I used to make fun of hypothetical Planet Nine (AKA Planet X). It is extremely far from the Sun. Based on gravitational effects on post-Neptune bodies, it is thought to be 2 to 4 times Earth’s diameter with a mass ten times Earth’s. Its orbit would be about 15,000 years (I do not plan to wait around for its return).
Scientific American suggests that the Sun may have captured it from a neighboring star. Other astronomers think that the Sun captured a rogue planet (planet floating in space independent of any star).
Write about this? You bet.
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