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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 (c) 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 elite 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.