Two large asteroids in the main belt are spinning as fast as a fairground ride, a pace that should tear them apart if they are loose piles of rubble held together only by gravity. The discovery, reported by New Scientist, challenges a common assumption that the biggest asteroids are weak, gravitationally bound aggregates.
At the measured spin rates, the centrifugal force at the equator should exceed the gravitational pull holding the rock together. That means the asteroids must have some internal strength or cohesion beyond gravity, or the standard model of asteroid structure needs revision.
The finding is based on observations of two objects, so it is not yet clear how widespread such strong asteroids are. But if other large asteroids spin this fast, planetary scientists may need to rethink how these bodies form and evolve.