Neptune's capture of its moon Triton in a binary–planet gravitational encounter

摘要: Unique among the Solar System's large satellites, Triton orbits Neptune in direction opposite to planet's spin. Triton's circular orbit is also tilted significantly from Neptune's equator. These facts suggest that satellite once orbited Sun before capture by Neptune, but previous models of required improbable events. Craig Agnor and Douglas Hamilton have developed a more natural explanation. In this model, was member binary may been rather like Pluto its largest moon Charon. The pair strayed too close were torn apart; companion escaped, left behind. cover depicts encounter. primordial satellites would not survived long after capture. (Graphic based on planetary maps provided Steve Albers, Jerry Gardner, James Hastings-Trew, Constantine Thomas NOAA's ‘Science Sphere’ project.) principal far retrograde System (its mass ∼40 per cent greater than Pluto). Its inclined lies between group small inner prograde number exterior irregular with both orbits. This unusual configuration has led belief originally being captured around Neptune1,2,3. Existing models4,5,6 for capture, however, all significant bottlenecks make their effectiveness doubtful. Here we report three-body gravitational encounter system (of ∼103-kilometre-sized bodies) likely explanation Our model predicts range plausible characteristics, including ones similar Pluto–Charon pair.