Thursday, 22 November 2012

Words for worlds (1) - working past dwarves in space

Many people are likely aware of the IAU decision a few years back to create the new classification of dwarf planet, which reduced the 'full' planets in the solar system to eight and added five dwarves: Ceres, Pluto, Haumea, Makemake and Eris. Not everyone was happy, not least with the definition going beyond intrinsics to cover orbital clearing.

Beyond this issue, there's also the problem of division into comets and asteroids, bodies at Lagrangian points, the extra terms like 'minor planet', 'trojan' and 'centaur', transitions from gas giant to star and the challenge of reflecting relative size of moons and planets.

If there are more large worlds in the outermost reaches of our system and billions around other stars or travelling between them, these problems in classification could get worse.

To see if it can be helped based on existing terms, here's a simple two-term approach to core body type. The first word covers construction, the second mass. Here 'dwarf' shows only intrinsic aspects: its mass and hydrostatic equilibrium. Two words are coined: troid, from 'asteroid' and 'planetoid', for bodies of a mass below a dwarf, and mid, for stars and planets between the extremes, which seems fair but not too prosaic, has long roots and could be a nod to our geo- and heliocentric exceptionalism. The word 'planet' is optional.

1. ice / icy          1. troid
2. rock / rocky       2. dwarf
3. gas / gaseous      3. mid  
4. stellar            4. giant

As far as I can tell, it covers the core forms. Gamers will see immediately it's set up like two 1d4 tables so it could at least be used to generate locations for gaming. One or two purely conceptual results could make for interesting sci-fi experiments, like 'stellar troid'.

I think it's clear how it works. Using this approach, rather than teach children that Earth, Mars and Pluto have one or more 'moons', we'd say Earth is a mid with a dwarf, Mars is a mid with two troids and Pluto is a dwarf with five troids. It's still simplified, but less so.

With it our system gains lots of secondary dwarves, and if we're talking status that feels fair to worlds like Titan that may be home to terrestrial life's nearest neighbours. It sees our system become, as far as we know, one stellar mid, two gas giants, two ice giants, four rocky mids, I think 24 mainly rocky dwarves, and the oceans of ice and rock troids.

Various more extrinsic elements can be shown as extra terms, the most obvious being:

1. [primary / secondary / tertiary etc.]   1. [orbital / eccentric [dominant]]
                      2. Langrangian
                       3. interstellar

Halley's Comet then becomes a primary ice troid, or - more fully - a primary, eccentric, dominant ice troid. The adjective 'interstellar' still covers those so-called 'rogue' planets.

Who can see the problems with it?


Tallgeese said...

So a neutron star (diam. 12 km) might be classed as a stellar troid, or a stellar dwarf?

Porky said...

The situation is more interesting with stars because of the dramatic long-term variation. Here the naming is based on mass rather than volume so what might be called a mid using this approach could under current naming vary between a giant and dwarf over its lifetime, depending on where the mid-range is set. Of course, it could also vary under the new approach if it lost or gained enough mass. I've removed the mention of colour from the text to make it more clear what's going on. I can definitely see objections to this approach, but focusing on the mass does give a good reflection of the essence of events.

Given all of that, a neutron star might then just have the element 'neutron phase' added, to be called a 'neutron phase mid' for example. Another option is adding 'remnant' to the second list to allow the current 'stellar remnant' and classifying neutron stars there as now, with the current white dwarves and even black holes.

Tallgeese said...

I suppose either a black hole or neutron star could be classified as "dense stellar remnant", or respectively as troid stellar remnant and dwarf stellar remnant.

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