List of planets
Planets in the Solar System[change | change source]
- 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
- 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".
- Pluto – (disputed) Historically considered the smallest planet, Pluto is now considered a "Dwarf Planet" by the International Astronomical Union (IAU) when they developed a definition for "planet" on August 24, 2006. Other organizations disagreed.
- Gas giants
Dwarf planets[change | change source]
- Ceres is the largest asteroid (not mentioning 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.
Other[change | change source]
Some scientists think that there was once a planet called Theia which crashed into the Earth at one point, creating the Moon.
Definition of a planet[change | change source]
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" is derived from the Greek word "planetes" - meaning wanderer.
in 2006 the International Astronomical Union (IAU) convened a Planet Definition Committee, deliberated, and ultimately reached consensus on a new definition of planet which leaves us with the eight planets we today consider to comprise our 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'.]"