Can anybody find a mistake in this Avatar photo?

[traciutaustin]

My professor showed us this photo from Avatar and asked if anybody could find a mistake within it, but I can't see it! Can you tell what is wrong with it?
http://img291.imageshack.us/img291/6331/pandoraavatar.jpg

The mass closest to us is Pandora and there is a small thing off to the right which I think is a satellite.

 

[turbo]

Curvature of terminator in planet doesn't match that curvature in the terminator of the moon too well. Pandora's terminator is straighter.

 

[Filip Larsen]

I must admit I cannot see anything wrong with the terminator. Event though animators often make some pretty non-realistic stuff, I assume the image is rendered by a computer with a light placed more or less where the sun should be (or by using a parallel light source).

However, if this was a real planet and moon, I would be surprised to find a moon at what appears to be well within the Roche-limit of the planet.

 

[berkeman]

I don't know what a terminator is, but the light for the planet and the moon looks to be coming from different places. The moon's lighting is almost horizontal, and the planet's lighting seems to be coming down more at like a 45 degree angle...

 

[Borek]

Terminator is a huge guy with metal skeleton, played by Schwarzenegger.

http://en.wikipedia.org/wiki/Terminator_(solar)

But that's strange - I agree with Filip that the scene was most likely rendered and why it looks the way it looks is beyond me.

 

[Filip Larsen]

I just made a quick mock up in my CAD program with two spheres and a parallel light source, and when I compare with that, the terminator on the picture suddenly look wrong to me, so I would like to retract my earlier statement

Also, in my mock-up the moon ended up being at a distance from the center of the planet of around 1.5 times the radius of the planet which is very close.

 

[Jonathan Scott]

There's also what looks like reflected sunlight in the lower left, suggesting that the sun is in a different direction from that implied by the terminator.

 

[DaveC426913]

Never mind the terminator, that moon is well within the parent planet's Roche limit. (Oh, filip beat me to it.)

Actually, I'll shoot myself in the foot before anyone else does. We cannot even guess how far away the moon is from the planet. That's a factor of optics, which we do not know.

Here's a pic of Dione in front of saturn:

http://wallpapers-diq.net/wallpapers/49/Ringside_with_Dione%2C_Saturn%27s_Icy_Moon.jpg

 

[DaveC426913]

...I agree with Filip that the scene was most likely rendered...

As opposed to what? On site in orbit around a blue gas giant?

 

[traciutaustin]

My professor just posted the answer, in case anybody was interested!

The "mistake" in the picture of Pandora and its parent, giant planet is this: the giant planet is rendered in deep blue colors, like the colors of Uranus and Neptune in our Solar System. The parent planet clearly is a giant planet like Jupiter, with storms and other cloud features correctly shown. Pandora is one of its moons, as correctly described in the movie.
The problem is this: Pandora and its parent planet are very much in the habitable zone around the star. The temperature on Pandora is comfortably warm. This is OK, as I said in class: it is to be expected that some Jupiter-sized planets will have migrated inward into the habitable zones around their stars. Then their satellites will be plausible places to look for life, and Pandora is portrayed as such a world. All OK. But this means that the temperatures on the giant planet will be warm, too, warmer, in fact, than on Jupiter. The blue color of Uranus and Neptune is created, as I said in class, but methane absorption in the atmosphere. But methane would be very abundant only at the low temperatures found far out from the star, way, WAY beyond the habitable zone.
The composition of such a giant planet is not much in doubt, and there is no trick to change the composition to favor blue colors. So the planet should be colored more or less like Jupiter or even redder.
Arguably, it should also have a stormier surface than is shown,
but I won't make that a requirement for the answer.

 

[DaveC426913]

Pandora and its parent planet are very much in the habitable zone around the star. The temperature on Pandora is comfortably warm.

Is your professor confident that Pandora cannot be comfortably warm for any reason other than its proximity to its sun? There are planets in our solar system that exhibit uncharacteristically warm temperatures even though they are orbiting gas giants.

 

[Farquezy]

hey, i remember when the geysers on one of saturns moons were observed, Michio Kaku said that planets that are very far from the sun, if they are large enough, can keep their moons warm because of something about their gravity
He didnt go much in depth
but he said its plausible to find life on moons of planets so far away from the sun

Maybe you should ask your prof about that
here it is


yeah your prof was wrong, you should ask him what he thinks about what Michio Kaku said, i believe Michio over your prof any day lol

 

[Who Am I]

No, his professor wasn't wrong. To sustain such abundant plant life, you will need the same amount of starlight that we get from our sun, if not more.

The atmosphere isn't going to warm up from tidal forces either. The core will because it is constantly strained.

 

[Borek]

To sustain such abundant plant life, you will need the same amount of starlight that we get from our sun, if not more.

This is assuming "life as we know it". This is not a bad assumption, but it has to be spelt out before using.

 

[DaveC426913]

This is assuming "life as we know it". This is not a bad assumption, but it has to be spelt out before using.

No assuming necessary. We saw the life on Avatar; it was definitely as we know it.

 

[pseudophonist]

When arguing fiction, don't forget to use all the resources. Pandora kept warm by the magic of Unobtainium, anyone? (did anyone else cringe when they mentioned that name?)

 

[Borek]

No assuming necessary. We saw the life on Avatar; it was definitely as we know it.

You have been not paying attention. They have carbon fibers in their bone structure. I have yet to see someone with natural carbon fibers in bones on Earth. That's definitely different.

 

[pseudophonist]

Not only that, the Na'avi also have only 4 limbs unlike the rest of (assumedly) vertebrate life on their planet, which have 6. So the Na'avi aren't just inconsistent with life as we know it, but also life as the rest of Pandora knows it.

 

[DaveC426913]

You have been not paying attention. They have carbon fibers in their bone structure. I have yet to see someone with natural carbon fibers in bones on Earth. That's definitely different.

Not only that, the Na'avi also have only 4 limbs unlike the rest of (assumedly) vertebrate life on their planet, which have 6. So the Na'avi aren't just inconsistent with life as we know it, but also life as the rest of Pandora knows it.

These are utterly superficial details when considering "life as we know it".

What we were supposing was a form of macrolife that could somehow flourish under a sun that's a half billion miles away. That is 1/25th the amount of light that Earth receives.

At the very least, Pandora would be in eternal late twilight. You will not get leaved plants, and you sure won't get trees. Why would any form of vegetation spend any energy climbing to the sky?

Yet Pandora has liquid water. Tidal activity is the next most likely candidate for energetic influx. In all likelihood, the life-giving energy is from underneath, not above.

Life on such a planet would not, could not look or metabolize anything like macrolife as we know it.

And finally, since Pandora does contain macrolife very similar to Earth life, we know it is has similar solar influx, and therefore, a gas giant could not be made of methane and be so close to its primary.

 

[QuantumPion]

Maybe Pandora and its parent ice giant are in a double or multi-star system. They could have some sort of non-regular / long period orbit which allows both to exist.

 

[DaveC426913]

Maybe Pandora and its parent ice giant are in a double or multi-star system. They could have some sort of non-regular / long period orbit which allows both to exist.

But at the same time in the same place?

 

[QuantumPion]

But at the same time in the same place?

Maybe the ice giant formed when the planetary system was at a long distance from a star, but due to orbital perturbations got pushed into a orbit in the habital zone which caused its moons to become earth-like. Who knows, I'm just speculating :)

 

[DaveC426913]

Maybe the ice giant formed when the planetary system was at a long distance from a star, but due to orbital perturbations got pushed into a orbit in the habital zone which caused its moons to become earth-like.

I suppose, if it managed to get perturbed and virtually rocket into the inner solar system fast enough that the methane and ammonia didn't burn off, (which would happen in the blink of an eye compared to orbital migration).

One would then have to wonder why the planet isn't still wobbling from its meteoric trip followed by its stand-itself-on-its-bumper stop.

Who knows, I'm just speculating :)

Indeed.

 

[MotoH]

Clearly the picture was taken with a #38a dark blue filter to reduce the glare and enhance cloud bands.

 

[DaveC426913]

Clearly the picture was taken with a #38a dark blue filter

Alas, a yellow-red planet through a blue filter will appear virtually black. Good one though...