an comets is a mean of mankind
short_period_comet is periodic_comet. periodic_comet is comet. comets has solid_nucleus comet is astronomical_object. comets has ice long_period_comet is not periodic_comet. short_period_comet is not periodic_comet. comets is like_dirty_snowballs. periodic_comet is not comet. long_period_comet is periodic_comet.