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Space Science

Mars, Mercury May Have Formed From Earth and Venus 73

Posted by kdawson
from the brothers-under-the-skin dept.
goran72 sends along a report on a radical new theory of planet formation that suggests that Mars and Mercury were formed from the scraps of Earth and Venus. The theory has testable predictions — for example that the compositions of the rocky inner planets should be more similar than the current theory of planet formation would have them.
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Mars, Mercury May Have Formed From Earth and Venus

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  • by CheshireCatCO (185193) on Friday January 23, 2009 @12:41PM (#26575923) Homepage

    Also, I wonder how they get the protoplanetary disk to break up into bands. Saturn's rings aren't really banded as much as you might think. The degree to which they are is largely due to moons (or their on-going generation). Left to themselves, the rings should spread and homogenize.

  • Re:Falsifiability (Score:5, Insightful)

    by QuoteMstr (55051) <dan.colascione@gmail.com> on Friday January 23, 2009 @02:23PM (#26577981)

    The Structure of Scientific Revolutions [barnesandnoble.com], Thomas Kuhn's magnum opus, should be required reading before engaging in a debate on science. There's an aphorism that goes "all theories are wrong, but some are useful." We can and do use theories we know have flaws because in the vast majority of cases, they predict and explain what happens in nature. When a better theory comes along to explain the observations, we begin to use that one instead.

    It's absolutely useless to say "this theory is wrong!" as long as the theory, however flawed in some cases, works well in the general case. What do you propose to replace it? Does your replacement make specific, verifiable assertions about nature that are more correct or accurate than those of the prevailing theory? I thought not.

    (On the off chance that it does, and you can provide evidence, please, submit an article to Science or Nature; you'll be famous for generations.)

  • Re:Falsifiability (Score:4, Insightful)

    by Hatta (162192) on Friday January 23, 2009 @02:24PM (#26577997) Journal

    The more petty among you will read what I said and decide (entirely without consulting me) what alternative theory I believe in and will probably proceed to make a contest of it because you cannot grasp the simple essence of "this is an open question" and therefore cannot conceive of anything except one ideology versus another. It's alright not to know; sometimes there is great freedom in it.

    The problem with just "not knowing" is what do you do then? I agree we shouldn't treat these theories as absolute truth, but that doesn't mean they're not useful. The scientific method works by making a hypothesis, making predictions from that hypothesis, testing them, and modifying the hypothesis if necessary. But you have to start somewhere. Make some guesses, even if they're bad guesses. If you just shrug your shoulders and say "I dunno", you'll never get anywhere.

  • Re:Falsifiability (Score:5, Insightful)

    by TheTurtlesMoves (1442727) on Friday January 23, 2009 @02:49PM (#26578457)
    Nice rant. Got anything to back it up? I mean other than they are all wrong.

    Your comment on frozen lines in plasma not withstanding. Its an approximation, that works well for a lot of cases. And anyone in the field will tell you that. Newer models allow this to be relaxed more and more. But really it doesn't change things that much with typical astronomical plasmas.

    And the different redshift thing? Could you be more specific? There are really no theories that predict the comsmic microwave background and isotope ratios other than the big bang. Which also leads to the standard red shift interpretation. There really nothing else we have come up with that works. We have just have so much red shift data now. There really are no alternative that explain this without some serious arm waving.

    and are humble enough to admit that maybe you don't know

    I'm sure you are humble enough for both of us.

  • Re:Falsifiability (Score:4, Insightful)

    by DaveV1.0 (203135) on Friday January 23, 2009 @03:06PM (#26578731) Journal

    The more petty among you will read what I said and decide (entirely without consulting me) what alternative theory I believe in

    Then, perhaps you should elaborate in what alternative you believe in instead of making pronouncements about how wrong a theory is without offering a more valid alternative.

  • by Geoffrey.landis (926948) on Friday January 23, 2009 @04:49PM (#26580495) Homepage

    Eccentric orbit's are destabalized during the process of circularization which then either ejects them OR crashes the orbit.

    I can't make any sense out of this statement. "Circularization" is by definition decreasing the eccentricity of an orbit. Decreasing the eccentricity of an orbit will not "eject" or "crash" the orbit; you have to increase the orbital eccentricity to do that. You can't "destabilize" an orbit by "circularizing" it; the two things are opposites.

    But it is also true the eccentric orbits tend to be a bit more stable than true circular ones...but only a little.

    I have not the slightest notion what you mean here. Circular orbits are not unstable! About the most you can stay is that circular orbits are "destabilized" into elliptical ones, but I can't see how that makes them "less stable" that orbits that start out elliptical in the first place.

    I never said the sol system had a hot jupiter. But it had been cited in the grandparent therefore I was adressing the issue. Hot Jupiters happen in specific conditions where the gas that formed the original system was thick enough to not get blown away quickly. Therefore the jupiter sized planet, with it greater porportional size and gravitational field effect due to lower density, are disporportinaly slowed through friction.

    I don't know what model you're assuming, and I don't know what you mean by "disproportionately" or what sort of scaling law you're assuming. About the best I can say here is that it is extremely model dependent.

    As they slow they eat or eject all inner planets until they get close enough so that the solar wind HAS cleared everything out.
    The sol system did not have these conditions therefore no hot Jupiter.
    With the higher density but smaller size of rocky planets they are not as likley to experience the slowing effect before they clear the neighboring space

    about all I can say is that this is extremely model dependent. If the small rocky planets are clearing their region, as you note, the amount by which they move in reaction is going to be inversely proportional to the planet's mass, and hence smaller planets will move more, not less. Have you actually calculated a scaling law? It will depend on what you assume to be the dominant effect, but it's not at all clear that the mechanism vanishes with small planets.

    therefore any moving will probably be due to colision or near collision with other large bodies and will be entierly random.

    Random, yes.

    The reason Venus, Earth and Mars probably haven't moved is because the planets chemistries match theory fairly closely. Planetary genesis theories suggest that there will be subtly chemical differences at varius altitudes from the star. Mercury has unexpected chemistry which could come from collision (there is evidence for such an event) or being moved

    There is not enough chemical knowledge of the composition of the inner planets to definitively base this statement on experimental data. (Venus in particular is very poorly characterized). The chemistry seen on the surface is highly affected by the planetary differentiation (that is, what got segregated to the core), and we currently know little about the cores of Mars, Venus, or Mercury.

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