The location of the solar system's outer boundary is a point of contention among astronomers. There are three possible candidates, which "all have merit." But which one is best?

An illustration of the solar system (not to scale), including the sun, inner rocky planets, asteroid belt, the outer gassy planets, and—beyond Neptune—the Kuiper belt and the Oort cloud.

NASA has revealed that they have sent a man-made machine further than they ever have before, and they said they made an odd ...

Astronomers are proposing a new, more quantitative definition of what makes a planet. The new definition looks more directly ...

Many smaller outer solar system objects appear to have orbits that are aligned in certain mysterious ways; the simplest explanation is that their motions are influenced by another, as-yet-unseen ...

A hidden structure at the farthest reaches of our solar system is challenging long-held theories. Using advanced simulations, a NASA supercomputer has revealed that the Oort Cloud, a vast shell of ...