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inner planet

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noun Astronomy.
  1. any of the four planets closest to the sun: Mercury, Venus, Earth, or Mars.
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Compare outer planet.

Origin of inner planet

First recorded in 1950–55
Also called terrestrial planet.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for inner planet

inner planet

noun
  1. any of the planets Mercury, Venus, earth, and Mars, whose orbits lie inside the asteroid belt
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
inner planet in Science

inner planet

  1. Any of the four planets Mercury, Venus, Earth, and Mars, whose orbits lie nearest the Sun. The inner planets are of similar size and have high densities compared to the larger gas giants among the outer planets. They are composed mostly of rock and metal and are relatively slow to rotate, with solid surfaces, no rings, and few moons. Also called terrestrial planet Compare outer planet. See also inferior planet.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.