  Haumea, a rapidly rotating elongated dwarf planet (~ 1500 km in diameter),
has two satellites and is associated with a "family" of several smaller Kuiper
Belt objects (KBOs) in similar orbits. All members of the Haumea system share a
water ice spectral feature that is distinct from all other KBOs. The relative
velocities between the Haumea family members are too small to have formed by
catastrophic disruption of a large precursor body, which is the process that
formed families around much smaller asteroids in the Main Belt. Here we show
that all of the unusual characteristics of the Haumea system are explained by a
novel type of giant collision: a graze-and-merge impact between two comparably
sized bodies. The grazing encounter imparted the high angular momentum that
spun off fragments from the icy crust of the elongated merged body. The
fragments became satellites and family members. Giant collision outcomes are
extremely sensitive to the impact parameters. Compared to the Main Belt, the
largest bodies in the Kuiper Belt are more massive and experience slower
velocity collisions; hence, outcomes of giant collisions are dramatically
different between the inner and outer solar system. The dwarf planets in the
Kuiper Belt record an unexpectedly large number of giant collisions, requiring
a special dynamical event at the end of solar system formation.
