The Oort Cloud

The Oort cloud is a huge region of icy objects surrounding our Sun. We’re not sure it exists, but we think it’s where comets come from.

I’ve often seen the Oort cloud drawn as a vague round blob. But recently some people simulated it—and discovered that tidal forces from the Milky Way may pull it into a much more interesting shape:

• David Nesvorný, Luke Dones, David Vokrouhlický, Hal F. Levison, Cristian Beaugé, Jacqueline Faherty, Carter Emmart, and Jon P. Parker, A spiral structure i...