[meteorite-list] Pluto's New Moons Likely Born with Charon; Pluto May Even Have Rings

[Ron Baalke]

http://www.swri.org/9what/releases/2006/Pluto.htm

Communications Department
Southwest Research Institute
PO Drawer 28510
San Antonio, Texas

For more information contact:

Maria Martinez, (210) 522-3305
or
Dr. Alan Stern, (303) 324-5269

February 22, 2006

Pluto's New Moons Likely Born with Charon; Pluto May Even Have Rings

Boulder, Colorado -- In a paper published today in Nature, a team of U.S. 
scientists led by Dr. S. Alan Stern of Southwest Research Institute® 
(SwRI®), concludes that two newly discovered small moons of Pluto were 
very likely born in the same giant impact that gave birth to Pluto's much 
larger moon, Charon. The team also argues that other, large binary Kuiper 
Belt Objects (KBOs) may also frequently harbor small moons, and that the 
small moons orbiting Pluto may generate debris rings around Pluto.

The team making these findings included Drs. Bill Merline, John Spencer, 
Andrew Steffl, Eliot Young and Leslie Young of SwRI; Dr. Hal Weaver of the 
Johns Hopkins University Applied Physics Laboratory; Max Mutchler of the 
Space Telescope Science Institute; and Dr. Marc Buie of the Lowell 
Observatory. This team discovered Pluto's two small moons in 2005 using 
sensitive images obtained by the Hubble Space Telescope, as reported by 
Weaver et al. in an accompanying paper in the February 23 issue of Nature.

"The evidence for the small satellites being born in the Charon-forming 
collision is strong; it is based around the facts that the small moons are 
in circular orbits in the same orbital plane as Charon, and that they are 
also in, or very near, orbital resonance with Charon," says lead author 
Stern, executive director of the SwRI Space Science and Engineering 
Division.

"Tests of this scenario will come from refined orbital data, from 
measuring the rotational periods of these moons, and from determinations 
of their densities and surface compositions," says co-author Weaver.

Collisions, both large and small, are major processes that shaped many 
aspects of our solar system. Scientists use computer simulations to study 
the origin of planetary systems formed by impact events of a scale much 
larger than could be simulated in a laboratory. Another large collision, 
like the one thought to have created Charon and Pluto's small moons, is 
believed responsible for the formation of the Earth-moon pair.

"The idea that Pluto's small moons and Charon resulted from a giant impact 
now seems compelling. Future simulations to determine the characteristics 
of the impact required to produce all three satellites should provide 
improved constraints on the early dynamical history of the Kuiper Belt," 
adds Dr. Robin Canup, director of SwRI's Space Studies Department, who in 
2005 produced the most comprehensive models to date of the Charon-forming 
impact.

Based on the growing realization that binary "ice dwarf" pairs like 
Pluto-Charon are common in the Kuiper Belt, the Pluto satellite discovery 
team concludes that numerous triple, quadruple and even higher-order 
systems may be discovered across the Kuiper Belt in years to come.

"Finding small satellites around KBOs is difficult because their large 
distance from the Sun makes them appear very faint. As a result, we don't 
really know how common it is for KBOs to have multiple satellites," adds 
co-author Steffl. "One good way to test this is to search around objects 
that have been ejected from the Kuiper Belt into orbits that bring them 
much closer to the Sun. So far, about 160 of these objects, called 
Centaurs, have been discovered. We hope to use Hubble to search for faint 
moons around some of them."

Co-author Merline adds, "If Pluto's small moons generate debris rings from 
impacts on their surfaces, as we predict, it would open up a whole new 
class of study because it would constitute the first ring system seen 
around a solid body rather than a gas giant planet."

"The Pluto system never fails to reward us when we look at it in new 
ways," concludes Stern. "What a bonanza and an illustration of the 
richness of nature Pluto has consistently proved to be. Our discovery of 
its two new moons reinforces that lesson yet again."

The paper, "A Giant Impact Origin for Pluto's Small Moons and Satellite 
Multiplicity in the Kuiper Belt," by Stern et al. is available in the 
February 23 issue of Nature. NASA funded this work.

Editors: An image to accompany this story is available at
     http://www.swri.org/press/2006/plutoimpact.htm