| Another difficulty that must be resolved is the current uncertainty about the consistency of cometary nuclei. |
| Indeed, the outermost asteroids show similarities with the cometary nuclei observed far from the Sun. |
| On the third, however, the cometary fragment was found, and its motion accurately measured. |
| These presumably cometary bodies, which reach several hundred kilometers in size, are vulnerable to severe perturbations by these planets. |
| The identification of volatile compounds present in the ices of cometary cores is not easy. |
| Relegated to the borders of the Solar system in a very cold environment, the cometary cores evolved very little since their formation. |
