  In the solar system, quasi-satellites move in a 1:1 mean motion resonance
going around their host body like a retrograde satellite but their mutual
separation is well beyond the Hill radius and the trajectory is not closed as
they orbit the Sun not the host body. So far, minor bodies temporarily trapped
in the quasi-satellite dynamical state have been identified around Venus,
Earth, the dwarf planet (1) Ceres, the large asteroid (4) Vesta, Jupiter,
Saturn and Neptune. Using computer simulations, Tiscareno and Malhotra have
predicted the existence of a small but significant population of minor bodies
moving in a 1:1 mean motion resonance with Pluto. Here we show using N-body
calculations that the Plutino 15810 (1994 JR1) is currently an accidental
quasi-satellite of Pluto and it will remain as such for nearly 350,000 yr. By
accidental we mean that the quasi-satellite phase is triggered (or terminated)
not by a direct gravitational influence in the form of a discrete close
encounter but as a result of a resonance. The relative mean longitude of the
Plutino circulates with a superimposed libration resulting from the oscillation
of the orbital period induced by the 2:3 mean motion resonance with Neptune.
These quasi-satellite episodes are recurrent with a periodicity of nearly 2
Myr. This makes 15810 the first minor body moving in a 1:1 mean motion
resonance with Pluto. It also makes Pluto the second dwarf planet, besides
Ceres, to host a quasi-satellite. Our finding confirms that the quasi-satellite
resonant phase is not restricted to small bodies orbiting major planets but is
possible for dwarf planets/asteroids too. Moreover, 15810 could be considered
as a possible secondary target for NASA's Pluto-Kuiper Belt Mission New
Horizons after the main Pluto flyby in 2015.
