How the 'verse works.

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Originally posted by jewelstaitefan:
I had read that it was projected that the sun wold continue growing and would swallow earth in some billions of years - perhaps that theory has been discounted.

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No, it hasn't been discounted. It's just the time dependence that I'm nitpicking about. The swallowing-the-earth thing isn't a gradual expansion of the sun, but a sudden change that will occur way way in the future.

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I wasn't clear. I meant the atmo mars got from the formative years of our galaxy - clearly mars formed after the sun. But I meant tha the conditions were different when mars first got it's atmo, and were sufficieently different after impact/collision that it had difficulty revcovering it's atmo.

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So... how could Mars have formed an atmosphere in the first place, if it can't recover one after a collision? (Yes, I'm nitpicking again...)

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I don't agree about summer/winter. Winter is when that portion of the globe is tilted away from the sun - not getting the rays PER DAY. the rays per area of the globe remain constant, holding the globe's overall temps consistent - or as consistent as the fluctuatuions of sun output allow.

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Length of day is certainly a factor, but the angle of the sunlight is a bigger one. To quote wikipedia (though lots of other web sites and textbooks would tell you the same):

"Seasonal change in the angle of sunlight, caused by the tilt of the earth's axis, is the basic mechanism that results in warmer weather in summer than in winter (see Figure 1). Change in day length is another factor."
http://en.wikipedia.org/wiki/Effect_of_sun_angle_on_climate

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Regarding proportion mentioned below, was recalling th4e galaxy incorrectly, and mercury to jupiter is too much of an extreme example.

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You're still confusing terminology here. The galaxy - the Milky Way - is the huge huge conglomerate of stars that the sun and all it's planets is a tiny part of. "Galaxy" and "solar system" are two completely different things.

As for Mercury and Jupiter being extreme examples - isn't that the point of this whole discussion? Seeing if a single planetary system could have so many terraform-able planets as the `verse requires?

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consider one or two beams of rays. the amount of energy the beam has at earth's orbit versus the amount of energy the same, uninterrupted beam would have at neptune's orbit shoud not be that different. I am talking about the energy of the beams, you are still talking about the amont of beams reaching the same square foot - which i addressd above, and was done with by this point. understand?

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I understand what you're saying, but you're inventing your own physics. Your basic assumptions are incorrect. This is the thing:



Sunlight is not a laser beam. Rays may appear to be parallel here on earth and we often use that assumption for applications on the scale of our planet. The distance involve - the top of our atmosphere down to the surface - is tiny compared to the sun/earth distance, so the divergence of the rays is negligible in our little world.

But when you're talking about the distance from earth to neptune, or even earth to mars, the rays are most certainly not parallel, and the beam of light diverges - geometrical spreading. This is a well understood and accepted phenomenon of physics.

You can insist on drawing a rectangular beam if you want, but it'll look like this:



The sunlight doesn't follow the white rectangle. The rays are denser - the light more intense - at the left end of the white box than the right end.

I like making pictures.

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Originally posted by jewelstaitefan:
I wasn't clear. I meant the atmo mars got from the formative years of our galaxy - clearly mars formed after the sun. But I meant tha the conditions were different when mars first got it's atmo, and were sufficieently different after impact/collision that it had difficulty revcovering it's atmo. Also, the collision would have been fatal for the asteriod as well, whcih mayu have originated from the asteriod belt, but would not have returned there. And the asteroid belt woold or could have already existed before the colliosion of mars. I'm thinking something like the yucatan impact - wiping out mars' atmo, not creating more asteroids or large rubble.

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I believe current theory is actually that because Mars hasn't a magnetosphere anything like Earths, the 'pressure' of the solar wind actually blew the Martian atmosphere away.

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consider one or two beams of rays. the amount of energy the beam has at earth's orbit versus the amount of energy the same, uninterrupted beam would have at neptune's orbit shoud not be that different. I am talking about the energy of the beams, you are still talking about the amont of beams reaching the same square foot - which i addressd above, and was done witth by this point. understand?

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I believe what you are trying to say is that a photon from the sun, will have the same energy at Earth as it will at Neptune. For simplicities sake, yes it will, but the energy of any single photon is entirely unimportant overall, its the number of of photons that's more important. The energy of received by the sun is subject to the inverse square law, that is if you double the distance the energy will drop to a quarter.

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... what they said.

Basically what ends up happening is that yes, Neptune gets sunlight, but as I mentioned before, the intensity of that light at noon there is the same as the intensity of light at a dim dusk here. Something else to consider, is the dispersion of the light, which is what Mal was trying to get at. It's very true that the rays travel outwards from the sun, but they do so in a wave instead of a beam, much like the light from the porch that I was trying to convey. Over space the light (and heat) gets dispersed and thus is weaker; you can still see it but it's the watered-down version.

That is also something that I didn't have time to mention that citizen did; the atmosphere of Mars was blown away by solar wind. The energy put out by the sun is more than light and heat, it's also electromagnetic energy, and a bit of kinetic energy. There is a vacuum in space, it's true, but the amount of energy produced by stars is enough to affect something as delicate as an atmo. When there are other factors aside from the solar wind affecting the atmo, such as a cooling core, planetary collisions, and a number of other things, yes, you could expect an atmosphere to blow away. Couldn't really pin it on one or the other of those things though.

^^

Are there any more points that I missed?


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Originally posted by meimeiCobb:
Basically what ends up happening is that yes, Neptune gets sunlight, but as I mentioned before, the intensity of that light at noon there is the same as the intensity of light at a dim dusk here.

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I think it's probably a fair bit less than a dim dusk .

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It's very true that the rays travel outwards from the sun, but they do so in a wave instead of a beam, much like the light from the porch that I was trying to convey.

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A small nit-pick, Light is always a wave, even if its a highly coherent laser beam. Well, actually just like everything else it's also a particle, Wave Particle Duality, confusing physicists since 1905.

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That is also something that I didn't have time to mention that citizen did; the atmosphere of Mars was blown away by solar wind. The energy put out by the sun is more than light and heat, it's also electromagnetic energy, and a bit of kinetic energy. There is a vacuum in space, it's true, but the amount of energy produced by stars is enough to affect something as delicate as an atmo.

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Actually there's much more to solar wind than em radiation. I'd also note that heat and light from the sun is electromagnetic radiation.

Space it self isn't a true vacuum, there's actually a lot of stuff out there, around Earth the density is roughly 5 particles per cubic centimetre, mostly charged plasma. It's this Plasma which is basically what we call the solar wind, and also causes the Aurora Borealis and Aurora Australis. These particles tend to whip along at a fair rate, both because they're shot out of the sun at high speed, and driven by the Sun's magnetic field (which is also strengthened by the solar medium, essentially the whole system acts like a giant Magneto-hydrodynamic generator).

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When there are other factors aside from the solar wind affecting the atmo, such as a cooling core, planetary collisions, and a number of other things, yes, you could expect an atmosphere to blow away. Couldn't really pin it on one or the other of those things though.

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I think we're looking at the process starting as the Martian core cooled. Current theory has it (and certainly seems to be supported by available evidence) that its a molten rotating Iron core that generates a planets magnetosphere, the invisible 'forcefield' that literally stops the solar wind impacting a planet. As the core cools, it stops spinning, it stops generating the planets magnetosphere, the solar wind can get at it. There's a lot of power in the solar wind, acting over a long time. I suspect that the solar wind alone could strip a planets atmosphere, no collisions required.

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Originally posted by mal4prez:
Meimei - have you heard of Lagrangian points? It's one way to get more bodies into a solar system. ( http://en.wikipedia.org/wiki/Lagrangian_point)

Oh, and which image do you mean? The one you included isn't working for me.

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I hadn't heard of that; thank you for that link, very informative.

And I fixed the link; you have to copy and paste it now.


http://www.leavemethewhite.com/
caps/albums/movies/serenity/
Serenity_0007.jpg
(COPY THE URL & PASTE IT INTO YOUR BROWSER)


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