• celestial mechanics;
  • kuiper belt: general;
  • minor planets, asteroids: general;
  • minor planets, asteroids: individual: (15810) 1994 JR1;
  • planets and satellites: individual: Pluto


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. Although they share the semi-major axis and the mean longitude of their host body, their eccentricity and inclination may be very different. So far, minor bodies temporarily trapped in the quasi-satellite dynamical state have been identified around Venus, the Earth, the dwarf planet (1) Ceres, the large asteroid (4) Vesta, Jupiter and Saturn. Using computer simulations, Tiscareno & 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 years. 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 (15810) 1994 JR1 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 the plutino (15810) 1994 JR1 the first minor body moving in a 1:1 mean motion resonance with Pluto and the first quasi-satellite found in the trans-Neptunian region. 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, the plutino (15810) 1994 JR1 could be considered as a possible secondary target for NASA’s Pluto–Kuiper Belt Mission New Horizons after the main Pluto flyby in 2015. This opens the possibility of studying at first hand and for the first time a minor body in the quasi-satellite dynamical state.