Scale of Pandora

[Nekxi]

I was wondering if anyone knew what the size of Pandora is in comparison to our Solar System.

When I was watching the movie I noticed the blue planet (which makes Pandora a moon) which is shown throughout the movie looked a lot like Jupiter. I think it actually is Jupiter, but then a blue version of it. (Gosh, they do love their blue ) If we were to say that it was Jupiter than finding out the scale is easy, but I'm not sure if it is. Because I've read somewhere else that it's supposed to be a moon in the facility of Alpha Centauri (4 light years away, which makes sense seeing as they spend 5 years to get there).

By the way, I know Pandora doesn't actually exist, but I'm just wondering about whether James Cameron has actually shared with us where he thought Pandora would be and what size it would be.

I made all nine planets of our solar system in scale, they're proudly hanging around my room. (Yay for heigh ceilings) But after seeing Avatar I really wanted to put Pandora up there as well.

Irayo ^_^

[Nìwotxkrr Tìyawn]

I can't recall the size of Pandora at the moment, I'm sure there was something on it though.

I'm assuming you mean 8 planets and one dwarf planet, Pluto is not worthy of being one of us. 

[Nekxi]

I still think Pluto's a planet. You can't let him be a planet for over 70 years and then take away his glory! That's just mean 

[Eywayä lì'u]

I still think Pluto's a planet. You can't let him be a planet for over 70 years and then take away his glory! That's just mean 

true! dwarfs are planets too!

[Nìwotxkrr Tìyawn]

The earth was "the center of the universe" for hundreds of years and we took that away too.

[Nekxi]

Yes, because it clearly isn't. We proved it isn't. But planet was a term given to Pluto and it should remain to be a planet. You can't scientifically prove that Pluto isn't a planet. You can choose to say it isn't, there's a choice there.

[Kerame Pxel Nume]

I still think Pluto's a planet. You can't let him be a planet for over 70 years and then take away his glory! That's just mean 

If you include Pluto into the set of planets, then you must declare a vast amount of other objects in our solar system as planets, too. Plutos properties shift it much more into the set of those objects, then into the common properties of what's called planets now. For example Pluto's orbital plane is strongly tilted against the orbits of the other planets. Also it has a high excentricity. It's got not enough mass for its own gravity shape it into a sphere. And last but not least, we know about bigger objects than Pluto, which would never had been called a planet.

On the other hand Pluto lent the name for this new class of objects between asteroids and planets: Plutoids.

This is just science: If an old idea conflicts with new discoveries, then you have to rethink it. This acceptance of new knowledge and discoveries is what segregates science from belief.

[Nekxi]

I know, I know... *sigh* But Pluto's something special and it should be names when we talk about our solar system. I'm not saying that we should start calling everything a planet, that'd be mad... I just think Pluto should be a planet. Just like our moon is called moon when we know there are billions of moons out there that we don't call moon. (That doesn't really make any sense... I'm just trying to say that language is a strange thing when it comes to naming certain things.)

[Nìwotxkrr Tìyawn]

The whole point of changing Pluto's status was because it was letting it stay a planet would be like saying 2+2=5.

[Eywayä lì'u]

The earth was "the center of the universe" for hundreds of years and we took that away too.

Yeah, but in that case the Earth had it coming. No-one can stay that self-centred and get away with it.

(Excuse the pun of self-centred there:) )

[Kerame Pxel Nume]

Just like our moon is called moon when we know there are billions of moons out there that we don't call moon. (That doesn't really make any sense...

There's a quite clear definition of what's a moon: A nonartificial object orbiting an object much larger then itself, orbiting the star(s) of a stellar system. Note that it's not clearly stating that a moon must orbit a planet. It can as well orbit a plutoid or even an asteroid.

The classification of objects is done by a - preferrably orthogonal - set of rules. Things are not named a planet, moon, plutoid, by arbitrary choice. They're classified as such by empirically derived rules. If the classification undergoes changes due to new data, then things eventually get called different.

[Tìng Eywatikìte'e]

Oh wow...ummm topic people? If we want to keep talking about pluto I'll move it to the general discussion board.

[Tsa'räni]

The ASG talks a little about this stuff.

Pandora is roughly Earth-sized (a little smaller) and the planet it orbits, Polyphemus, is smaller than Saturn.  It's the second of three gas giants orbiting Alpha Centauri A, the largest star (20% bigger than our own Sun) in the trinary Alpha Centauri system.

Beyond that, and a brief discussion about some of Polyphemus' other moons, we don't really know much.

[magne]

Gas giant is at the size of Saturn so a little smaller than Jupiter. Gravity on Pandora is 0.8 of earth so it would be a little smaller, this also depend on the amount of heavy material like metal in the core. Pandora is tidal locked like our moon so the same side always points against the planet, this will make the days long, I guess a week or more, this is also the explanation for all the bioluminescence. The part of Pandora we saw was towards the planet so you would bet pretty light nights anyway because of the planet-shine, the other side would have dark nights except from light reflected from the other moons.

[Nekxi]

I was wondering about how long their days would take, I was a little confused when I saw it was actually a moon. But I suppose that'd only be confusing to us who are used to 24 hours a day.

The whole point of changing Pluto's status was because it was letting it stay a planet would be like saying 2+2=5.

I know you can't technically call Pluto a planet, I'm just saying that in the case of Pluto I'm going to say 2+2=5. Not because I don't know what a planet is, or want to ignore that Pluto doesn't tick all the boxes, but because I think that after 76 years of being a planet you sort of deserve to stay one.

(Now back on topic )

Thank you all for your replies If Polyphemus is indeed the size of Saturn and Pandora slightly smaller than earth I'll definitely add them to my ceiling. (That sounds strange...) I love the way Polyphemus looks and it would be fun to paint, so I was kind of hoping for it to be at least smaller than Jupiter.

Thanks again for your replies

[Tsa'räni]

Make Polyphemus a little smaller than Saturn, as that's how the ASG describes it.  Literally, "Smaller than Saturn."  Saturn is the point of reference, though, so it must be reasonably close.

Oh, I meant to add it says Polyphemus orbits Alpha Centauri A at about the distance the Earth orbits the Sun.  Banding is described as more prominent than Saturn's but less spectacular than Jupiter's.  The great storm on Polyphemus is also larger than Jupiter's Great Red Spot, so keep that in mind while painting.

[Technowraith]

According to the ASG:

-Pandora is just slightly smaller than earth.
-It never gets completely dark at night, which does explain the bio-luminescence. Though on rare occasions, it does get completely dark.
-Gravity is .8G, or slightly less than earth's gravity.
-The atmosphere contains roughly the same percentage of oxygen as earth does, but the heavier gases like xenon are heavily present as well. This makes for a toxic atmosphere. The Exo-pack filters out the toxins though.
-The magnetic superconductive properties of unobtanium make for awe-inspiring formations like the vast stone arches and the floating hallelujah mountains.
-The land to water ratio is roughly the same as earth's. However, due to the much higher level of volcanism and plate tectonics, the landmasses are smaller, but more widespread.
-Polyphemus is a jupiter like planet that is about the size of Saturn. There is a prominent vortex storm like Jupiter's Great Red Spot.

There's other stuff about Pandora as well, so if you get a chance to get the Activist Survival Guide, i highly recomment it. It's a wealth of information.

[Tsu'roen]

Alpha Centauri A (ACA)
Mass                          1.100 M_☉ = 2.19 *10³⁰ kg
Radius                        1.227 R_☉
Surface gravity (log g)  4.30
Luminosity                   1.519 L_☉
Temperature                5790 K
Metallicity                   151% Sun
Rotation                     22 days
Age                           4.85 *10⁹ years

Earth  
Diameter             12756 km
Mass                  5.974 *10²⁴ kg
Surface Gravity    9.81 m/s²
Surface Pressure  1.014 *10⁵ Pa

Pandora (ASG p.6)
Diameter             11447 km
Mass                  4.301 *10²⁴ kg
Surface Gravity    7.85 m/s²
Surface Pressure  1.115 *10⁵ Pa

Polyphemus
located at the center of ACA's inhabitable zone (ASG p.13)
Therefore it's orbital radius must be:
   r = 1.25 AE = 187 *10⁶ km

Those data allow us to estimate the orbit period of Polyphemus to about 490 earth days:
Orbital radius                 r ~1.875 *10¹¹ m (inhabitable zone)
Solar Mass ACA             M ~2.19 *10³⁰ kg
Gravitational constant    G = 6.67428 *10^-11 m³ kg^-1 s^-2

   t_orbit = SQRT(4 * π² * r³ / G * M)
          = 42213845 s
          = 489 earth days
          = 1.34 earth years

That is the time in which Polyphemus rounds it's sun and most likely also the length of a Pandoran year


Several of Polyphemus' moons have a diameter larger than 6437 km (ASG p14)

"Some computer generated models of planetary formation predict the existence of terrestrial planets around both Alpha Centauri A and B.[72][73][74] Other models also suggested that formation of gas giant planets similar to Jupiter and Saturn remain unlikely because of the significant gravitational and angular momentum effects of this binary system.[75]"
(http://en.wikipedia.org/wiki/Alpha_Centauri#Theoretical_planets)

EDIT: added calculation of Pandoran year

[Nekxi]

Thank you all so much for this, I'm looking forward to painting now! Too bad I still got a lot of stuff to do, else I'd start making them now, but I think I'll have to wait till the next vacation. But I'm definitely going to add them to my planets (just need to find room) If you remind me, I'll post pictures if you guys want to see

Polyphemus is going to be a lot of fun to do, I had fun doing Jupiter too, especially the Great Red Spot.

Here are some pictures of what my room looks like now, for those who want to see

Spoiler

[Tsa'räni]

Wow, that's pretty cool!  Best of luck.