Why should the cores of Uranus and Neptune have formed so late? Probably because the icy planetesimals from which they formed were more widely dispersed at their greater distances from the Sun. With more space between planetesimals, it would take longer to build up these two planets’ cores. Saturn may have captured less gas than Jupiter both because its core formed somewhat later and because less gas was available at its greater distance from the Sun. As we will discuss in Section 10.7, some astronomers think that Uranus and Neptune might have formed in a location different from where they are now.