Key Terms
- asteroid
- a stony or metallic object orbiting the Sun that is smaller than a major planet but that shows no evidence of an atmosphere or of other types of activity associated with comets
- comet
- a small body of icy and dusty matter that revolves about the Sun; when a comet comes near the Sun, some of its material vaporizes, forming a large head of tenuous gas and often a tail
- differentiation
- gravitational separation of materials of different density into layers in the interior of a planet or moon
- giant planet
- any of the planets Jupiter, Saturn, Uranus, and Neptune in our solar system, or planets of roughly that mass and composition in other planetary systems
- half-life
- time required for half of the radioactive atoms in a sample to disintegrate
- meteor
- a small piece of solid matter that enters Earth’s atmosphere and burns up, popularly called a shooting star because it is seen as a small flash of light
- meteorite
- a portion of a meteor that survives passage through an atmosphere and strikes the ground
- planetesimals
- objects, from tens to hundreds of kilometers in diameter, that formed in the solar nebula as an intermediate step between tiny grains and the larger planetary objects we see today; the comets and some asteroids may be leftover planetesimals
- radioactivity
- process by which certain kinds of atomic nuclei decay naturally, with the spontaneous emission of subatomic particles and gamma rays
- solar nebula
- the cloud of gas and dust from which the solar system formed
- terrestrial planet
- any of the planets Mercury, Venus, Earth, or Mars; sometimes the Moon is included in the list
This book was adapted from the following: Fraknoi, A., Morrison, D., & Wolff, S. C. (2016). Key Terms. In Astronomy. OpenStax. https://openstax.org/books/astronomy/pages/7-key-terms under a Creative Commons Attribution License 4.0
Access the entire book for free at https://openstax.org/books/astronomy/pages/1-introduction
