Pluto (right) and its moon Charon, photographed by NASAs New Horizons probe in 2015NASA/JHUAPL/SwRIPluto and its moon Charon may have been briefly locked together in a cosmic kiss, before the dwarf planet released the smaller body and recaptured it in its orbit.Charon is the largest of Plutos five moons, with a radius more than half that of Pluto itself,but the question of how it came to orbit Pluto has puzzled astronomers. AdvertisementOne prominent theory suggests that Charon formed after a vast object smashed into Pluto, spewing debris into space that later formed Charon, similar to how scientists think Earths moon formed. But Charons large size and close orbit, at eight times wider than Pluto itself, make this a challenging scenario to explain.Now, Adeene Denton at the University of Arizona and her colleagues have proposed that Charon may have a less destructive origin story, which they describe as a kiss and capture.Previous simulations have treated Pluto and Charon as fluids an assumption that works when modelling collisions between larger bodies. But recent research has shown that with objects of lighter mass than Earths moon, the material strength of their composition influences the outcome. Pluto and Charon are quite small, so the assumption that they are fluid bodies probably no longer applies, says Denton. Voyage across the galaxy and beyond with our space newsletter every month.Sign up to newsletterThe researchers ran simulations that take into account Pluto and Charons compositions of rock and ice, and found that a more likely scenario involved a gentle sticking together and parting ways.Their model showed that a proto-Charon may have penetrated a proto-Plutos icy shell and the two bodies would have spun together rapidly for around 10 hours. Eventually, the spinning flung Charon back out and it settled into Plutos orbit.I had always assumed that any collision between planetary bodies that were hundreds of kilometres across would destroy the smaller one, if captured, says David Rothery at the Open University, UK.While the kiss-and-capture scenario is interesting, says Rothery, it will need to also explain the complex geological features seen on both Pluto and Charon, such as heavily cratered surfaces and icy volcanism, which it doesnt currently.Journal reference:Nature Geoscience DOI: 10.1038/s41561-024-01612-0Topics:Pluto