Lieder described Planet X as roughly four times the size of the Earth, and said that its perigee would occur, resulting in the Earth’s rotation ceasing for exactly 5.9 terrestrial days. This would be followed by the Earth’s pole destabilizing in a pole shift (a physical pole shift, with the Earth’s pole physically moving, rather than a geomagnetic reversal) caused by magnetic attraction between the Earth’s core and the magnetism of the passing planet. This in turn would disrupt the Earth’s magnetic core and lead to subsequent displacement of the Earth’s crust.

- From Wikipedia

Of course, like all big discoveries in the history of mankind, Lieder was condemned for her work and discredited by government officials not wanting to create mass panic. In recent years however, scientists have been discovering abnormalities in our solar system that agree with Lieder’s theories. Take a look at this article from 2008: Japanese scientists eye mysterious ‘Planet X’

Scientists at a Japanese university said Thursday they believed another planet up to two-thirds the size of the Earth was orbiting in the far reaches of the solar system.

The researchers at Kobe University in western Japan said calculations using computer simulations led them to conclude it was only a matter of time before the mysterious “Planet X” was found.

“Because of the very cold temperature, its surface would be covered with ice, icy ammonia and methane,” Kobe University professor Tadashi Mukai, the lead researcher, told AFP.

The study by Mukai and researcher Patryk Lykawka will be published in the April issue of the US-based Astronomical Journal.

“The possibility is high that a yet unknown, planet-class celestial body, measuring 30 percent to 70 percent of the Earth’s mass, exists in the outer edges of the solar system,” said a summary of the research released by Kobe University.

“If research is conducted on a wide scale, the planet is likely to be discovered in less than 10 years,” it said.

Planet X — so called by scientists as it is yet unfound — would have an oblong elliptical solar orbit and circle the sun every thousand years, the team said, estimating its radius was 15 to 26 billion kilometres.

Well, look at that. First it was a conspiracy theory, and now it’s being published in an Astronomical Journal. I’m not a conspiracy nut, but I don’t like it when people are called crazy only to be later proven right by their opposition. Keep an open mind people, and remember that history is written by those in power with only their own interests in mind.