Aspiring lunar explorers, take heed — any newly discovered ridges on the Moon must be named for a geoscientist. If you want to name a landform on Saturn’s satellite Titan, you’d better be a fantasy or science fiction fan: Mountains and plains on the lake-covered moon are styled after places in Tolkien’s Middle Earth and Frank Herbert’s “Dune” series. Almost everything on Io, the eruptive moon of Jupiter, must have a name associated with fire, volcanoes, or Dante’s “Inferno.”
So decrees the International Astronomical Union, the official arbiter of planetary and satellite nomenclature since 1919. As ever more powerful telescopes and ambitious new robotic missions add to the identified real estate of the solar system, the IAU’s brilliant, byzantine and sometimes marvelously nerdy naming guidelines help bring order to our crowded skies.
The IAU’s rules are in the news this month after the Carnegie Institution for Science announced it needed help naming several moons of Jupiter discovered last year. Carnegie astronomer Scott Sheppard, who spotted the new moons using a giant telescope in Chile, said suggestions should be tweeted to the handle @JupiterLunacy using a #NameJupitersMoons hashtag.
Protocols for planetary nomenclature being what they are, Sheppard can only consider names that meet a few key criteria:
It must come from a character in Greek or Roman mythology who was either a descendant or lover of the god known as Zeus (in Greek) or Jupiter (Latin). It must be 16 characters or fewer, preferably one word. It can’t be offensive, too commercial or closely tied to any political, military or religious activities of the past 100 years. It can’t belong to a living person and can’t be too similar to the name of any existing moons or asteroids. If the moon in question is prograde (it circles in the same direction as its planet rotates) the name must end in an “a.” If it is retrograde (circling in the opposite direction), the name must end in an “e.”
Easy peasy, right?
“Jupiter is one of the more restrictive ones,” Sheppard said.
Gareth Williams, an astronomer at the Harvard Smithsonian Center for Astrophysics who serves on the IAU working groups for planetary system and small bodies nomenclature, said these stringent guidelines are necessary to avoid confusion in the study of the cosmos. Before the union came along in the early 20th century, the solar system was a mess.
Weird names, or 3 names
Political fights and international disputes occasionally broke out over the names of new planets; Uranus was very nearly called “George’s star” after England’s King George III awarded an annual stipend and plush new digs in Windsor Castle to the planet’s discoverer, William Herschel. Improvements to telescopes that made it possible to identify the inhabitants of the asteroid belt resulted in scores of new rocky bodies being discovered every year. (One scientist derisively called them “vermin of the sky.”) Few researchers took the time to cross-check whether their supposed “discovery” had actually been seen before. Maps of Mars and the moon were similarly rife with conflicts. A given crater or dome could have three different names — and a given name might describe two entirely different objects.
It wasn’t until 1913 that anyone published a definitive list of every known feature on the moon — then the solar system’s most-studied object. Work by Mary Adela Blagg, an English astronomer who meticulously tracked each new discovery and mismatched name, led to the creation of the IAU’s first formal list of lunar landmarks in 1935. Two decades later, the organization published a similar guide to Martian topography, drawing mostly on maps developed by astronomers over the past century.
With the advent of the Space Age, “people were making new discoveries by the bucketload,” Williams said. It was far more than one person could keep track of, so the IAU established a Working Group for Planetary System Nomenclature to oversee the naming process.
When the first images are beamed back from a mission to a new celestial body, the spacecraft team behind the encounter typically proposes categories and themes for naming the landforms they observe, said Rita Schulz, chairwoman of the WGPSN.
After NASA’s New Horizons probe flew past Pluto in 2015, for example, scientists on the team and at the IAU devised a naming scheme focused on stories of the underworld and voyages of discovery. They agreed that mountains on the planet would be named for historic explorers while dark spots and plains on its moon, Charon, could commemorate the destinations of fictional space expeditions. As a result, we have the Tenzing Montes on Pluto — 20,000-foot-tall ice mountains named for Nepalese mountaineer Tenzing Norgay — and a macula, or dark spot, on Charon called “Mordor.” (Space is full of Lord of the Rings references.)
Once themes are decided, anyone can suggest a name for a new body or feature so long as he or she can demonstrate it is scientifically useful. New suggestions are reviewed by the relevant task group and the members of the overall working group and, once approved, are published in the Gazetteer of Planetary Nomenclature.
“If you know your mythology … you can immediately tell what body it’s on and what type (of feature) it is,” Williams said.
Lately, space scientists have needed to learn more than just Greek and Roman myth. As secretary for the Working Group for Small Body Nomenclature, Williams said he has sought to diversify the themes asteroids and other small objects to reflect the “changing life experiences of the astronomers that are naming them.” He is particularly proud of asteroids named for popular musicians. “Not the sort of teeny bop noise that you get,” he said, “but people who are as worthy as the great classical composers,” such as Jimi Hendrix, Billie Holiday and David Bowie.