inner planet

American  

[in-er plan-it] / ˈɪn ər ˈplæn ɪt /

noun

Astronomy.

1. any of the planets in our solar system whose orbits lie between the sun and the asteroid belt, namely, Mercury, Venus, Earth, and Mars, all of which are terrestrial planets.

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inner planet British  

noun

1. any of the planets Mercury, Venus, earth, and Mars, whose orbits lie inside the asteroid belt

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inner planet Scientific  

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.

2. Also called terrestrial planet

3. Compare outer planet See also inferior planet

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Etymology

Origin of inner planet

First recorded in 1950–55

Example Sentences

They first refined measurements of a previously known inner planet, GJ 251 b, which completes an orbit every 14 days.

From Science Daily • Nov. 13, 2025

The orbits of the three known planets showed a 3/2 resonance between each neighboring pair: For every three times the inner planet orbits, the outer neighbor orbits twice.

From Science Magazine • Nov. 29, 2023

The exoplanets are huge: the inner planet is 14 times as massive as Jupiter and the outer one is 6 times as massive.

From Nature • Jul. 21, 2020

Could the same greenhouse effect that would torch the inner planet thaw the outer one and make it livable?

From New York Times • Dec. 3, 2011

Meadows began to play inner planet combinations that occasionally paid, though at short odds.

From Fee of the Frontier by Fyfe, Horace Brown