mayan end-of-the-world prophecies. As a concept, though, Nibiru predates both the 2012 hubbub and Meade’s doomsday scenario. Zecharia Sitchin, a former journalist and shipping industry executive, proposed the idea of Nibiru in his 1976 book “The Twelfth Planet: Book I of the Earth Chronicles.” (The other six chronicles include titles like “The Stairway to Heaven” and “The End of Days,” in which Sitchin wondered if the biblical cities of Sodom and Gomorrah were destroyed via nuclear bomb.)

Sitchin fancied himself an expert in the ancient Sumerian language. He determined that pre-cuneiform Sumerian documents included references to a planet called Nibiru. (Never mind that the term Nibiru was an object in Babylonian, not Sumerian, astronomy.)

From his translations sprang a plot out of a second-rate L. Ron Hubbard novel: On Nibiru lived aliens similar in stature to humans, except half again as tall. About half a million years ago, the rangy population of Nibiru decided to mine gold in Africa, landing a group of ancient astronauts on Earth. Here, the Nibiru astronauts genetically altered the native Earthlings — that is, the ancestors of you and me — into an exploitable working class.

“This is in the texts; I’m not making it up,” Sitchin told the New York Times in 2010, a few months before his death at age 90. “They wanted to create primitive workers from the Homo erectus and give him the genes to allow him to think and use tools.” Sitchin was opposed to the idea that Nibiru would come close to Earth in 2012. That would happen 1,000 years later, he said.

The concept mutated toward doomsday in 1995, when a self-avowed alien contactee and psychic Nancy Lieder warned about a collision with Nibiru on her site ZetaTalk. As outlandish as the prospect might seem, the concept took hold. In the estimation of NASA astrophysicist David Morrison, there are some 2 million websites devoted to what happens when Nibiru meets Earth.

If Nibiru had an anti-prophet, Morrison might very well fit the bill. Morrison has become something of an expert Nibiru debunker; it was a skill built up out of exposure. Morrison said in a July 2011 interview he was fielding five email queries to NASA about Nibiru daily.

Morrison elaborated on the subject in a 2011 video: There are no pictures or astronomical observations of Nibiru — but a planet nine months away from crashing into the Earth, cruising within the inner solar system, would be visible to the naked eye. (At a 2009 conference in California, Morrison pointed out, “No one could hide Nibiru if it existed.”) What’s more, an elliptical orbit that passed by every 3,600 years would alter the paths of Mars and Earth.

That Earth has a moon is a damning mark against Nibiru, too. The gravitational pull of a rogue planet “probably would have stripped the moon away completely,” the astrophysicist said. As for a hidden brown dwarf star like Nemesis, its effects would be even more dramatic.

More plausible, but not at all a harbinger of end times, is a possible Planet X. (The name Planet X denotes a suspected planet; before astronomer Clyde W. Tombaugh confirmed the existence of Pluto in 1930, the dwarf planet was referred to as Planet X.) In January 2016, researchers at the California Institute of Technology published a paper in Astronomical Journal, hypothesizing the existence of a “massive perturber” that altered the orbits of rocky bodies and dwarf planets on the fringes of our solar system.

Were a Planet Nine to exist — and its existence remains, at this point, speculation — the closest it would come to the sun would be 200 astronomical units; 1 astronomical unit is equal to the distance from the center of the earth to the center of the sun. Neptune, the farthest planet from the sun, sits at a distant and not-at-all apocalyptic 30 AU.

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