I'm sorry if this shouldn't be posted here, this being a discussion of Earth Science, but even though there's some biology and chemistry mixed in, I think it's pretty on-topic. Feel free to delete/move it if it isn't. I'm starting to plan for writing a book, so naturally I have to have everything pretty realistic... Kinda fantasy, as many of the races would never exist on our planet, mostly because of the lack of a great amount of carbon/CO2 in the atmosphere, the warmer and younger planet, and the "jumpstarted" evolutionary cycle (there was less CO2 in the air when the world was first being made, and the first extremeophile prokaryotes [simple, single-celled organisms with no nucleus that reproduce asexually], who relied more on the stronger sunlight and therefore more heavily on radiation, meaning that they went through more photosenthesis ie, more oxygen, blah, blah, blah...), but that's a little OT... I'm currently trying to draw in the tectonic plates, and being a perfectionist who naturally isn't perfect, I've been having little success. I understand that the plates move because of conduction currents within the earth, specifically within the semi-solid mantle, but... this is a different world, and I have little idea how the larger size and different proportions would work out. With our world (roughly, of course, as all measurements are disputed and argued against by SOMEONE), the crust is 30 km thick, the upper mantle (lithosphere) 720 km thick, the lower mantle (asthenosphere) 2171 km thick, the outer core 2259 km thick, and the inner core 1221 km thick. In my world, hypothetically, it would be crust - 150, lithosphere - 1620, asthenosphere - 3060, outer core - 3210, and inner core 1500. However, these measurements are partially hypothetical as I still have not worked out whether gravity and the density/weight of all of that material and it's effects on what's below it. The more gravity, the more it's being pulled on, and to negate that effect there would have to be another force of gravity acting upon the same material, which, again, I still have not fully worked out. I have decided that it will be a solar system with two stars, meaning that there will be a period of time each year where there is no night. I've already taken that into effect, and I think that it would be a time of many earthquakes and stretching and a lot of changing of the tectonic plates as the dual forces of gravity act upon the same thing, but I'm not sure if that would have the exact desired effect. Although, because the suns are different masses and lengths away from the planet, I think that it would stay in orbit around the larger one, since it not only has more mass, ie more gravity, but it's closer to the center of gravity that the suns share. (This was the one problem I had with the movie Pitch Black - it showed one sun orbiting around another - which is, I believe, completely impossible. There would be a center of gravity that they share. The smaller sun would be farther away, and the larger one closer. It's an equilibrium equation wherein mass * distance = mass * distance. Very simple, learned probably in the sixth or seventh grade...) I was wondering if anyone had any ideas on the effects of the material of the asthenosphere, how it would act with the greater force of gravity and greater weight that's on it, and how that would effect plate tectonics would help. Any criticisms of what I've already got would be greatly appreciated. If anyone wants any more information on this please feel free to PM me or post here. I'd love to hear anything you've got to say...
I am afraid that the double sun scenario is unlikely to work; if the planet is in a stable orbit around one star, the other one is likely to be so distant that it will be very small in the sky, barely showing a disk even at closest approach; Alpha Centauri is a good example of this. There would not be a bright sun in the night sky, rather a brillliant point of light. Perhaps if the more distant star of the pair has entered a red giant phase it will be both brighter and larger in the sky. However the expansion of a sun-mass star into a red giant is accompanied by a helium flash, which would be injurious to the biosphere of a lifebearing world; generally red giants are not healthy things to hang around for too long. As far as tectonics goes, I don't really know; but let's speculate. Many Earth-sized planets are likely to have crusts with different thickness to that of the Earth, and a different overall density. This is because the exact conditions of the creation of the Moon from an impact with a large planetoid are not likely to be replicated in other solar systems. It is very possible that our Moon could have been formed as a smaller, or a larger, body, or that no collision occured at all; in which case the tectonic plates might have been thicker, or thinner, or non existant. The gravity of a distant companion star is unlikely to have much effect on the crust of a planet; if the star is close enough to be very brilliant in the night sky and show a noticeable disk it would disrupt the orbit of the planet and the planet wouldn't be there.
Not addressing your specific questions, but one of the reasons plate tectonics seems to work on the Earth is that we have mainly oceanic crust, that is a lot thinner than the continental crust. If it was continental crust the whole way around any proto-plates would lock up - end of plate tectonics. We likely have so little continental material because of the collision from which the moon was formed. So without a (probably) very rare chance of a Mars sized world hitting to remove the early crust (and much of the upper mantle), no plate tectonics. You haven't said anything about the hydrosphere. You need one. Without water to act as a lubricant, again the plates probably lock up. I'm pretty certain, as eburacum has said that you are going to find it well nigh impossible to obtain an orbit that is stable in the long term in a binary system. You seem to be hoping that the effects of the two stars will trigger plate activity. This is unlikely. The moon exerts twice the gravitational influence on the Earth as does the sun because it is so close, yet we don't have any significant correlation between the moon's phases and earthquake activity. Shoot. I didn;t mean to sound so negative, but I think these are all points you would have to work around somehow. Good luck with the writing.
Thanks so much all of you. Geez, I feel dumb. Heh, there's only so far that science teacher's'll get you. Yes, the world does have a hydrosphere, and quite a bit of water, I think it's somewhere between 70 and 76 percent of the surface area. With the drops in the level of the oceanic crust, that's quite a bit... Thanks for your recommendations with the crust and the dual forces of gravity. I seem to reach a point when my own thinking starts to go in circles. I think that with what you've all said, which makes perfect sense to me, I should hope/think more about the asthenosphere and less of gravity to effect plate movement... Which could be justified by it being hotter, ergo faster, but I have to take into effect that it's got more space to flow within and the fact that it's a bigger planet, ie, more gravity, and there's more on top of it slowing it down. I think it would probably be just a little over the movement of our plates. However... I think a geologist would be better at this than me... Hmmm... Geology website... *goes off to look for a geology q&a department with little hope of finding one*
How about the gravity on that planet? Would be a tad more complicated. Will the compression effect increase the density. I would expect a higher gravity than simply taking earth specific mass with a bigger volume.
Yeah, that directly effects erosion. Heavier rains. Smoother surface. There's only one really big mountain on the planet, and it's a volcano, and it'll eventually be gone, too, because of the increased erosion. Wow, my planet seems to do ALOT faster than other planets... rain... biological processes that started life... Ah, speculation... Please Register or Log in to view the hidden image! I love it and I hate it... just like everything else...
