Had Pluto itself not proved to be so spectacular when NASA’s New Horizons probe flew past last year, there can be no doubt that its large moon Charon would have won more admirers.
The remarkable moon has a mysterious dark-red stain over its north pole, called “Mordor Macula” by the New Horizons team – where Macula means “dark spot” and Mordor refers to the “black land” in Tolkien’s The Lord of the Rings. While many bodies in the solar system have polar caps or hoods of some sort, these are typically bright, due to reflective ice or frost of some kind, rather than dark. So what’s going on at Charon? A new study, published in Nature, has proposed an answer.