[meteorite-list] Pluto-Charon Origin May Mirror that of Earth and Its Moon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Jan 28 16:17:45 2005
Message-ID: <200501282117.NAA24125_at_zagami.jpl.nasa.gov>

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

SwRI scientist: Pluto-Charon origin may mirror that of Earth and its Moon
Southwest Research Institute (SwRI) News Release
January 27, 2005

Boulder, Colo. - The evolution of Kuiper Belt
objects, Pluto and its lone moon Charon may have something in common
with Earth and our single Moon: a giant impact in the distant past.

Dr. Robin Canup, assistant director of Southwest Research Institute's?
(SwRI) Department of Space Studies, argues for such an origin for the
Pluto-Charon pair in an article for the January 28 issue of the journal
Science.

Canup, who currently is a visiting professor at the California Institute
of Technology, has worked extensively on a similar "giant collision"
scenario to explain the Moon's origin.

In both the Earth-Moon and Pluto-Charon cases, Canup's smooth particle
hydrodynamic simulations depict an origin in which a large, oblique
collision with the growing planet produced its satellite and provided
the current planet-moon system with its angular momentum.

While the Moon has only about 1 percent of the mass of Earth, Charon
accounts for a much larger 10 to 15 percent of Pluto's total mass.
Canup's simulations suggest that a proportionally much larger impactor -
one nearly as large as Pluto itself - was responsible for Charon, and
that the satellite likely formed intact as a direct result of the collision.

According to Canup, a collision in the early Kuiper Belt - a disk of
comet-like objects orbiting in the outer solar system beyond Neptune -
could have given rise to a planet and satellite with relative sizes and
angular rotation characteristics consistent with those of the
Pluto-Charon pair. The colliding objects would have been about 1,600 to
2,000 kilometers in diameter, or each about half the size of the Earth's
Moon.

"This work suggests that despite their many differences, our Earth and
the tiny, distant Pluto may share a key element in their formation
histories. This provides further support for the emerging view that
stochastic impact events may have played an important role in shaping
final planetary properties in the early solar system," said Canup.

The "giant impact" theory was first proposed in the mid-1970s to explain
how the Moon formed, and a similar mode of origin was suggested for
Pluto and Charon in the early 1980s. Canup's simulations are the first
to successfully model such an event for the Pluto-Charon pair.

Simulations published by Canup and a colleague in Nature in 2001 showed
that a single impact by a Mars-sized object in the late stages of
Earth's formation could account for the iron-depleted Moon and the
masses and angular momentum of the Earth-Moon system.

This was the first model to simultaneously explain these characteristics
without requiring that the Earth-Moon system be substantially modified
after the lunar forming impact.

This research was supported by the National Science Foundation under
grant no. AST0307933.

Editors: An animation of a simulation of a potential Pluto-Charon
forming collision can be downloaded from
http://www.swri.org/press/2005/plutocharon.htm.

For more information, contact Joe Fohn
(jfohn_at_swri.org;com67@swri.org)
Communications Department, at (210) 522-4630, Southwest
Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510.
Received on Fri 28 Jan 2005 04:17:32 PM PST