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Thursday, July 24, 2008

The thirteenth planet?

The arrival of a new dwarf planet in the solar system last week reminded me of the fierce argument over the definition of "planet" that broke out in Prague in 2006, at a meeting of the International Astronomical Union.

If things had gone differently in Prague, the newcomer Makemake would now be considered in the same broad class as Earth or Jupiter, becoming the thirteenth planet of the solar system to be named.

At that meeting, the IAU started with a draft definition that included anything big enough for gravity to pull it into a roughly rounded shape, meaning that Pluto and similar largeish icy objects such as Makemake would have qualified. But the debate was eventually won by another camp, who argued that Pluto and its kind just formed a swarm of small debris that had never coalesced into planets proper. So today the solar system only has eight official planets, plus some dwarfs.

There are many astronomers and others who object to the IAU's decision in Prague, and would prefer to return to a definition that includes Pluto and probably all the other dwarf planets too. It is possible that they will get their way, changing the official definition at some future meeting of the IAU.

If that were to happen today, the thirteen named planets of the solar system would include Ceres, Eris and now Makemake. (I'm also counting the twin planet of Pluto-Charon as two. Although moons in general were sensibly excluded from planet status by the IAU's draft definition, Pluto's companion Charon was due to become half of a twin planet, for slightly technical reasons. It is not at present a dwarf planet; merely a moon.)

Perhaps there's no harm in having thirteen planets. Even the superstitious would soon be soothed, as astronomers will keep discovering more Pluto-like objects in the outer solar system. Eventually, we would probably have scores of planets.

It might be a problem, however, if you want to learn all their names and remember their order from the Sun.

Before 2006, there were plenty of mnemonics for remembering the then nine planets in order - such as:


Abbreviated versions are fine for today's eight. But with thirteen or more, how well would mnemonics work?

We would already have two Es and three Ms, and the situation would no doubt get worse, until people will be trying to remember which of the four Qs represents the newly discovered planet Quetzalcoatl.

The idea of "order out from the sun" would also become blurred, as the plutoids are liable to have overlapping orbits. (Though at least this would confuse some triskaidekaphobes.)

And it might be challenging to concoct a catchy phrase with the new letters.


... although I will reluctantly concede that someone else might be able to do better.

Stephen Battersby, New Scientist contributor

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Almost off the top of my head...

My Violin Exudes Music - Concertos Jostle Sonatas Unborn - Never Played - Charming Melodies Effortlessly

...offer me an inducement and I'll get the two initial letters of each planet name to start each word :)
...and the horse you rode in on for infecting my brain... (thank god I'm long over Googlewhacking)

Merciful Vera, Eagerly Manipulating Cerebro-spinal Junctions! Sacral Urgences Necessitated Placid Chiropractic Manipulation Erenow!

But what am I bid for three initial letters?
By Anonymous Anonymous on January 10, 2009 7:24 AM  
By Anonymous Anonymous on January 22, 2009 6:51 AM