  Pluto's first known moon, Charon, was discovered in 1978 (Christy 1978) and
has a diameter about half that of Pluto (Buie 1992,Young 1994, Sicardy 2005),
which makes it larger relative to its primary than any other moon in the Solar
System. Previous searches for other satellites around Pluto have been
unsuccessful (Stern 1991, Stern 1994, Stern 2003), but they were not sensitive
to objects <=150 km in diameter and there are no fundamental reasons why Pluto
should not have more satellites (Stern 1994). Here we report the discovery of
two additional moons around Pluto, provisionally designated S/2005 P1
(hereafter P1) and S/2005 P2 (hereafter P2), which makes Pluto the first Kuiper
belt object (KBO) known to have multiple satellites. These new satellites are
much smaller than Charon (diameter~1200 km), with P1 ranging in diameter from
60-165 km depending on the surface reflectivity, and P2 about 20% smaller than
P1. Although definitive orbits cannot be derived, both new satellites appear to
be moving in circular orbits in the same orbital plane as Charon, with orbital
periods of ~38 days (P1) and ~25 days (P2). The implications of the discovery
of P1 and P2 for the origin and evolution of the Pluto system, and for the
satellite formation process in the Kuiper belt, are discussed in a companion
paper (Stern 2006).
