[meteorite-list] Giant Kuiper Belt Planetoid Sedna May Have Formed Far Beyond Pluto

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jan 11 14:16:09 2005
Message-ID: <200501111915.LAA10034_at_zagami.jpl.nasa.gov>

http://www.swri.org/9what/releases/2005/Sedna.htm

Giant Kuiper Belt planetoid Sedna may have formed far beyond Pluto
Southwest Research Institute (SwRI) News
January 10, 2005

Boulder, Colo. -- 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."

The new Sedna formation study used a planetary accretion code developed
by Stern with funding from NASA's Origins of Solar System's Program in
the late 1990s for studies of the formation of Kuiper Belt Objects. This
software was used to explore the feasibility of building Sedna from
boulder-sized and other small bodies at distances between 75 AU (Sedna's
closest solar approach distance) and 500 AU (Sedna's average distance
from the Sun). Stern's Sedna formation simulations assumed that Sedna's
original orbit, while distant from the Sun, was circular. Astronomers
agree that Sedna could not have formed in its present, eccentric orbit
because such an orbit allows only violent collisions that prevent the
growth of small bodies. Stern's simulations further assumed that the
solar nebula -- the disk of material out of which the planets formed --
was much more extended than most previous simulations had assumed.

"The Sedna formation simulations assumed that the primordial solar
nebula was a disk about the size of those observed around many nearby
middle-aged stars -- like the well-known example of the 1,500-AU-wide
disk around the star Beta Pictoris," Stern says.

"The model calculations found that objects as large, or even larger,
than Sedna could easily form in circular orbits at distances of 75 to
500 AU, and that their formation time could have been fairly short --
just a few percent the age of the solar system," Stern continues. "If
Sedna did form this far out, it is likely to be accompanied by a cohort
of other large planetoids in this very distant region of the solar
system. One telltale sign that these objects were formed where they are,
rather than in another location, would be if a good fraction of them are
on near circular orbits."

Editors: An image to accompany this story is available at
http://www.swri.org/press/sedna.htm .

For more information contact Maria Martinez (mmartinez_at_swri.org)
Communications Department, at (210) 522-3305, PO Drawer 28510, San
Antonio, TX 78228-0510, or Dr. Alan Stern
(alan_at_boulder.swri.edu) at (303) 546-0262.

 
Received on Tue 11 Jan 2005 02:15:57 PM PST