[meteorite-list] SwRI Study Finds That Pluto Satellites' Orbit Ballet May Hint of Long-Ago Collisions

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 10 Oct 2013 14:01:06 -0700 (PDT)
Message-ID: <201310102101.r9AL16Ap014981_at_zagami.jpl.nasa.gov>

http://www.swri.org/9what/releases/2013/pluto-moon.htm

SwRI study finds that Pluto satellites' orbital ballet may hint of long-ago collisions
Southwest Research Institute
Embargoed for release at 1 p.m. CDT on Wednesday, Oct. 9, 2013

Boulder, Colo. - Oct. 9, 2013 - A large impact 4 billion years ago may
account for the puzzling orbital configuration among Pluto's five known
satellites, according to a new model developed by planetary scientists
from Southwest Research Institute (SwRI).

Starting with Charon, Pluto's nearest and largest moon, each of the successively
more distant - and much smaller - moons orbits Pluto according to a steadily
increasing factor of Charon's own orbital period. The small satellites,
Styx, Nix, Kereberos and Hydra, have orbital periods that are almost exactly
3, 4, 5 and 6 times longer than Charon's.

"Their distance from Pluto and the orbital arrangement of the satellites
has been a challenge for theories of the small satellites' formation,"
said lead investigator Dr. Harold "Hal" Levison, an Institute scientist
in SwRI's Planetary Science Directorate at Boulder, Colo.

Models for the formation of Charon leave plenty of small satellites, but
all of them are much closer to Pluto than the current system that we see
today,' said Levison. A major problem has been understanding how to move
these satellites outward, but not lose them from the Pluto-Charon system
or have them crash into Charon. He said, 'This configuration suggests
that we have been missing some important mechanism to transport material
around in this system."

The SwRI study, funded by a grant from NASA's Outer Planetary Research
program and Lunar Science Institute, considered the earliest and most
dynamic epoch of the Pluto/Charon system. It is thought that Charon was
formed by a large impact during a period in solar system history when
such collisions were dramatically more frequent. Any initially surviving
satellites would likely be destroyed in collisions, but these shattered
moons wouldn't be lost; rather, their remains would stay in the Pluto/Charon
system and become the starting point for building new satellites. Thus
there would have been many generations of satellite systems over the history
of Pluto and Charon.

In modeling the destruction of the satellites, the SwRI study found that
there may be a method for moving them, or their building blocks, outward,
due to the competing effects of Charon's gravitational kicks and collisions
among the debris of the disrupted satellites. Charon is the largest satellite
of any planet or dwarf-planet, weighing in at 1/10 the mass of Pluto (the
Moon is just 1/81 the mass of Earth), and so it could rapidly slingshot
the small satellites outward if they were to approach too closely. Meanwhile,
collisions among small satellites can change orbits to keep things away
from Charon. When combined, this leads to a series of satellites colliding,
breaking to pieces, moving outward and then rebuilding.

"The implications for this result are that the current small satellites
are the last generation of many previous generations of satellites," said
Dr. Kevin Walsh, another investigator and a research scientist in SwRI's
Planetary Science Directorate at Boulder, Colo. "They were probably first
formed around 4 billion years ago, and after an eventful million years
of breaking and rebuilding, have survived in their current configuration
ever since."

This work used the Extreme Science and Engineering Discovery Environment
(XSEDE) digital collection, which is supported by National Science Foundation
grant number OCI-1053575.
Received on Thu 10 Oct 2013 05:01:06 PM PDT