538: Asteroids: Rubble piles of the Solar System Astronomy Cast 538: Asteroids: Rubble piles of the Solar System by Fraser Cain & Dr. Pamela Gay Thanks to all the work from Hayabusa 2 and OSIRIS-REx, astronomers are getting a much better look at the smaller asteroids in the Solar System. It turns out, they're piles of  rubble... but fascinating piles of rubble. Let's talk about what we've learned so far.