Answer: comet
Step-by-step explanation:
A comet is a body found in the outskirts of the solar system in Kuiper belt or Oort clouds beyond the orbit of Neptune. A comet has core which rocky formed from the debris of the solar system. The core is known as nucleus which is surrounded by atmosphere of frozen gases. Comets orbit the Sun in elliptical path and enter the system when their path is perturbed by the disturbance in nearby star.