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

NASA artist’s conception of a brown dwarf (main) and stock image of the planets in the solar system (inset). An object between 2 and 50 times the mass of Jupiter may have flown through our ...

Saturn, Venus, Neptune, Uranus, Jupiter, Mars and Mercury will be visible in an uncommon planetary alignment this month.

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.

"With an orbital period of 570 days, it is a relatively cold gas giant planet," said Guðmundur Stefánsson of the University of Amsterdam in a statement. This orbital period places it a little closer ...

Pluto may not be a planet any more, but you still have a chance to see the distant dwarf planet at one of Michigan's ...

And red dwarf ... star where a planet with an atmosphere could retain liquid water on its surface. Wolk modeled atmospheric conditions similar to those of planets in our solar system, including ...

White dwarf stars could host habitable planets. Fast planetary rotation reduces cloud cover, keeping surface temperatures stable.

The dwarf planet ... reached the inner Solar System only later. For the current study, the researchers looked for previously unknown deposits of organic material on dwarf planet Ceres.

The seven planets will not be perfectly aligned, but will appear in an arc across the sky due to their orbital plane in the Solar System.