If Charon hit Pluto at a relatively sedate speed of about 2,000 miles per hour — 10 times as slow as the Earth’s moon-forming impact — the two would have remained in contact for about 10 hours before gradually separating but remaining together. The researchers described this encounter as a “kiss and capture.” William McKinnon, a planetary scientist at Washington University in St. Louis, said that such a scenario “makes sense” given the large number of objects believed to be drifting around the Kuiper belt in the early solar system. “Collisional capture is probably a common process,” he said, with many other large binary objects also thought to exist in the Kuiper belt.