It's Time to Play "Name That Exoplanet!"

Just as nature abhors a vacuum, humans can’t stand things not having names. 

As soon as naturalists spy a never-before-seen creature or explorers stumble upon a new land, they set about christening their discoveries. This undeniable urge has led to some, shall we say, issues over the naming of exoplanets, the worlds beyond our solar system. 

For the past 22 years, ever since finding the first exoplanets, researchers have generally preferred alphanumeric scientific designations blessed by the International Astronomical Union (IAU) — we’re talking exoplanetary handles like UScoCTIO 108b and TrES-3b. But now that scientists are finding thousands of new worlds, the populace is rising up to demand more prosaic names.

The ruckus over popular exoplanetary names finally reached a boiling point last year. The startup company Uwingu (meaning “sky” in Swahili), composed of several prominent astronomers — and IAU members — publicly thumbed its nose at the IAU. It held a contest to name the closest exoplanet, designated (by the IAU, of course) as Alpha Centauri Bb. The contest doubled as a fundraiser for space exploration, research and education, charging $4.99 for name nominations and 99 cents for votes, and yielded such names as Rakhat and Caleo. 

The IAU denounced the contest as a “name-selling campaign,” saying such projects “have no bearing on the official naming process.” Uwingu bristled and responded with fightin’ words: “The IAU has no purview — informal or official — to control popular naming of bodies in the sky or features on them.” 

The IAU, feeling the heat, is now working to involve the public while retaining its role as the authoritative astronomical name-giver. But the war-of-words between exoplanetary naming camps isn’t over. (The public naming of craters on Mars spurred more sniping between the organizations in February.) As IAU General Secretary Thierry Montmerle understatedly put it: “Planet naming is a very emotional issue.” 

The desire just to name these things already will only increase. Thousands to tens of thousands of new planets will be rolling in, and the verification of the first truly Earth-like alien planet — which will beg for a real name — is also likely right around the corner. 

The IAU is holding off on the urge to name. “I think we should not rush into the planet-naming process,” says Montmerle. “We have to be careful not to name everything now precisely because future generations might have different ideas.” 

Alan Stern, CEO of Uwingu and principal investigator for NASA’s New Horizons mission to Pluto, disagrees. “It’s much like the opportunity our ancestors had when they were coming across the continents — they got to name everything,” says Stern. “With exoplanets, it’s the people of the 21st century who are going to do this job.” 

So how will this end? Here is a run-through of popular naming schemes, starting with today’s ad hoc designation system. It’s not all serious business: Some worlds could sport the names of fictional Star Wars planets or — who knows — even your mother’s uncle’s pet iguana. Either way, it’ll be fun to see what happens.

How it works:  In the current system, one of three things determines an exoplanet’s name: how it was found, the tool that found it or who found it. “Every method and team has its own internal naming system,” says the IAU’s Montmerle. This approach has led to an inconsistent designation scheme, which he jokingly calls “organized chaos.”

The 1995 discovery of the first exoplanet around a sunlike star set a precedent. That star, officially called 51 Pegasi, is the root of the exoplanet’s name. To catalog it, the planet-finding astronomers added a lowercase b, after other classification schemes that deem the star itself A. Astronomers used the “wobble” method to detect 51 Pegasi b, in which the planet’s gravitational tug alters its star’s light. Most exoplanets found in this way simply retain their star’s official name, followed by a lowercase letter. Other exoplanet names likewise derived from star names include the HD series, such as the super-Earth HD 85512 b, and the Gliese and GJ planets. 

Exoplanet hunters also use the transit method, which scours stars for the tiny shadows of crossing planets, to find new worlds. Because many of those stars don’t have an official name yet, any exoplanetary quarry found this way gets named after the observing instrument or spacecraft. NASA’s Kepler space telescope has bagged nearly a thousand transiting exoplanets; the European Space Agency’s defunct CoRoT (COnvection ROtation and planetary Transits) has scores to its credit. Resulting names include Kepler-22b and CoRoT-7b. From the ground, meanwhile, the SuperWASP project, using observatories in the Canary Islands and South Africa, has yielded several dozen WASP exoplanets. 

But wait, there’s more! The tiny Persian Gulf nation of Qatar, for instance, funds an exoplanet search project that’s nabbed a couple of worlds, dubbed Qatar-1b and Qatar-2b. Meanwhile, the citizen science Planet Hunters project has notched a planet on its belt: PH1b. What was that about organized chaos?

The pros: Some so-called exoplanetologists embrace the scientific designations despite their quirks. “I’m personally very happy with the current system,” says Massachusetts Institute of Technology astrophysicist and planetary scientist Sara Seager. She cites its functional universality to scientists around the world; anyone can go and look up an exoplanet by its basic, agreed-upon designation. NASA’s Bill Borucki, Kepler principal investigator, agrees: “The scientific name is a good name — it’s simple, it’s short.” 

The cons: For others, the designations fail to inspire. Wladimir Lyra, a planetary scientist at the Jet Propulsion Laboratory in Pasadena, Calif., says the names are boring and don’t resonate with non-scientist audiences. Lyra is tired of being asked at public lectures about what these worlds are called, and “the only thing I had to give them were names that look like car plates and phone numbers.”

How it works:  Lyra has proposed expanding on the Greek and Roman mythological motif used in our solar system. In a 2009 paper, he suggested Greco-Roman names for almost all 403 exoplanets then known. Lyra chose monikers associated with the myths of the exoplanet host star’s constellation. For example, in the constellation Hercules, exoplanets would be named after the Greek hero’s 12 labors, which included capturing the giant deer Cerenytis (now 14 Her b) and killing the man-eating birds of Stymphalia (HD 155358 c). 

The pros: This method jibes with the naming styles we’re all accustomed to for the solar system’s worlds. “I was trying to go back to classical tradition,” Lyra says. 

The cons: We’ll run out soon — there are only so many mythological Greco-Roman names. And most have already been attached to the approximately 15,000 named asteroids in the solar system. But names are frequently repeated in astronomy anyway (Atlas is a moon of Saturn as well as a star in the Pleiades), and Lyra says such repetition is not as problematic as you might think. “You have Memphis in Tennessee and Memphis in Egypt. They’re both Memphis, but you don’t confuse them,” he says. 

Lyra suggests that not every exoplanet needs a handle beyond its scientific designation, given that the Milky Way alone likely boasts billions of worlds. Instead, only the nearest and dearest should be blessed with a name, he says: “I think we should name planets up to a boundary, set arbitrarily at 100 light-years or so.” But perhaps the biggest issue with the Greco-Roman naming scheme, Lyra admits and Montmerle agrees, is its inherent cultural bias. 

How it works: While Greco-Roman names might have been the way of the past, expanding into other mythologies could be the way of the future. For instance, exoplanets in constellations named after birds, such as Aquila the Eagle, might draw a similar avian treatment, with names like the mythological Chinese birds Jingwie and Peng. Alternatively, non-classical constellation names could also serve as wellsprings of mythological characters. The Sumerians, for example, named the constellation of Orion after their hero Gilgamesh, whose epic poem remains well read.

The pros: Why shouldn’t other cultures’ mythologies get a go? “I would be quite happy with the internationalization of the system to include other mythologies,” Lyra says. The final version of his paper, published in 2010 in the Bulletin of the Brazilian Astronomical Society, recommended non-Western mythological names for the additional exoplanets discovered since his arXiv draft. 

The IAU has started down this road as well. The organization re-christened Kuiper Belt object 2005 FY9 — a dwarf planet out past Neptune’s orbit — as Makemake in 2008, after a god of the Rapanui people native to Easter Island. Haumea, another dwarf planet, is named for a Hawaiian goddess of childbirth. Montemerle sees it as a potentially promising exoplanet naming convention. Until recently, he says, “names have been entirely dominated by Western culture and mythology. I would personally advocate taking this extraordinary opportunity of naming exoplanets to really represent the world culture.”

The cons: Invoking other mythologies could prove offensive. After all, today’s mythology is yesterday’s religion. “We should be very careful not to give the name of a god being actively worshipped,” says Montmerle. Mythology also could be limiting. Montmerle thinks we can be more creative. Exoplanets could be named for “people who have contributed to the enhancement of humankind — musicians or writers or painters or artists,” he says. Indeed, within the solar system, the IAU has established many outside-the-mythology-box naming conventions, such as craters on Mercury after deceased artists, and Shakespearean characters for Uranus’s moons. 

How it works: Besides a casual name, what if exoplanets had something like a taxonomical species name, mirroring biology’s kingdom-phylum-class-order-genus-species arrangement? Exoplanets’ current scientific designations — and proposed mythological names, for that matter — reveal nothing about their actual characteristics. 

Eva Plávalová, an astronomer at the Slovak Academy of Sciences in Bratislava, proposed in a 2011 paper a five-parameter taxonomy for exoplanets. Take the exoplanet 55 Cancri e — in Plavalova’s system it would be 9E-1.8R1, and here’s what that tells you (hang on, it’s pretty dense): 

The first parameter, “9E” is the planet’s mass, expressed in equivalent masses of solar system planets. Scaling from the pipsqueak to the gargantuan, M is for Mercury, E for Earth, N for Neptune, and J for Jupiter. So, this exoplanet has nine times Earth’s mass. Its 1.8 refers to the distance from its host star in sun-Earth distance units, given in base 10 logarithm form. For the third parameter, Plávalová devised four temperature classes: F represents freezing; W, water; G, gaseous; and R, somewhat humorously, is roasters — so 9E-1.8R1 is a hot, hot place. The fourth parameter is eccentricity — how much a planet’s orbit deviates from a perfect circle. It ranges from 0 to 1, like 0.057; Plávalová simply round the first decimal place, so 0.057 becomes just 1. The final possible taxonomical parameter is an exoplanet’s surface attributes, whereby ‘t’ signals terrestrial, ‘g,’ gaseous, and ‘i,’ ice; since we’ve never imaged the surface of any exoplanet, this fifth term remains blank for 55 Cancri e when it’s renamed 9E-1.8R1. (For those keeping score at home, Earth comes out as “1E-0W0t”.)

The pros: Just by looking at the exoplanet’s taxonomic species name, someone in the know would glean loads of information. Plus, it’d bring order to the current chaos of planetary designations. 

The cons: Don’t expect the idea to catch fire with the public – if 55 Cancri e is already a mouthful, good luck with 9E-1.8R1. In rare cases, duplicate taxonomical names could crop up, too. Plávalová realizes such a scheme is at best a long shot, but she’s hopeful fellow scientists consider it over today’s willy-nilly designations. “When you write a paper, you have to name the planet something,” Plávalová says. “It’s important to establish some classification.”

How it works: Although not everything’s been worked out, the main idea is that the general public or a group, guided by public feedback, approves of popular names for exoplanets for use alongside the original scientific designations. The respective leaders of the IAU and Uwingu, the major players in this arena, hold very different views on the matter. 

“We have to be very selective on the quality of the names,” Montmerle says. “The names should stand the test of time and not be your neighbor’s girlfriend’s name, but something that reflects something really deep within humanity.” Montmerle envisions everyday folks working with local astronomy clubs to submit thoughtful name proposals with broad appeal. The professional astronomers of the IAU Commission in charge of exoplanets would then review the suggestions and ratify the most appropriate or best-sounding. Even something pop-cultural like “Alderaan” from Star Wars could end up passing muster (assuming no trademark issues). “I see no big problem with that,” Montmerle says. “Star Wars, after all, is part of our culture.”

Uwingu’s Stern frowns upon this sort of bureaucracy. Instead, he says that naming should operate on a “first come, first serve” basis. “We feel it should be open to the people of the Earth to name exoplanets anything they like as long as it’s not pejorative, prejudiced, insulting or profane,” Stern says. Given the likely billions of exoplanets in the Milky Way alone, Stern does not feel that any one planet has to be sanctified with some hallowed name. Family members, coworkers, sports teams and commercial brands are all fair game. “If United Airlines wants a planet, let them have it,” he says. “Get over it. They have one in a hundred billion.” To prove the point, the winning entry in Uwingu’s Alpha Centauri Bb contest last year was “Albertus Alauda,” a Latinized version of a participant’s grandfather’s name. 

Montmerle says the IAU will continue working toward a solution, but he cautions: “I think we are still a far cry from having found any valid method.”

The pros: Informal names for astronomical objects are common and have stood alongside official IAU names. Examples include the Milky Way for our galaxy, Mount Sharp for the official Aeolis Mons on Mars and Polaris for a star with dozens of recognized astronomical names, including, as most people would call it, the “north star.” Popular naming would engage the public with astronomy in a whole new way, Stern argues, “and I think that’s crazy exciting.”

The cons: Public naming involves the risk of a vocal few “winning” to the disgust of virtually everyone else. Uwingu’s monetary model has also drawn criticism. “When you combine anyone naming planets by whatever way they want and actually paying to do that, you end up with bad names,” says Lyra. “I think naming should be given to a committee that cares about nomenclature.” 

NASA’s Borucki is also skeptical of public naming, especially of potentially habitable worlds. “Leave the scientific name as is,” he says, “until the people on that planet tell you what they want it to be called.”

The First Popular Exoplanet Names?

Uwingu’s Alen Stern believes the exoplanet naming issue will ultimately resolve itself through “usage” — whatever names the public simply begins using in aggregate will stick, regardless of any official approval or contest. Assuming myriad media articles and Wikipedia serve as a good source on societal group-think, clear exoplanet name examples already stand out:

Osiris  An Egyptian god of the afterlife and the unofficial alias for the “hot” Jupiter HD 209458 b. 

Tatooine  A commonly used epithet for Kepler-16b, the first confirmed circumbinary planet, meaning it orbits two suns like Luke Skywalker’s fictional desert world from Star Wars.

Methuselah  The eldest of the known exoplanets, aged 12.7 billion years, PSR B1620-26 b circles a pulsar and a white dwarf, two incredibly old stars. Its namesake is the oldest person to have ever lived, according to Biblical lore. 

Bellerophon  The nickname for 51 Pegasi b, the first planet found around a sunlike star, named after the Greek mythological hero who rode the winged horse Pegasus, which by no coincidence is the constellation of the host star.

Zarmina University of California, Santa Cruz professor Steven S. Vogt led the team that has claimed the detection of the unconfirmed and potentially habitable world Gliese 581 g. The team refers to it informally after Vogt’s wife. 

[This article originally appeared in print as "What's in a Name?"]