‘HD 11964 d’ by Any Other Name

What to call the planets we find beyond our solar system?

We don’t call people by their Social Security numbers. We don’t hail them by their birth dates. We call them by their names. We don’t refer to cities by their latitude and longitude. We use their names. Mountains have names, so do rivers, states, provinces. We may employ coordinates to help us locate such places, but that’s not how we talk about them. The planets in our solar system—the major and many of the minor ones—have names.

Shouldn’t we extend the courtesy to planets that orbit other stars?

At present, astronomers deploy alphanumeric designations such as kappa CrB b, HD 11977 b, HD 11964 d, and TrES-1 b for extrasolar planets, also called exoplanets, with the first part of the designation referring to the star and the lowercase letters referring to the planet, or planets: b, c, d, and so on. Astronomer Beth Biller calls it “the telephone number system.” There are no official common names for such worlds, however, according to a policy set by the International Astronomical Union (IAU) and one that makes sense—if they remain only objects of research for astronomers. But for the rest of us, our likely interest in these planets suggests that we need ways to speak comfortably about them.

It’s worth remembering that not so long ago astronomers debated whether our solar system was the only one in the entire universe. Clearly it’s not, and as we move closer to finding planets like our own, what today seems an arcane matter will loom: What do we call these new worlds?

While the IAU is content to stick with alphanumeric designations—this system is clear enough for cataloging—informal names have nonetheless cropped up. Gliese 581 c has been nicknamed Ymir, after a Norse god from whose corpse the universe was constructed. A planet designated 51 Pegasi b is sometimes called Bellerophon, after the rider of the steed Pegasus, who, alas, ticked off Zeus; you can guess how that went. HD 209458 b is sometimes called Osiris, for the Egyptian god of the dead.

To observers such as I, a writer who stargazes and eagerly keeps up with news of exoplanet research, and doubtless to the scientifically engaged public at large, the current situation is most unsatisfactory. Alphanumerics matter to astronomers the way Latin genus-species names matter to botanists or ornithologists. Curiously, though, whenever I’ve been in the field with plant lovers or birders, I’ve noticed that they are able to move seamlessly between scientific names and common names, as if to concede that laypeople aren’t experts and that common names have other things to commend them, such as a sense of connection (through the story a name calls to mind) and a kind of poetry (through the sheer pleasure of language). Latin names can have these too, of course, but at a remove for most of us.


Those astronomers who have been nicknaming exoplanets understand, as Biller says, that “planets . . . have a very deep resonance for people.” The impulse to name them is just part of who we are, part of our evolutionary need to point and to utter. And, interestingly, the nicknames so far evoke mythological beings, which itself suggests that learning about these worlds renews our wonder at the vast forces and epic time scales of the cosmos, just as mythological stories do.

Critics of assigning names to exoplanets worry that as search techniques and telescope technologies advance we’ll have too few names for too many worlds. “We will be finding hundreds if not thousands of new planets in the next decade or two,” exoplanet astronomer Alan Boss says. “Do we really want to give them all names?” There are “literally billions” of planets in the Milky Way waiting for discovery, he points out.

Pioneering exoplanet hunter Geoff Marcy disagrees with the astronomers who are content with alphanumerics. Although he helped to set up the formal designation system, Marcy contends that at least some of these extrasolar worlds deserve common names. Planets “within a mere tens of light-years” will be the ones photographed first by orbiting telescopes, he predicts. “Later, we’ll explore them with robotic probes. Surely, the nearest planets will be the first destinations of any spacefaring humans. These nearest planetary systems deserve names, if only because they orbit our future.”

Astronomer Alfred Vidal-Majar says that exoplanets within 1,000 parsecs (about 3,300 light-years) of Earth should be named, as well as any others that generate a great deal of research interest, regardless of distance.

I offer another criterion: Name exoplanets that are new Earths. Imagine the inspiration to science-fiction writers and readers dreaming of travel to an actual world, an actual other Earth, with an actual name! Yet there’s more to this, I think, than helping the next Arthur
C. Clarke.

At a time when our home world is under increased siege by the toxicity of convenience—with rising temperatures and rates of extinction, with freakish weather and shortages of food—perhaps knowing that this is not the only world with water and photosynthesis and breathable air, we’ll be reminded of why they are such exquisite gifts, why they deserve our respect and stewardship. Far from making our planet seem less special, finding and naming similar worlds will help us see Earth as part of a cosmic family and a place worth protecting from our own worst impulses, even as we gaze at a beckoning sky.

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Christopher Cokinos is the author of The Underneath, a poetry collection, and co-editor of Beyond Earth’s Edge: The Poetry of Spaceflight. He’s working on a book about the Moon and has recently published poetry and prose in The Chariton Review and Sky & Telescope.


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