Pluto has a massive moon, Charon, which orbits it at a distance 16 times the radius of the dwarf planet. To explain this configuration, illustrated opposite in a montage of images taken in 2015 by the New Horizons probe, astronomers used the hydrodynamic model which made it possible, in 2001, to describe the collision between the Moon and the Earth, the assimilating to fluids without cohesive force. An American team led by Robert Melikyan (University of Arizona, in Tucson) proposes in Nature Geoscience from January 6 new simulations taking into account the solidity of the two bodies.
They put forward a scenario called “Kiss and Capture” where the two stars would have been, originally, made up of 85% rock and 15% ice. Proto-Charon would have had a mass twice that of today, and would have collided with Pluto at an angle of 45 degrees, at about 1 kilometer per second. A few dozen hours would have been enough for the future moon, having lost part of its mass, to rotate around the dwarf planet, before moving away towards its current circular orbit. In this scenario, Charon has remained relatively intact, retaining its core and most of its mantle, and would be as old as Pluto, whose radius (1,200 kilometers) is twice as large. The impact would have produced debris that could have contributed to the formation of Pluto's four other moons.
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