List of planets
This is a list of two types of planets: standard planets and dwarf planets, in the Solar System.
Planets in the Solar System
- Terrestrial planets
- Mercury – The planet with the second highest temperature in the Solar System and the closest planet to the Sun.
- Venus – The warmest planet. Sometimes called "Earth's twin" because Venus and Earth are very similar.
- Earth – The only planet that is known to have life. It has one natural satellite, the Moon.
- Mars – Sometimes called the "red planet" and "the brother of Earth".
Other
- Pluto – the smallest planet, Pluto is now considered a "Dwarf planet" by the International Astronomical Union (IAU) since August 24, 2006.
- Theia – Hypothetical planet which some think crashed into Earth and created the Moon.
- Planet Nine – a hypothetical planet beyond Neptune. It has not been found, but some astronomers think its gravity pulls on the orbits of many dwarf planets. It is thought to be a gas giant.
Dwarf planets
- Ceres is the largest asteroid (not to mention plutinos) in the Solar System's main asteroid belt.
- Haumea is shaped like an egg.
- Makemake crosses paths with Eris.
- Eris follows the most elliptical path of any planet.
Exoplanets
Definition of a planet
Technically, there was never a scientific definition of the term planet before 2006. When the Greeks observed the sky thousands of years ago, they discovered objects that acted differently than stars. These points of light seemed to wander around the sky throughout the year. The term "planet" derives from the Greek word "planets" - wanderer.
In 2006, the International Astronomical Union (IAU) convened a Planet Definition Committee, deliberated, and ultimately reached a consensus on a new definition of a planet which leaves us with the eight planets we today consider to comprise the Solar System (thus the exit of Pluto). That new definition: " A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit [meaning: 'there are no other bodies in its path that it must sweep up as it goes around the Sun'.]"