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Planet Nine
Reference material by Wiktionary contributors. This retains its source identity and is not 411 news reporting.
English
thumb|Artist's impression of Planet Nine eclipsing the central Milky Way, with the Sun in the distance; Neptune's orbit is shown as a small ellipse around the Sun.
Alternative forms
en Planet 9 Planet IX
Proper noun
planet Nine
en astronomy A theoretical ninth planet in the Solar system, the gravitational effects of which would explain the improbable orbital configuration of a group of trans-Neptunian objects that orbit mostly beyond the Kuiper belt.