The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

All must, then, be regarded as having always been members of the solar system, however much their orbits may have changed. They are supposed to be derived from the secondary nuclei of a soiral nebula.

An object eight times the mass of Jupiter may have swooped around the sun, coming superclose to Mars' present-day orbit ...

A new study implies that in the past, moons in our solar system may have had rings just like planets do — deepening the mystery of why no ringed moons exist today.

The organic ingredients to life, hints to where Earth’s water came from, and the fundamental building blocks of our planet ...