Pluto (right) and its moon Charon, photographed by NASA’s New Horizons probe in 2015
NASA/JHUAPL/SwRI
Pluto and its moon Charon may have been locked together in a cosmic “kiss” before the dwarf planet released the smaller body and returned to its orbit.
Charon is the largest of Pluto’s five moons, with a radius more than half that of Pluto itself, but how it got into Pluto’s orbit has puzzled astronomers.
One outstanding theory suggests that Charon was created after a large object smashed into Pluto, then ejecting the debris that created Charon into space, similarly. how scientists think the Earth’s moon was formed. But Charon’s large size and close orbit, eight times wider than Pluto itself, make this scenario challenging to explain.
now, Adeene Denton At the University of Arizona and his colleagues have proposed that Karon may have a less destructive origin story, which they describe as “kiss and capture”.
Previous simulations have treated Pluto and Charon as fluids, an assumption that works when modeling collisions between larger bodies. But recent studies have shown that with objects with a lighter mass than Earth’s moon, the material strength of their composition affects the result. “Pluto and Charon are quite small, so the idea that they are probably fluid bodies doesn’t work,” says Denton.
The researchers ran simulations that took into account the rock and ice compositions of Pluto and Charon, and found that one likely scenario involved them gently clinging to each other and breaking apart.
Their model showed that a proto-Charon could have entered the icy shell of proto-Pluto and the two bodies rotated rapidly for about 10 hours. Eventually, the spin kicked Charon out and into Pluto’s orbit.
“I’ve always thought that collisions between planetary bodies hundreds of kilometers away would destroy the smallest, if caught,” he says. David Rothery at the Open University, UK.
While the kiss-and-capture scenario is interesting, Rothery says, it will also have to explain the complex geological features seen on both Pluto and Charon, such as cratered surfaces and icy volcanism, which are absent today.
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