Moons

[Spyder]

Right you are, but, as I said most would not necessarily have atmospheres. The only one large enough to be called a planet seems to be in a binary planet symbiosis (gravitationally speaking) with Pluto supporting that if its too big, it becomes its own planet. But in all cases (I believe) the moons are Rock...no gas moons, no ice moons (probably are, but, this is further into Astronomy than I ventured ) and very few (comparatively) with atmospheres; all of which are around our largest gas giant.

In most cases the mass of the moon simply prohibits the ability to maintain an atmosphere...I have no idea why Jupiter's moons do...but, it takes a significant gravitational pull to hold any type of gas (atmosphere) in orbit and obviously they have it (with mother Jupiter's help, I'd guess).

But, back to the game....just build an atmosphere renewer on it and use it as a storage facility & shipyard. That is what I use all the Tiny planets for.



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Spyder, Chairman of the Arachnid Consortium

[Suicide Junkie]

There is no way that a planet could help a moon hold on to atmosphere. Jupiter's moons are just big, thats all.

Tiny planets would almost all be 'none' atmospheres (as well as moons)

Small planets would usually have atmospheres, and some of the biggest moons would be small planet size.

Assuming Earth-mars-venus type planets are the small end of medium sized (SE4 homeworld size)

[apache]

Um, you guys better review basic astronomy. Those 4 moons with atmospheres are not all around Jupiter. Io and Ganymede are, but Titan orbits Saturn, and Triton orbits Neptune.
Also, it is wrong to call Pluto's moon, Charon, a planet, because a planet is a large body orbiting a star. Moons orbit planets. And in general, anything that orbits something else is a satellite.
And there are ice moons in our solar system. Europa (Jupiter) is the most famous, since it is believed to be able to support life under its ice layer.

[Spyder]

No argument with either of you guys...however, I would like to know what's under that ice on Europa....rock maybe? or, is it just one big ball of ice? If its rock, does that make it an ICE planet/moon or a ROCK planet/moon?

And, as for Charon, it is a planet-sized moon which probably affects Pluto nearly as much as Pluto affects it....kinda like a binary star system...soooo...is it a planet with a moon, or two planets? The question is even more valid if there is question of its orbit...it was mentioned that some think it has its own orbit...<shrug>

The idea I was originally was trying to point out was that moons don't usually have enough mass to hold an atmosphere. That is probably why, in the game, all moons are rock with no atmosphere (that and the sake of simplicity).


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Spyder, Chairman of the Arachnid Consortium

[This message has been edited by Spyder (edited 01 March 2001).]

[Suicide Junkie]

Actually, half the moons are ice in SE4.

In fact, most moons are ice, but only if you're a Rock/None race.

[This message has been edited by suicide_junkie (edited 01 March 2001).]

[Shepherd]

Here's some numbers for you, guys.

Earth's moon has a 1738 km radius, making it a little over one-fourth the width of the earth. It's a rocky moon with a high density (around 3300 kg/m^3), giving it a surface gravity of about 1/6th G.

Ganymede (Jupiter), Callisto (Jupiter), and Titan (Saturn) are all icy moons, meaning that their average density is rather low, around 1500 kg/m^3. They're all around the same size, about 2600 km in radius, making them about 40% the width of Earth. Since they have approximately the same density and size, it's not surprising they have similar gravities, all about 1/7th of G. Note that although these moons have similar stats, they're pretty different otherwise; Titan has a methane atmosphere, and Europa may be liquid water under an icy shell.

While we're on Jupiter, let's not forget Io. This is a rocky moon about the same size as Earth's moon, but a little denser. Io's gravity is about 1/5.5 ths of G. Of course, Io being a *molten* rocky moon studded with volcanoes doesn't make it very habitable.

Finally we have Triton, the true gem of our solar system as far as moons go. Triton is about the same size as Earth's Moon, but is very dense, making it a rocky moon, although its surface is covered with ice. Triton's gravity is 0.29 G -- which sounds pretty comfortable. Unfortunately, at a surface temperature of 38 K (-235 Celsius, or -391 F), its atmosphere is mostly hydrogen and if it rains at all, it's raining liquid helium. So I'd have to say its planetary conditions are 'Unpleasant'.

The distinguishing feature between icy and rocky worlds seems to be their density, which has direct effects on their gravity, surface structure, and magnetic field. Icy moons are low gravity with no mag field. Rocky moons are higher gravity, with a mag field possible.

All data taken or calculated from the tables in my astrophysics book. If you find I've made a mistake somewhere, let me know!

[This message has been edited by Shepherd (edited 01 March 2001).]

[apache]

Well, by definition, rock is ice, a solid form of some silicate most likely. The truth is that ice planets are really planets that have things normally not frozen on Earth that are frozen on that planet. Ammonia, Methane, water, etc. are all stuff that is normally seen unfrozen on earth and most other planets in the system. But ice planets for whatever reason have these gasses/liquids actually frozen to, and acting as the surface. Europa has an ice surface, and some form of liquid ocean underneath. Under that, of course, is a solid basin of some sort.