As NASA's New Horizons spacecraft zooms nearer to Pluto and its five known moons, scientists are expecting not only greatly enhanced views of the Plutonian system, but to discover more moons and perhaps unknown rings.
These discoveries could help explain what created the tiny system -- or they could destroy New Horizons before it has a chance to relay its precious data.
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"The New Horizons mission provides an opportunity to reveal the compositions of the moons," said Richard Binzel, a member of the mission's science team and a planetary scientist at the Massachusetts Institute of Technology. "The compositions are the next step to decoding their origins."
Telescope studies have found that the moons vary a great deal in brightness. That suggests they are made of different mixes of materials, and so they have different origins and were possibly captured by Pluto at different times. On the other hand, their neatly arranged orbits around Pluto strongly suggest the opposite: that they formed at the same time, perhaps from an ancient collision that left Pluto orbited by Charon, the other moons and perhaps rings of debris.
The currently most accepted theory is the collision, which gives the Pluto-Charon, et al., system a lot in common with the Earth-Moon system, that is thought to have formed in the same manner when a Mars-sized body slammed into the early Earth and created our unusually large natural satellite.
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"Charon is half as big as Pluto," said Mark Showalter, a planetary scientist at the SETI Institute who is involved in efforts to search for hazardous debris along New Horizons' flight path at Johns Hopkins University Applied Physics Laboratory. "So that's the consensus: Charon is debris from this collision."
But the collision picture is far from complete.
"The question is the little guys," said Showalter, meaning the smallest moons Styx, Nix, Hydra and Kerberos. The collision theory sounds really good, he said, except that no one has been able to reproduce the system accurately in a model. So all bets are off until there is more data -- which New Horizons could very well provide.