sentences: a comet orbit occurs usually once per 1000 years
docs: interstellar_comet is exosolar_comet. comets has set_orbits short_period_comet is periodic_comet. comet is subplanetary_stellar_orbiter. bound_orbit is orbit. long_period_comet is periodic_comet. periodic_comet is comet. comet is icy_planetary_body. interstellar_comet is exocomet.