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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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  • And Hot Jupiters? (Score:3, Interesting)

    by Geoffrey.landis (926948) on Friday January 23, 2009 @11:32AM (#26575765) Homepage
    Hmm-- the new model doesn't seem to account for the fact that planets don't stay in the place where they're formed; gravitational interactions can slingshot them around the early solar system. There's really no other way to account for "hot jupiters," gas giants that are very close to the star.
    • Re:And Hot Jupiters? (Score:4, Interesting)

      by clonan (64380) on Friday January 23, 2009 @11:51AM (#26576143)

      Very true but the 4 inner planets have almost circular orbits.

      Any planet that get flung around will have a very eliptical orbit.

      The Hot Jupiters are a different thing. They are caused by the system having enough material to cause drag and slow them down enough to collapse the orbit.

      • Re:And Hot Jupiters? (Score:5, Interesting)

        by Geoffrey.landis (926948) on Friday January 23, 2009 @12:37PM (#26577073) Homepage

        Very true but the 4 inner planets have almost circular orbits.

        Any planet that get flung around will have a very eliptical orbit.

        Orbits get circularized by a number of effects over time, both orbital and viscoelastic coupling. Hot-Jupiter orbits somehow get circularized, after all, and they're much harder to circularize than smaller planet orbits.

        The Hot Jupiters are a different thing. They are caused by the system having enough material to cause drag and slow them down enough to collapse the orbit.

        Any process that can move Jupiter and super-Jupiter size planets will easily reposition smaller planets.

        • Re: (Score:2, Interesting)

          by jameskojiro (705701)

          How do we know that our system didn't have a Super Jupiter that was gobbled up by the sun sometime in the solar system's past.

          A super Jupiter being gobbled up by our sun could have caused a mass extinction in earth's past.

          It would probvably cause a lot of radiation to be released by the sun and some quite large coronal mass ejections.

          Just because we don't have one now doesn't mean we didn't used to have one.

        • by clonan (64380)

          Anything that moves a super-sized planet will eject smaller planets from the system.

          The hot-jupiter orbits start circular and are slowly spiralled in.

          Actually, most eccentric orbits will be maintained. Only specific conditions will circularize an orbit and most eccentric orbits that get curcularized become unstable in the process.

          It is very unlikely that the inner planets moved much with the possible exception of mercury.

          • Anything that moves a super-sized planet will eject smaller planets from the system.

            Experimental evidence strongly suggests that there are no hot Jupiters in the solar system. Therefore, motion of hot Jupiters did not in fact scatter inner planets out of the solar system because our solar system does not have any hot Jupiters.

            However, the process by which hot Jupiters are repositioned also can reposition smaller planets. There's nothing special about Jovians that allows them to move but forbids smaller planets to move. The observation of hot Jupiters is a evidence of a mechanism that m

            • Re:And Hot Jupiters? (Score:5, Interesting)

              by clonan (64380) on Friday January 23, 2009 @02:11PM (#26578845)

              Eccentric orbit's are destabalized during the process of circularization which then either ejects them OR crashes the orbit. But it is also true the eccentric orbits tend to be a bit more stable than true circular ones...but only a little.

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

              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

              • by Geoffrey.landis (926948) on Friday January 23, 2009 @03:49PM (#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.

      • by w0mprat (1317953)
        The moon has a pretty circular orbit. The theory that the moon formed from a collision with earth is the leading theory since it's composition bares out this claim. I would assume the same effects that circularized it's orbit do apply to planets.
        • by clonan (64380)

          the moon formed extremly close to it's primary and that regularized it's orbit. In addition it formed out of an accretion disk created by the impact. These discs spontaeously circularize due to internal collisions.

          A better example are the moons of mars. They were both captured and both have a moderatly elliptical orbit.

          Your argument is exactly the same argument I am making. Planets that form out of an accretion disc will have regular orbits. Planets that are moved to there current position will tend to

  • by erroneus (253617) on Friday January 23, 2009 @11:34AM (#26575799) Homepage

    Venus and Earth are not even married! And now they are trying to say that Mars and Mercury are illegitimate children of a lesbian union of planets?!

    NO! I will not accept it! GOD DID IT! Things are the way they are because God did it that way and need no further explanation!

    • by kandela (835710)
      Well this hypothesis is even more heretical than you imagine. Think about it. We all know Men are from Mars and Women are from Venus. But the Bible says that Eve came after Adam. This theory flies in the face of that. If Mars was made after Venus then the Women must have been made first! Further, Men must have been made from the scraps of Women; rather than Eve being made from Adam's rib.
  • by faloi (738831) on Friday January 23, 2009 @11:35AM (#26575807)
    Sometimes when a mommy planet and a daddy planet love each other very much...
  • by CheshireCatCO (185193) on Friday January 23, 2009 @11:38AM (#26575869) Homepage

    If the rocky planets formed from a homogenous debris disk, they should all be roughly the same size and orbit the sun in similar circular orbits, Youdin explained.

    Uh, why? The disk varies with distance in the standard model. (Orbital speeds, density, composition, etc.) So you wouldn't even really expected the planets to have the same size.

    Armitage agreed. "In the standard model the composition varies with distance from the sun," he said.

    Huh, that's odd. There was work done about a decade or so ago that said the opposite: there was enough mixing between planetismals in the inner solar system to largely homogenize the compositions. But, then, Phil is an expert in this, so maybe more recent simulations have quashed that.

    • by CheshireCatCO (185193) on Friday January 23, 2009 @11:41AM (#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: (Score:3, Informative)

        by Bemopolis (698691)
        Banding is a natural consequence of planet formation. The comparatively stronger gravity of a protoplanet attracts nearby material, which accretes onto the protoplanet and makes it larger; or it changes the orbital energy of nearby material, driving it into a smaller orbit if the material is interior to the protoplanet's orbit, or into a larger one if it is exterior to the p-planet.

        The comparison to the rings of Saturn is useful, but not completely germane. The banding of Saturn's rings is more akin to
  • I always thought that the Martians were the rejects and outcasts anyway. But what about those Venusians? Haven't heard or seen much of those legendary critters.
  • under the chocolate outer crust lies a whipped center, and caramel.
    • by kandela (835710)
      Instead of looking for water at the poles we should be looking for a Coke instead.
  • You know what? (Score:1, Flamebait)

    by HaeMaker (221642)

    All of the planets formed in the general vicinity of the sun from the same materials. OF COURSE, their cores should have a similar makeup, THEY ALL SHOULD! This does not prove anything.

    These stupid astronomers need to get a real job.

    • Why would they be the same material? Why is the disk homogenous? The temperature gradient and dynamical gradients could, in fact, cause the disk to differentiate.

      • by Locke2005 (849178)
        I was going to say the temperature gradient wouldn't make a difference, but it would if it was enough to cause a phase-change in the material. Gases would be more likely to be blown outward by the solar wind. The disk would be non-homogenous because there is a sun in the middle of it, not a point source of gravitational force!
        • Re: (Score:3, Interesting)

          by CheshireCatCO (185193)

          Sort of. The real effect is in what is solid enough to accrete. Gases don't participate, which is why you find so little hydrogen compounds (water, methane, ammonia) in the inner solar system relative to what you would normally expect and why the giant planets are, well, giants.

          I don't believe as it's currently thought that the proto-Sun had a wind during the planet formation stages. If there were, it'd surely hamper the process. (Eventually, it would have done so when it cleared out the system.)

  • ...that's a big Venus!
  • New book title coming soon: Mars is from Earth, Mercury is from Venus.

  • The earth and venus were fucking and made the stupid war and speedy communications and shit what do we DO!

    "No worries I have my SUPERNOVA OF NATURAL SELECTION"!!!!

  • created by a racnoss spaceship attracting other stuff to it? The Doctor said so! http://tardis.wikia.com/wiki/The_Runaway_Bride [wikia.com]

The use of anthropomorphic terminology when dealing with computing systems is a symptom of professional immaturity. -- Edsger Dijkstra

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