http://www.space.com/scienceastronom...ts_991014.html
In the October 11 issue of the Monthly Notices of the Royal Astronomical Society,
Dr. John Murray, an astronomer from the Open University in the United Kingdom proposed that a large object in the extreme outer realms of the solar system may be gravitationally affecting the orbits of long-period comets. He theorizes that the object would have to orbit the sun 32,000 times farther away than Earth (about 3 trillion miles) and would have to be at least as massive as Jupiter, if not more so. Given its distance, it would also be extremely faint and slow moving.
In other research, a professor of physics at the University of Louisiana at Lafayette, Dr. John J. Matese, is making a case for the existence of a 2- to 3-Jupiter mass object orbiting some 2.3 trillion miles from the sun. In a paper soon to be published in the planetary journal, Icarus, Dr. Matese asserts that this object, too,
***has created a "concentration" of Oort cloud comets and is responsible for sending a significant number of them - perhaps as much as 25 percent - into the inner solar system.