Formation of flattened planetesimals by gravitational collapse of rotating pebble clouds

Vol. 681
10. Planets and planetary systems

Formation of flattened planetesimals by gravitational collapse of rotating pebble clouds

In their study, Lorek & Johansen delve into the fascinating process of how a kilometer-sized planetesimal might form from a rotating cloud of pebbles. They used a Monte Carlo method to simulate this complex process and find that when pebble clouds that rotate slowly collapse under their own gravity, they can form shapes such as flattened ellipsoids. This finding provides insights into the unique shapes of celestial bodies, such as the lobes of the contact binary Arrokoth and the bilobed comet 67P/Churyumov-Gerasimenko. The authors further explore how the initial spin of these pebble clouds influences the final shape of the planetesimal. With less angular momentum, the resulting planetesimal is almost spherical. But as the spin increases, the shape becomes more flattened and disk-like. This research suggests that the varied shapes of minor bodies in our Solar System – particularly those in the cold classical Kuiper belt and comets – can reveal a lot about the early shapes of planetesimals formed from these pebble clouds, providing a glimpse into the early stages of our Solar System's formation.