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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 @12:32PM (#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.
  • by CheshireCatCO (185193) on Friday January 23, 2009 @12:38PM (#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.

  • Re:And Hot Jupiters? (Score:4, Interesting)

    by clonan (64380) on Friday January 23, 2009 @12:51PM (#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 @01:37PM (#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:And Hot Jupiters? (Score:2, Interesting)

    by jameskojiro (705701) on Friday January 23, 2009 @02:31PM (#26578117) Journal

    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 CheshireCatCO (185193) on Friday January 23, 2009 @02:47PM (#26578437) Homepage

    Actually, it's the reverse. If you put a planet in the disk, it tries to open a gap. (See the Keeler and Encke gaps in Saturn's A ring for examples.)

    So that's not it. (And besides, it sounds like these guys are positing the bands form FIRST.)

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

    by clonan (64380) on Friday January 23, 2009 @03:11PM (#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

  • Re:You know what? (Score:3, Interesting)

    by CheshireCatCO (185193) on Friday January 23, 2009 @05:24PM (#26581103) Homepage

    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.)

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