  Asteroid (514107) 2015 BZ509 was discovered recently in Jupiter's co-orbital
region with a retrograde motion around the Sun. The known chaotic dynamics of
the outer Solar System have so far precluded the identification of its origin.
Here, we perform a high-resolution statistical search for stable orbits and
show that asteroid (514107) 2015 BZ509 has been in its current orbital state
since the formation of the Solar System. This result indicates that (514107)
2015 BZ509 was captured from the interstellar medium 4.5 billion years in the
past as planet formation models cannot produce such a primordial
large-inclination orbit with the planets on nearly-coplanar orbits interacting
with a coplanar debris disk that must produce the low-inclination small-body
reservoirs of the Solar System such as the asteroid and Kuiper belts. This
result also implies that more extrasolar asteroids are currently present in the
Solar System on nearly-polar orbits.

Earth and Planetary Astrophysics