noun
outer planet
Astronomical term for planets beyond the asteroid belt: Jupiter, Saturn, Uranus, Neptune. Contrasts with 内惑星 (inner planets).
木星は外惑星の一つです。
Jupiter is one of the outer planets.
内惑星 refers to the inner planets (Mercury, Venus, Earth, Mars), while 外惑星 refers to the outer planets.
Compound of 外 (outside) + 惑星 (planet).