Lecturer: Prof. David J. Stevenson Affiliation: Caltech Abstract: Everything mixes with everything at sufficiently high temperature because of entropy. However, we are familiar with the concept of layered structures as in, for example, Earth's core and mantle and the expectation that Jupiter may have a core. I will talk about these two cases and their similarities and differences and argue that imperfect separation of core from mantle is a common feature of exoplanets larger than Earth and even may have implication for Earth itself, in particular the current problem with driving Earth's magnetic field for billions of years. Additional details of the upcoming Astrophysics' seminars can be found on the following link. ‏האירוע הזה כולל שיחת וידאו ב-Google Hangouts. הצטרף: https://hangouts.google.com/hangouts/_/mail.huji.ac.il/astrophysics?hceid=bWFpbC5odWppLmFjLmlsX2c0czhydDlpcmhwZzRvdGNybWIzZGFqcjdvQGdyb3VwLmNhbGVuZGFyLmdvb2dsZS5jb20.jsbqoaa2rgu1cae1gkpo0avjrs&hs=121