Description: A planet is defined by the International Astronomical Union as a celestial body in orbit around a star or the remnant of a star, that is large enough to be nearly round in shape by its own gravitational force, but not massive enough for thermonuclear fusion to ever occur in its core. It must also be large enough for its gravity to remove other objects that pass close to its orbit around the star. Therefore, they are cold bodies (as compared to stars) that shine in the visible band only by the light reflected from their stars but they do emit light at infrared wavelengths. In our Solar System, eight planets orbit around the Sun. Planets may be basically rocky objects, such as the inner planets – Mercury, Venus, Earth, and Mars – or primarily liquid and gas with a small solid core like the outer planets – Jupiter, Saturn, Uranus, and Neptune. Planets outside the Solar System are called extrasolar planets or exoplanets for short.

Related Terms:

• Earth
• Exoplanet
• Gas Giant
• Giant Planet
• Ice Giant
• International Astronomical Union
• Jupiter
• Mars
• Mercury
• Neptune
• Nuclear Fusion
• Outer Planets
• Saturn
• Solar System
• Terrestrial Planet
• Uranus
• Venus

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".