While we have become comfortably numb to the ideas of doomsayers like Nancy Lieder and prophets like Zechariah Sitchin, it should be noted that fear of the elusive Planet X, occasionally referred to as Nibiru, are not entirely crushed. The idea of a planet further out from Uranus and Neptune was first suggested by the famous Percival Lowell in 1894 when he observed irregularities in the orbits of those worlds.
A layman’s understanding of planetary mechanics is sufficient to alleviate fears of an entire planet shattering the Earth anytime soon, but this is not to say it has not happened in the past. A recent theory has proposed that our Moon is the result of a cataclysmic impact with a proto-planet named Theia. Some similarly suggest that such cataclysms are not out of the question for the future.
As well, a sufficiently large source of gravity does seem to be disturbing comets and asteroids in the far-flung Oort Cloud and Kuiper Belt. Some scientists find the number of short-period comets known today to be odd, still others find that our knowledge of such things is too new to tell.
Just because a naturally occurring Death Star is not presenting itself does not mean that large bodies in distant regions of our celestial neighborhood are not tossing rocks at our windshields. Mind the signs on the side of the road… especially the ones that read, “Falling Rocks Ahead.”
 (The Theia Hypothesis: New Evidence Emerges that Earth and Moon Were Once the Same, The Daily Galaxy, 5 July 2007. http://www.dailygalaxy.com/my_weblog/2007/07/the-theia-hypot.html, retrieved 29 May 2015.)
 (Bryner, Jeanna. Long Shot: Planet Could Hit Earth in Distant Future, Space.com, 10 June 2009. http://www.space.com/6824-long-shot-planet-hit-earth-distant-future.html, retrieved 29 May 2015.)
 (Bailey, M.E.; “The Near-Parabolic Flux and the Origin of Short-Period Comets,” Nature, 324:350, 1986.)
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