340 extrasolar planets have now been discovered. Time to think of a new way to name them.

Saturday, March 21, 2009

Remember this planet?

An article on space.com has elaborated in far better detail than I could on the problem facing us as we begin to discover more and more extrasolar planets and will soon have to find a new way to name / classify them. The problem (one problem) is that they are named in order of their discovery, but since the discovery of a planet has nothing to do with their location around their parent star, their order in their own solar system has nothing to do with the classification we give them, and ends up being a bit of a mess.

For a parallel example, imagine that another spacefaring race was observing our solar system, and began to discover planet after planet. Perhaps Jupiter would be easiest to discover thanks to its large mass, and Saturn is next. After that perhaps Mercury was seen thanks to its frequent transits in front of the Sun. Then Venus...oh, then Ouranos through a lucky break somehow, then Earth, then Mars, and finally Neptune, and the smaller bodies remain undiscovered.

So to sum up:
1 - Jupiter
2 - Saturn
3 - Mercury
4 - Venus
5 - Ouranos
6 - Earth
7 - Mars
8 - Neptune

Now the Solar System goes as follows, moving from Mercury outward: Sol-d, Sol-e, Sol-g, Sol-h, Sol-b, Sol-c, Sol-f, Sol-i. That's a bit of a mess.

The person that wrote the article proposes putting the orbital period after the name of a planet, so Earth would be Sol-364.(er...5?). Here's part of what he wrote (this is only a tiny part):
Similarly we would have 55 Cancri-2.9, 55 Cancri-14.6, 55 Cancri-44.3, 55 Cancri-260, and 55 Cancri-5218. Now why make such a fuss about this now (if writing an article about it can be considered a fuss)? Over 340 extrasolar planets have already been discovered and things have seemed to work out OK so far, right? The reason is because current space missions may soon discover thousands of additional planets as well as many more smaller planets than in already known planetary systems. Some space missions will be able to detect Earth- or even Mars-sized bodies. If our Solar System is typical in terms of having eight or more planets to a system, then there could be designations consisting of combinations of the letters b, c, d, e, f, g, h, and i! And all sorts of permutations on these could occur. We could get: (star name)- b, g, f, d, e, h, i, c or (star name)-e, d, i, b, h, c, f, or any other of the 46,233 possible combinations of eight letters taken one, two, three, and on up to eight ways at a time. The possible combinations go up as the factorial of the number of planets so things do not really get "bad" at one, two, three, four, or even five planets to a system (still only 120 possible combinations – on the order of learning the states of the US). But as one gets up into six or more planets to a star system the possible combinations really begin to take off.

And this is just the start of the fun. If we consider multiple star systems—where stars are usually designated by the capitols, A, B, C, etc.—we get situations where, for example, alpha Centauri A-b is a planet, while alpha Centauri B-a is a star. (The "a" designation would, of course, not be used unless a planet is discovered and then the "a" for the star is implied, using the present nomenclature.) Let's look at the 6-star system Castor (alpha Geminorum) where we actually already have the stellar components named Aa, Ab, Ba, Bb, Ca, and Cb. (The second components of close binaries are referred to with lower case letters in these cases.) These are each star names, but if a planet was discovered about star Ab it would, by the current nomenclature, be designated alpha Gem Ab-b, while a second planet would be alpha Gem Ab-c. Similarly, planets discovered around star Bb in order would be alpha Gem Bb-b, alpha Gem Bb-c, and so on, and planets discovered around alpha Gem Cb would be alpha Gem Cb-b, alpha Gem Cb-c, etc. So in this case alpha Gem Bb is a star, even though the first planet around the double star 16 Cygni B is 16 Cyg B-b. I guess the hyphen would be the only way to tell. Wouldn't it be easier, if three new planets are discovered around alpha Gem Bb, to have the designation be something more like alpha Gem Bb-12.3, alpha Gem Bb-20.2, and alpha Gem-43.6? Incidentally, double star systems are not rare—more than half of all stars are in binary systems.
Very complex, but it's a very happy situation. It's like starting to have more money than you know what to do with. Compare this to when we only had ten or so extrasolar planets we knew about and they were all boring hot Jupiters.

The next issue to come up will be whether Earth-like planets should have real names. It might be fun to want to name the first Earth-like planet we find Vulcan or something, but sometimes these planets turn out to be duds when later observations or calculations reveal that maybe this planet isn't so Earth-like at all - maybe the atmosphere is too thick or too thin and there's no chance that life could exist there (see Gliese 581 c for an example of a planet that turned out to be not quite as great as we thought), and we could end up with a planet with a really awesome name that really isn't all that awesome. Still, we should want to give planets that resemble ours to a certain extent a real name to make it easier to remember and keep in the public consciousness.

It's possible that momentum alone will result in a nickname being given to a planet like this; that's what will happen if there is enough excitement around the discovery. In that case we won't even need to worry about coming up with a name - the planet can have an official name and number, but the public may come up with its own name for the place, kind of like when the Canadian $2 coin first came out and there was debate over whether to call it the doubloon or the toonie or the twonie, the bearie, the deuce, or whatever else, but toonie stuck. This may be what will happen with a new planet that resembles our own.


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