Recently, astronomers reported the surprising discovery of a very large diameter Kuiper Belt planetoid -- (90377) Sedna -- on a distant, 12,500-year-long, eccentric orbit centered approximately 500 astronomical units from the Sun. Sedna's estimated diameter is about 1,600 km, two-thirds that of Pluto. Initial studies of Sedna's origin have speculated that it might have been ejected from the giant planets region of our solar system far inside the orbit of Pluto, or perhaps was captured from a passing star's Kuiper Belt.
In a report published in the January 2005 issue of The Astronomical Journal, planetary scientist Dr. Alan Stern of the Space Science and Engineering Division at Southwest Research Institute® (SwRI®) shows Sedna could have formed far beyond the distance of Pluto.
"If this is actually what happened," Stern points out, "it would indicate that our solar system's planet factory operated across a much larger region than previously thought." It would also indicate that the mysterious Kuiper Belt "edge" near 50 AU (one AU is the distance from the Earth to the Sun) is not an outer edge, but simply the inner edge of an annular trough, or gap, that is carved out of a much broader structure that has been called the "Kuiper disk."