Mars

Mars is the fourth planet from the sun and the second smallest planet in the solar system. It's known as the Red Planet due to its ruddy red appearance in the sky. Mars is the most Earth like of all the other planets in the solar system.

 What is an Orbit?

An orbit is a regular, repeating path that one object in space takes around another one. An object in an orbit is called a satellite. A satellite can be natural, like the Earth or the Moon. It can also be man-made, like the Space Shuttle or the ISS.

Beyond the Blue Skies

Our Solar System is the Sun and the planetary system around it. A “planetary system” is a group of non-stellar object (planets, dwarf planets, moons, asteroids, meteoroids, comets and cosmic dust) which orbit around a star.

Dark Matter

Scientists think it makes up the bulk of matter in the universe, but it can neither be seen nor detected directly using current technologies. Candidates range from light-weight neutrinos to invisible black holes. Some scientists question whether dark matter is even real, and suggest that the mysteries it was conjured to solve could be explained by a better understanding of gravity.
http://www.space.com/9699-top-10-strangest-space.html