When most people think of our Solar System, they think of the 8 planets officially recognized by the International Astronomical Union (IAU). But what if I told you there are at least 40 planets, and ...

But this definition of the solar system is considered to be far too simple by some astronomers, such as Caltech's Mike Brown. "It's not really true," Brown told Live Science in an email.

Rocky bodies called protoplanets were thought to have formed slightly earlier in the inner solar system than those beyond the ...

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 ...

The proposed new definition contains quantifiable criteria that can be applied for defining planets inside and outside our solar system. In the new definition, a planet is a celestial body that: ...

Though Pluto has formally been considered a dwarf planet for almost two decades, it still has many lessons left for planetary scientists — including hints about how the solar system formed.

Planetary scientists are proposing a new definition of a planet to replace one that many researchers view as sun-centric and outdated. The current definition — established in 2006 by the International ...