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	Archive through July 28, 2007	25		07/29 09:35pm

Mike Strain

Technically, the Hydrans evolved on an Ice Giant, not a Gas Giant. Jupiter and Saturn are Gas Giants (are composed primarily of gasses: Hydrogen and Helium). Uranus and Neptune are Ice Giants (are composed primarily of Methane Ice, Ammonia Ice and Water Ice). Seriously. Uranus and Neptune are both about 1/6 rock/metal, about 2/3 ices, and about 1/6 gas (Hydrogen + Helium). Unfortunately the Wikipedia article kinda sucks, so I'll write up a bit more about their formation.

By Dale Lloyd Fields (Dylkha) on Sunday, July 29, 2007 - 04:36 pm: Edit

Planet Formation [basically a lead-in as to what the differences between Gas and Ice Giant mean]

Here is the best idea we have for how planets form. There are three main facts that intertwine in planet formation:

1) The disk the planets form out of is mostly composed of Hydrogen and Helium and a tiny bit of everything else (around the Sun, 98% was H and He). Every part of the disk has the same elements as every other part of the disk.

2) Planets form from solid stuff sticking together.

3) The temperature of the disk decreases the further you go from the Sun.

First one outcome of 3) is that matter is in different states in different parts of the disk. Close in it is very hot and everything is in a gaseous state (hotter than 2000 K). A little bit further out, things like metals and silicates (rock) can exist as a solid, but things like H2O are still in a gaseous state. Going out even further it is cool enough that metals and silicates are solid, but so too are things like H2O. In all parts of the proto-Solar System Hydrogen and Helium (again, 98% of the matter) remain as a gas.

Now link 3) to 2). In the inner solar system only rocks and metals are solid. Therefore when planets form close to a star, they are only formed out of rock and metal. Further out, rock/metal is a solid, and so are ices* so planets that form further out in a star system are made up of a mixture of rock/metal and ice. Consequently, since there are more total solids, outer planets tend to get more massive.

Now there is a special threshold in a planet's growth (happens around 15 times the mass of the Earth). When you only have a little gravity you can only hold onto the heavy gasses (things like O2 and N2 and CO2 and H2O). When you have a lot of gravity you can hold onto light gasses (things like Hydrogen and Helium). Once a planet grows (by solid stuff sticking together) up to about 15 times the mass of the Earth) it has enough gravity to hold onto Hydrogen and Helium. Link this back to 1). Most of the material in a disk where planets are forming is Hydrogen and Helium. If a planet gets to 15 Earth masses, it can start to grow by grabbing all this gas around it. It starts slowly, but each bit of Hydrogen and Helium it grabs means the planet has more mass and more total gravity. And more gravity means it pulls in Hydrogen and Helium faster. Which means more mass and more gravity and more pulling in of neighboring gasses. After a while a big planet (which started out as pure solid stuff) can have more gas than solids! The only thing that stops a planet's growth is that the proto-Sun eventually becomes the Full Fledged Sun and blows away all the remaining gases in the Solar System.

How does this relate to Ice Giants and Gas Giants? Jupiter and Saturn and Uranus and Neptune all started as big hunks of rock/metal and ice. All passed the threshold that meant they could start to suck in the surrounding Hydrogen and Helium. The only difference is that Jupiter and Saturn passed the threshold early and so had a lot of time to suck in so much gas they became most gas (Gas Giants) while Uranus and Neptune got a late start and were only able to suck in a little bit of gas before the Sun cut them off. Uranus and Neptune would have become Gas Giants if they had more time, but were stopped while they were still mostly rock/metal and ice. So they remain Ice Giants.

In fact, Jupiter, Saturn, Uranus and Neptune all have about the same amount of solid stuff: about 15-20 times the mass of the Earth in rock/metal and ices.

* Ice to an astronomer is a "solid volatile." Basically the solid form of something that can easily evaporate. SiO2 (rock) would not be a volatile, but H2O (water) or CH4 (methane) would. So there are water ices, methane ices, and ammonia ices (the most common ones).

By Mike Strain (Evilmike) on Sunday, July 29, 2007 - 08:08 pm: Edit

I know about basic planetology.

Regardless of whether its an Ice or Gas Giant, the premise stays the same. If they 'evolved' on either, they would be radically different from the way they are portrayed in SFB. Their thought processes would be, literally, incomprehensible.

I think the Uthiki, in C5, are gas-giant floaters, and Burnside had them pretty mysterious (plus the fact that the Andro's singled them out for an especially THOROUGH extermination).

By Dale Lloyd Fields (Dylkha) on Sunday, July 29, 2007 - 08:40 pm: Edit

Mike Strain

I don't think so. Gas and Ice Giants are sufficiently different that very different types of life are possible for both. Ice Giants have a "surface" where the density gradiant spikes. Now, it isn't as strong a discontinuity as on Earth's, but it is still sufficient to allow the evolution of "walking" as a form of locomotion. The extremely high pressure in the depths of a Gas Giant means gas has aquired the consistency of a plastic solid so they have no such layer with a sharp density gradiant. The only such efficient locomotion method there would be floaters/swimmers. A life form developing on the surface of an Ice Giant would be more like us than one developing inside a Gas Giant (well, speaking in terms of evolutionary psychology). I don't see the major differences.

I do agree that they are more likely to have different psychologies than the rest of the alpha species. I would love it if the NO species of the SFU could be developed with differing psychologies like Cherryh's Atevi or Mahendo'sat. But I don't see them being different to the point of incomprehensibility like the the Jgd-Il-Jagd of Traveller or the Zang of Uplift. I do think the Hydrans have abnormally high metabolism rates for a cryogenic species, but at some point you have to do what you can to make a species playable (imagine if the Hydrans could only fire every 8 impulses).

Since I guess I'm not seeing your point, what do you think the primary environmental differences would be that would result in truly alien psychology?

By Michael C. Grafton (Mike_Grafton) on Sunday, July 29, 2007 - 09:35 pm: Edit

I don't think the background supports the idea of a Hydran from a 15 g planet. They aren't as strong as the gorns...

By Mike Strain (Evilmike) on Monday, July 30, 2007 - 10:04 pm: Edit

....or dense enough to shrug off phaser blasts.....