It’s not just Jack who names the planets

Gliese 667c. Connected to, but definitely not, Ganymede in Lyra's naming system. Photo (c) Nasa.

An artist’s impres­sion of Gliese 667c. Connected to, but def­in­itely not, Ganymede in Lyra’s nam­ing sys­tem. Photo © Nasa.

Wladimir Lyra’s fol­low­ing in the foot­steps of Jack in his arXiv paper Naming the extra­solar plan­ets. Currently plan­ets are tagged after their par­ent star, so if we found a planet around α Ceti, it would be called α Ceti b. The b in lower case is used for the first planet to be found, c for the second and so on. a is not used to avoid con­fus­ing a planet with a star. Unfortunately in the case of some double stars a cap­ital B would be used for the second star, so names could get con­fus­ing. So why not name the plan­ets? Lyra gives a couple of reas­ons why he thinks this would be a good idea. One is that names like Bacchus are more beau­ti­ful than names like HD 128311. One person’s beauty is another person’s mess, so I’m not con­vinced by this. However, he also pro­poses that names for extra­solar plan­ets aren’t just dec­or­at­ive, there’s also the Copernican prin­ciple.

“Mercury — Venus — Earth — Mars is a sequence of equals. Sol b — Sol c — Earth — Sol d would impli­citly imply that the Earth is spe­cial in some way.” For this reason, Lyra argues that nam­ing the extra­solar plan­ets is neces­sary to avoid the impres­sion that the Solar sys­tem is spe­cial. I’m more per­suaded by this, but it misses an obvi­ous point — the Solar sys­tem is spe­cial. It’s where I am, it’s where all humans are and it’s where they’ll be for the fore­see­able future.

My biggest objec­tion to his paper was that I’m not sure how help­ful it would be. Even deal­ing with ancient his­tor­i­ans I tend to avoid clas­sical names for stars, except in a few cases. Vindemiatrix or Protrygetor, names for the same star in Latin or Greek aren’t as help­ful as ε Virginis, because ε Virginis gives the reader a clue as to where in the sky they’ll find the star. Similarly I can see why Lyra would give the name Bellerophon to a planet, but I wouldn’t find it as help­ful as 51 Pegasi b. The IAU have said there are likely to be too many extra-solar plan­ets to name. The prob­lem isn’t likely to be the sup­ply of names, which is a shame as Lyra solves that neatly. It’s mem­or­ising what goes where.

For that reason I’d prefer a Bayer style sys­tem so in the ε Eridani sys­tem you could num­ber the plan­ets from inner­most orbit to outer I, II, III and so on. It sounds simple, but it won’t work. The first star you find in a sys­tem is likely to be the most massive, not the closest to the star. Using this sys­tem you wouldn’t be able to num­ber plan­ets until you dis­covered every planet in the sys­tem. Every time you dis­covered a new planet you’d have to renum­ber the sys­tem, caus­ing havoc when you try and use older papers for com­par­ison which use a dif­fer­ent num­ber­ing, or else have a data­base of each system’s num­ber order for plan­ets. Another solu­tion would be to num­ber plan­ets in order of mass, but that’s not likely to be fool-proof either.

Another pos­sib­il­ity would be a Bayer style des­ig­na­tion which embed­ded inform­a­tion about a planet in its name. So Gliese 876 d would be Gliese 876 p1.9379, p for planet and the num­ber fol­low­ing it is the orbital period. This too has flaws though as orbital peri­ods can be cal­cu­lated from assumed masses and may be revised in the future. A pos­sible solu­tion would be to only give names to the min­imum num­ber of sig­ni­fic­ant fig­ures neces­sary. In the Gliese 876 sys­tem that would give plan­ets names p60 for b, p30 for c and p2 for d. The exact fig­ures may change, but the rel­at­ive order of peri­ods would mean you would have a fair chance of identi­fy­ing a planet named in a early paper on the sys­tem at some time in the future.

Things do change and cata­strophes occur upset­ting sys­tems. Hybrid names like 55 Cancri p 5000 Argive might help track ref­er­ences to 55 Cancri d as papers accrue over the years. I’ll cheer­fully con­cede a name like Althaea for planet 16 Cygni Bb (the first star dis­covered orbit­ing 16 Cygni B, hence the Bb) would be easier to under­stand. Ultimately though I think the prob­lem is not the names, or their alloc­a­tion. It’s what the names are used for.

The vis­ible plan­ets had names because they were vis­ible, dis­tinct­ive and needed names. Uranus and Neptune also got names because there were so few plan­ets so more names were not men­tally tax­ing. Lyra points out that aster­oids have names. This is true, but when 1 Ceres and 2 Pallas were dis­covered it wasn’t anti­cip­ated that 2309 Mr Spock would be join­ing them. These days a cata­logue num­ber is essen­tial to identify an aster­oid, the name is not so import­ant. The same can be said of comets. Originally they were named by the date they appeared. After the dis­cov­ery of the peri­od­icity of comets by Halley, they began to be named, but these days comets also bear cata­logue num­bers. So who will use these planet names?

Ontic dump:

A name for some­thing that car­ries inform­a­tion about it. e.g. An example Stewart and Cohen give is if you know what an arrow and a head are, you can work out what an arrow­head is, even if you haven’t come across that word before.

For the vast major­ity of the extra­solar plan­ets their exist­ence will only be noted by astro­nomers, much like stars and galax­ies today. While names may be beau­ti­ful, astro­nomers don’t seem to use them for stars, nore for many galax­ies. Likewise names may add some­thing of value to extra­solar plan­ets, but equally use of them on a reg­u­lar basis could be cum­ber­some. Names have most value where things are not eas­ily cat­egor­ised, like the rocks on Mars. Mythological names have the fur­ther dis­ad­vant­age in that they are purely abstract rather than ontic dumps. An ontic dump would have the double use of not only labelling a planet, but giv­ing some inform­a­tion about it. Bayer clas­si­fic­a­tions, when used as names, are usu­ally ontic dumps, as are the cur­rent extra­solar planet names. This mat­ters in the Lyra name sys­tem as some of the names actu­ally run counter to Graeco-Roman cosmology.

As an example the name Dike is asso­ci­ated with a planet found in Libra. In clas­sical myth­o­logy Dike, Justice, is in fact an aspect of Virgo. Libra was ori­gin­ally the Claws of Scorpio. Once the method is explained then the Lyra sys­tem makes sense, but it would be counter-intuitive in some cases for any­one with a know­ledge of clas­sical myth­o­logy. Another example would be that Amphitrite, the nymph wooed by Poseidon with the aid of Delphinus is not asso­ci­ated with con­stel­la­tion Delphinus. If names are to be used then a method divorced from the myth­o­lo­gic­ally laden mean­ings of the mod­ern con­stel­la­tions might pre­vent con­fu­sion. That’s why I think Stuart’s sug­ges­tion to use names from all sorts of lit­er­at­ure has a lot of merit. Though there’s some­thing to be said for Exoplanetology’s sug­ges­tion too.

Ultimately the names for the extra­solar plan­ets will be names that have mean­ing to the com­munity of reg­u­lar users. In the past clas­sical ref­er­ences were com­mon cul­ture shared by aca­dem­ics in all European uni­ver­sit­ies. Those days have gone. I could bemoan the decline in clas­sics, after all I’m an ancient his­tor­ian. But there’s also a lot to cel­eb­rate about the cre­ation of aca­demic links out­side the Euro-American com­munity. If names are adop­ted hope­fully they’ll reflect that it’s not just the num­ber of worlds that has grown, but also the astro­nom­ical com­munity from a small élite at the start of the 20th cen­tury to the world­wide exchange of inform­a­tion and ideas that we have today.

If you’re won­der­ing who Jack is, there a video on YouTube.


When he's not tired, fixing his car or caught in train delays, Alun Salt works part-time for the Annals of Botany weblog. His PhD was in ancient science at the University of Leicester, but he doesn't know Richard III.

2 Responses

  1. GaryCorby says:

    Why not do it as star name / year / let­ter? So for example alpha Ceti 2009a? The prob­lem with names is we will run out of sens­ible ones very quickly and end up nam­ing per­fectly inno­cent plan­ets after minor celebrit­ies. The prob­lem with only a let­ter or num­ber is it implies a mean­ing­ful order which doesn’t exist. Important extra­sol­ars will inev­it­ably get their own names by pop­u­lar usage at the time they become important.

  2. Laura says:

    Do you really want to know why this is a ter­rible idea? Ask an immunologist.