Does our Solar System have 9 planets or only 8? Astronomers have gone back and forth on that a lot, with Pluto now being classified as a dwarf planet. However, out beyond Neptune there could be ...

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

Stargazers will be treated to a rare seven-planet alignment in February. This is what scientists hope to learn.

This may explain the strange properties of the orbits of our solar system's planets, which are not quite perfectly circular, and all lie on slightly different planes. NASA artist’s conception of ...

All seven of the other planets in our solar system are about to become visible at once in a great planetary alignment – here’s how to spot the celestial show ...

An object eight times the mass of Jupiter may have swooped around the sun, coming superclose to Mars' present-day orbit before shoving four of the solar system's planets onto a different course.

NASA said the system is thought to be moving at least 1.2 million miler per hour, nearly twice as fast as our solar system.