  Dozens of families of asteroids in the asteroid belt have similar orbits and
compositions because they formed through a collision. However, the icy debris
beyond the orbit of Neptune, called the Kuiper Belt, contains only one known
family, the Haumea family. So far, no self-consistent explanation for the
formation of the Haumea family can match all geophysical and orbital
characteristics of the family without invoking extremely improbable events.
Here, we show that the family is adequately explained as the product of a
merging binary near the end of Neptune's orbital migration. The unique orbital
signature of a merging binary, which was not found in extensive searches, is
effectively erased during the final stages of migration, providing an
explanation for all aspects of the Haumea family. By placing the formation of
the Haumea family in the broader context of solar system formation, we
demonstrate a proof-of-concept model for the formation of Haumea.
