Young, Eliot Department of Space Studies, Southwest Research Institute, Boulder, Colorado.
Beatty, J. Kelly Senior Editor, "Sky and Telescope Magazine," Cambridge, Massachusetts.
Last reviewed:August 2018
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- Origins and taxonomy of the Sun's planets
- Definition of “planet”
- Minor bodies
- Possible unknown planets
- Planetary orbits and motions
- Planetary characteristics
- Planetary interiors
- Composition and phase changes
- Surface geology
- Impact cratering
- Catastrophic disruption and reaccretion
- Magnetic fields
- Characteristics of a dynamo
- Planetary atmospheres
- Related Primary Literature
- Additional Reading
A relatively large, rounded, celestial body that developed around a star and cannot sustain nuclear fusion reactors in its interior. Although humankind has known about the existence of planets in our solar system for centuries, recent discoveries have challenged a simple, conventional definition of planethood. These discoveries in the last few decades include “failed” stars called brown dwarfs, thousands of “exoplanets” beyond our solar system, including “rogue” exoplanets that do not orbit stars, as well as several new, planet-like bodies in the region beyond Pluto. Based on the richness displayed in our solar system and by exoplanets, planets are extremely diverse as a class of celestial object, existing across a wide range of masses, sizes, and compositions (Fig. 1). See also: Brown dwarf; Exoplanets; Solar system
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