Planet X

短语

未知行星；冥外行星

发音

/ˈplænɪt ɛks/

释义与例句

name
  1. 1.

    A hypothetical planet in the Solar system, beyond the currently known outermost planet. (The term was applied to Eris for a short while, when Pluto was still considered the ninth planet.)

    X行星

    天文
  2. 2.

    A theoretical planet responsible for reported gravitational perturbations of Neptune's orbit. (This was initially believed to be Pluto. The reported perturbations were an error.)

    废旧 天文
  3. 3.

    A theoretical planet responsible for observed gravitational perturbations of Uranus' orbit. (This planet was discovered and is now known as Neptune.)

    废旧 天文

词源

X represents an unknown as opposed to the Roman numeral for 10 (initially, Planet X would have been the ninth planet).

来源：wiktionary