Planet X to crash into Earth?

Planet X revived

See also: The "Kuiper cliff" and hypothetical planetary object

The search for Planet X may not be over yet. The Kuiper Belt terminates suddenly at a distance of 55 AU from the Sun, and there is some speculation this sudden dropoff may be caused by the presence of an object with a mass between that of Mars and Earth located beyond 55 AU. Noted proponents of this hypothesis include Alan Stern, head of NASA's New Horizons mission to Pluto,[10] and Patryk Lykawka, astronomer at Kobe University, Japan, who claims that we will discern this object's existence or lack thereof by 2013.[11] Lykawka's computer simulations suggest that a body roughly the size of Earth, ejected outward by Neptune early in the Solar System's formation and currently set in elongated orbit between 80 and 170 AU from the Sun, could explain not only the Kuiper cliff but also the peculiar "detached" TNOs such as 90377 Sedna. While some astronomers have cautiously supported Lykawka's claims, others have dismissed them as contrived.[11]

An alternative theory, proposed in 1999 by John Murray of the Open University and John Matese, Patrick Whitman and Daniel Whitmire of the University of Louisiana at Lafayette, has long period comets originating from specific regions of the sky, rather than coming from random directions as proposed by Oort. This would result from comets being disturbed by an unseen object at least as large as Jupiter, and possibly a brown dwarf.[12]