The Discovery of Planets Outside of the Solar System
So far, so good. But then along came the planet hunters and things started to go awry.
A couple of the early exoplanet discoveries, in 1996, were around the stars τ Bootis (tau) and υ Andromedae (upsilon). These planets were cataloged as τ Boo b and υ And b. The letter “a" is, in effect, not used as it signifies the star, a bit of a strange decision as the star is already identified by it Bayer/Flamsteed/HD etc catalog number. A further three planets were discovered in Andromeda, which came to be listed as υ And c, υ And d and υ And e. Now it should have been obvious at this early stage that there was room for confusion: “α Con B" could easily be misread for “α Con b" and vice versa, and if a planet is discovered around “α Con A" then it becomes “α Con Ab," which does rather sound like a binary star system!
If you think that is confusing then read on.
The planet hunters obviously decided to use Bayer notation for planets discovered around the brighter stars. Hence, when a planet was found to be orbiting the brightest star in Piscis Australis, it was obviously going to be called a PsA b. Except it wasn’t. They called it after the star’s proper name, Fomalhaut b (pronounced foe-ma-low). Oh, and just to muddy the celestial waters further, Piscis Australis is also known as Piscis Austrinus.
With ρ1 Cancri (rho) the planet hunters were on safer ground as the star does not have a proper name. The five planets in orbit around the star could logically be cataloged as ρ1 Cnc b, c, d, e and f. But that would have been too easy! Instead the Flamsteed number was used and so they became 55 Cnc b, c, d, e and f.
Perhaps we are on safer ground with μ Arae (mu), a star so far south that Flamsteed could not catalog it, and nor does it have a proper name. But no, the four planets around μ Arae have been listed as HD 160691 b,c,d and e using the Henry Draper catalog.
Okay, the Henry Draper Catalog covers far more stars than Bayer or Flamsteed so perhaps we should use that instead? It makes some sort of sense, doesn’t it? Hence, the single detected planet around HD 204961 in Grus will be called HD 204961 b. No chance! It is listed as GJ 832 b from yet another catalog, Gliese-Jahreiss. Then there is ι Horologii b (iota) which could have been HD 17051 b or even GJ 108 b but is, instead, HR 810 b, one of just two entries from the Harvard Revised Catalog.
With around 1,400 confirmed or suspected planets the list of confusing names seems to go on forever. Wouldn’t you think that someone could co-ordinate the naming and cataloguing?