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How Do New Planets Get Their Names?

Sorry, Planet McPlanetface: Asteroids, moons and other celestial bodies go through a strict set of international naming guidelines

Shortly after the announcement of the TRAPPIST-1 system, NASA crowdsourced its Twitter followers for possible planet names. The actual process of naming new planets, however, is a bit more involved. (NASA / Spitzer Space Telescope)
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Last month, an international team of astronomers made a stunning announcement: they’d just found a system of seven planets, including several potentially habitable ones, orbiting a nearby dwarf star. In the ensuing mania, NASA jokingly asked its Twitter followers to suggest some names for the exoplanets, sparking the trending Twitter hashtag #7Namesfor7NewPlanets. Space Twitter, being nothing if not creative, was quick to deliver the goods.

NASA followers made hundreds of suggestions, ranging from silly to satirical to reverent. There were the seven dwarves of Snow White (Bashful, Doc, Dopey, Happy, Sleepy, Sneezy and Grumpy); the seven characters from the TV show Friends (Rachel, Monica, Phoebe, Chandler, Joey, Ross and Janice); and, more seriously, the surnames of the seven fallen astronauts of the 1986 Challenger mission (Scobee, Smith, McNair, Onizuka, Resnik, Jarvis and McAuliffe).

But what actually goes into naming a new planet or other celestial object? Are there public contests where people can vote for names like Boaty McBoatface, or are naming privileges held by a select few? And can someone really buy the right to name a crater on Mars starting at $5, as the space-funding company Uwingu advertises on its website?

As fun as getting to name your own crater sounds, it doesn’t actually work like that. "It's a rather careful process," says Gareth Williams, an astronomer at the Harvard-Smithsonian Center for Astrophysics. Williams should know: In addition to his work at Harvard-Smithsonian, he serves as associate director of the International Astronomical Union's Minor Planet Center, and sits on several committees that carry out the work of sorting through potential planet names.

Formed nearly a century ago to encourage international cooperation in the burgeoning field of astronomy, the IAU now regulates asteroid names—along with planets, minor planets, comets, moons and geographical features on planets and moons. This involves a carefully regulated, months-long process of proposals and committees to ensure that no newly discovered celestial object is double-named, and that no offensive or overly silly names make their way onto our astronomical maps.

In 1919, when the IAU was formed, such a naming system was badly needed. While convention had dictated that comets were named after their discoverer—most of the major planets besides Earth had long ago been named by the Romans—Williams says asteroids presented a particularly confusing situation. As telescope technology quickly advanced in the wake of the Industrial Revolution, astronomers worldwide would often publish small citations in journals of lists of asteroids they'd discovered.

But these objects were rarely cross-checked to ensure they hadn’t been already spotted and named, and there were no consistent patterns of naming. Thus this “freeform” naming system may have led to scientific confusion, he says. "It took quite a while for things to sort of calm down," Williams says. Under the IAU, astronomers had to piece together records and, in some cases, rediscover asteroids.

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Planetary classics like Jupiter, Mars, Venus, Mercury and Saturn (shown here) were named thousands of years after Greek and Roman gods and goddesses. Uranus, Neptune and Pluto (now a dwarf planet), despite being discovered much later after the invention of the telescope, were named in a similar vein. (NASA / Voyager 2)

Like asteroids, astronomers only began to discover stars beyond the few thousand visible to the naked eye in the late 19th- and early 20th centuries. They quickly became a problem, as astronomers and publishers immediately began compiling their own star catalogues, many of which used unique names for the same stars, Williams says.

Even today, stars remain beyond the scope of the IAU: though the body has weighed in to formally approve names for a few hundred well-known stars, the star-naming universe is otherwise still wide open. (For example, various star catalogs name the same yellow dwarf star in the constellation Ursa Major 47 Ursae Majoris, FK5 1282, GC 15087, Gilese 407, HR 4277 and SAO 43557.)

According to Williams, these fiery bodies present an example of the confusion that would exist without the standardization of the IAU. "The IAU is trying to keep the solar system from becoming like the stellar designations," he says. But how?

That’s where the careful process comes in. Once an initial discovery is reported to the IAU, Williams says, the organization assigns the object a temporary name while astronomers confirm the discovery, and ensure it hasn't already been found. Then the object is assigned a permanent number—similar to an ISBN for books—which can always be used to reference it. Only then can a name be proposed.

For comets, IAU follows the time-honored tradition that the first two discoverers get to have their surnames attached to the object. (Contrast this with the taxonomic process of naming new species, where it’s generally discouraged to name a species after yourself. Scientists are expected to do their own research on whether a species is really new, follow an internationally agreed-upon code in picking a name, and then make the name official by publishing a description in a peer-reviewed journal.)

For asteroids, things can get more creative: The discoverers of an asteroid are allowed to propose any kind of name they feel like, Williams says, as long as it falls within a few basic guidelines.

First, the name should not be too long. It should also be pronounceable, different from any other existing names and not offensive. Names related to businesses are also forbidden (sorry, Elon Musk) and pet names are discouraged (sorry, Fluffy). Proposers may draw on political and military figures and events, but only 100 years after the person's death or after the event occurred. Eventually, a committee that Williams sits on rules on the merits of the proposed names. An asteroid gains its official name when it's published in one of the IAU's monthly Minor Planets Circulars.

Want some tips on naming your very own celestial body? Try asking amateur astronomer Gary Hug. A food scientist and machinist by day, Hug has spent many of his nights over the past two decades discovering new objects in the sky. With his homemade high-tech backyard observatory in Kansas, Hug has discovered roughly 300 asteroids and one comet. One suggestion he makes is to avoid hubris in picking a name. While the comet 178P/Hug-Bell was named after Hug and his fellow amateur astronomer Graham Bell, Hug says there’s “kind of a code” among asteroid discoverers not to name them after themselves.

However, Hug’s favorite source of names for all those asteroids he’s found is his friends and family, especially the ones still alive to receive the honor. He named his first discovery after his wife, an honor he says she initially wasn’t enthusiastic about. “Oh boy, a big fat rock in space,” Hug recalls her saying (he says she later came to appreciate the gesture). He managed to name an asteroid for his mother before she died, and many of his friends have had their names enshrined in the sky as well.

“To me, it's something I can do for other people,” Hugs says. Many of the easy-to-spot asteroids have now been discovered, Hug says, so he’s only been able to name a handful in recent years. “15-20 years ago, you could swing a dead cat by its tail and hit an asteroid,” Hug jokes.

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Asteroid 21 Lutetia, photographed by the Rosetta spacecraft, is the largest asteroid visited by a probe. The asteroid was named by French astronomer Hermann Goldschmidt, who spotted it from the balcony of his apartment in Paris in 1852; "Lutetia" is the latin name for Paris. Its number reflects that it being the 21st asteroid discovered. (NASA)

With further advances in space technology, the IAU has seen its mission to name newly discovered celestial bodies and space features expand. Today we have powerful space telescopes that can zoom in on the planets of the solar system and beyond. We’ve flown satellites right next to Pluto and the outer planets. We’ve sent a rover to explore Mars. As the geography of other worlds becomes nearly as clear to us as Earth's, we end up faced with a lot more geographical features to name.

"The need to name features on other bodies beside the Moon is a very recent feature of the naming process," Williams says.

To help corral this process, the IAU has decided to follow a system of themes that the IAU has over the years developed for the geographic features of planets and moons. Many of these themes are related to classical Greek and Roman gods, in keeping with our Solar System, but this is by no means is universal. The valleys of Mercury, for example, are all named after abandoned cities and towns (Angkor Vallis, Caral Vallis, Timgad Vallis), while the craters of Europa pay homage to Celtic heroes and gods (Rhiannon, Maeve, Elathan).

The entire naming process can take years, Williams says, which is he why the IAU discourages astronomers from announcing their proposed names before they're approved. However, this hasn't stopped the team behind NASA's New Horizons satellite that flew by Pluto in 2015 from releasing a map of "informal" names for many of the dwarf planet's features. "There's no guarantee [they] will be approved," Williams says.

Naming exoplanets is the IAU's newest task. The first exoplanet was discovered only in 1992, and since then, these objects have only had names derived from the names of their stars. However, as more were discovered, the IAU decided to open up this naming to the wishes of average people with a contest. In 2015, the organization launched an online contest allowing people to vote on names for a few dozen exoplanets. Last month, the IAU officially approved names for 17 exoplanets from the contest, including Thunder Bay, Brevardastro and Kagura.

“The IAU is delighted to see the involvement of amateur astronomers and of the public in the naming of newly discovered worlds, which, in many respects, puts our own little planet in perspective,” said IAU General Secretary Piero Benvenuti after the announcement.

It's unclear if the IAU will conduct more public contests like this, Williams says, and he is quick to point out that any other people claiming to have the rights to name planets and their features are in the wrong. The for-profit company Uwingu, for example, allows people to "name" craters on Mars for a fee. But by international agreements of astronomers, Williams says, any names chosen by groups other than the IAU are not allowed on official astronomical maps. "The IAU takes a very dim view of this," he says.

Out of the hundreds of name proposals he has seen working with the IAU, Williams' favorites are always "the witty ones." Names that play off the object's permanent number are particular favorites, he says—such as Asteroid 8191, which was named "Mersenne" after the French mathematician Marin Mersenne, who famously discovered a series of unique prime numbers. The number 8191, it turns out, is one of the Mersenne primes.

Another example is Asteroid 2037, which is named Tripaxeptalis. That nonsense word sounds like the phrase "tri-pax-sept-alice," which is a kind of math problem: The number 2037 is three times 679, the number of asteroid Pax, and seven times the number 291, the number of the asteroid Alice.

Of course, there are many bland names for asteroids and planetary features out there, Williams admits. But to him, that just makes the good ones more memorable. "You have to have a lot of mundane names for the gems to stick out," he says.

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