On Wednesday, the International Astronomical Union officially announced the names of features on Pluto’s moon Charon. The features were revealed when the New Horizons probe shot past Pluto and its five moons, and the names were provided by the public. While astronomers working on the New Horizons data had been using the monikers provisionally, the IAU’s announcement makes them formal designations that will be used in all scientific publications about Charon.
While four of Pluto’s moons are so small that New Horizons captured them as pixellated blobs, Charon is quite different. And, while all moons and their planets orbit a common center of gravity, usually the size difference is large enough that the center of gravity resides inside the planet. The Pluto-Charon system is the big exception, as the size difference between the two is small enough that Pluto orbits a point that’s located outside the dwarf planet’s radius. That makes Charon one of the largest bodies among the icy worlds of the Kuiper Belt, and it’s the second largest body we’ve gotten a detailed look at.
While Charon doesn’t seem to be as dynamic as Pluto, it does have many notable features, including large peaks, deep canyons, and massive craters, as well as a dusting of material that has evaporated off Pluto. In 2015, the public was invited to give these names; the New Horizons team informally adopted a number of suggestions, and the IAU has made them official. The theme of the names centers around travel and exploration, often (but not always) with a connection to the underworld or the deeps.
The mountains named honored storytellers, including Stanley Kubrick and Arthur C. Clarke, who collaborated on the film and book. Octavia Butler also picked up the honor of having Butler Mons named after her.
The moon’s canyons were named after boats. Argo Chasm is named after the boat that gave the Argonauts of myth their name; Mandjet Chasma is one of the boats that carries the Egyptian god Ra across the sky. But perhaps the most evocative story is the one behind Caleuche Chasma, which is named after a boat that supposedly prowls the shores off Chile, collecting the dead who ride on the boat forever after.
The craters of Charon have picked up names from literature and legend. These include recent explorers, like Nemo of the Jules Verne tale, Dorothy of the , and Pirx, who was featured in the writing of Stanislaw Lem. Folktales from the Arab world provide the name for Nasreddin Crater, and a Russian epic that’s centuries old gives us Sadko Crater; Revati Crater picks up its name from the Hindu Mahabharata.
There are plenty of other features left to name, some of which already have names in informal use (looking at you, Mordor Macula), so this should be viewed as part of an ongoing process. There’s a chance it’ll still be ongoing as New Horizons approaches its next target, a Kuiper Belt object it should reach in 2019.