Which planet has the largest moon system in comparison to its size?
Quick Answer
Pluto’s moon Charon is unusually large relative to Pluto, with a diameter about half of Pluto’s. The pair is often described as a binary system.
The Full Story
Pluto and Charon form one of the strangest planet-moon systems in the Solar System because Charon is so large relative to Pluto. Charon’s diameter is about 1,212 kilometers, roughly half that of Pluto. Their barycenter lies outside Pluto’s surface, which is why many astronomers describe them as a binary pair rather than a simple planet and moon. The system was discovered in 1978 and studied closely by New Horizons in 2015. This size relationship is far more extreme than that of Earth and the Moon.
Key Facts
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"Pluto and Charon are so closely matched they behave like a double world."