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Earth Space News

How Earth Avoided a Fiery Premature Death 114

Posted by kdawson from the flood-next-time dept.
Hugh Pickens writes "Space.com has a piece about changing theories of planet migration. The classic picture suggests that planets like Earth should have plummeted into the sun while they were still planetesimals, asteroid-sized building blocks that eventually collide to form full-fledged planets. 'Well, this contradicts basic observational evidence, like We. Are. Here,' says astronomer Moredecai-Mark Mac Low. Researchers investigating this discrepancy came up with a new model that explains how planets can migrate as they're forming and still avoid a fiery premature death. One problem with the classic view of planet formation and migration is that it assumes that the temperature of the protoplanetary disk around a star is constant across its whole span. It turns out that portions of the disk are opaque and so cannot cool quickly by radiating heat out to space. So in the new model, temperature differences in the space around the sun, 4.6 billion years ago, caused Earth to migrate outward as much as gravity was trying to pull it inward, and so the fledgling world found equilibrium in its current, habitable, orbit. 'We are trying to understand how planets interact with the gas disks from which they form as the disk evolves over its lifetime,' adds Mac Low. 'We show that the planetoids from which the Earth formed can survive their immersion in the gas disk without falling into the Sun.'"
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How Earth Avoided a Fiery Premature Death More

How Earth Avoided a Fiery Premature Death

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  • Neptune - Uranus shuffle (Score:5, Interesting)

    by sznupi ( 719324 ) on Sunday January 10, 2010 @09:16PM (#30718938) Homepage

    For me the most amazing aspect of planetary migration is the probable exchange of order for Neptune and Uranus, with Neptune being thrown out to the position of outer planet; without it being ejected from the system, plunging into the Sun or colliding with other big body. Though who knows, perhaps some planet was doomed that way; certainly wild axial tilt of Uranus isn't a testament of calm times.

    http://en.wikipedia.org/wiki/Nice_model [wikipedia.org]

    PS. There's some joke here, with Uranus ending up closer to the Sun, about total asses always ending the race in better place...

    • Re: (Score:1)

      by toastar ( 573882 )

      ok neat, But how did the main asteroid belt form again,

      • Re: (Score:3, Informative)

        by Nefarious Wheel ( 628136 )

        ok neat, But how did the main asteroid belt form again,

        Roche Limit [wikipedia.org] fail? Jupiter was nearby, relatively speaking, could have been a disruptive influence.

        • Re: (Score:2)

          by sznupi ( 719324 )

          Gravitational influence of Jupiter; Roche limit - NO!!! That's a very specific term, dealing with tidal forces when bodies get very near. In case of Jupiter & asteroid belt it was more about orbital resonances & energy transfer.

      • Re: (Score:2, Funny)

        by Anonymous Coward

        ok neat, But how did the main asteroid belt form again,

        According to Heinlein, the inhabitants of the original 5th planet annoyed the Martians.

    • Re: (Score:2)

      by mcgrew ( 92797 ) *

      Though who knows, perhaps some planet was doomed that way

      One was -- Earth. They think the moon formed when a Mars-sized object collided with Earth, and the molten rock that splashed condensed and coalesced into what is now our moon.

      What I wonder is how the collision affected its orbit?

      • Re: (Score:3, Informative)

        by sznupi ( 719324 )

        Not exactly. The body that caused formation of the Moon likely formed in Earth L4 or L5 point; technically making it not a planet. Coming from there also gives less chance for axial tilt such wild as in the case of Uranus...

        Since it was already gravitationally bound with Earth, I don't think it changed its orbit in significant way.

  • Soft on outside Crunchy on inside (Score:5, Interesting)

    by icebike ( 68054 ) on Sunday January 10, 2010 @09:40PM (#30719060)

    This would seem to suggest the inner planets formed first and swept the disk of hard derbies, leaving nothing but the gas, which was ultimately blown outward by the pressure of the sun as the disk was swept clear of big chunks.

    The gas giants would accumulate at a much slower rate, and almost by definition must be far younger than the rocky planets.

    Then there are the oddball moons of the outer planets. Captured planetoids forming late, almost falling into the sun because the disk was pretty much cleared by that time, but being slung outward and captured by chance?

    • Re: (Score:2, Funny)

      by Anonymous Coward

      This would seem to suggest the inner planets formed first and swept the disk of hard derbies...

      Then the disk sang to the Sun: "I'd tip my hat to you, but I haven't got a hat".

    • > This would seem to suggest the inner planets formed first and swept the disk
      > of hard *derbies*...

      So the Earth's crust is old hat?

    • NICE topic this is and i like this , and he work really hard, about this, Paraslime Force [ezinearticles.com]

  • Who knows (Score:2, Insightful)

    by BhaKi ( 1316335 )
    Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable.

    • Re: (Score:3, Informative)

      by Sulphur ( 1548251 )

      Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable.

      Al is that you?

    • Re: (Score:3, Insightful)

      by gyrogeerloose ( 849181 )

      Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable.

      Except for the fact that if something is falling slowly, it ain't a plummet. From the Oxford American Dictionary:

      plummet [verb]

      1 fall or drop straight down at high speed
      2 decrease rapidly in value or amount

      [noun]

      1 a steep and rapid fall or drop.

      • Re: (Score:2)

        by BhaKi ( 1316335 )

        I admit I didn't know the exact meaning of plummet when I posted it. Thanks for the info.

        Now there's another interesting idea. It's possible that the fall is quick in comparison to the sun's or earth's age, while still being many orders of magnitude longer than human lifetime.

    • "Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable."

      Well, we ARE plummeting into Sun at a very observable rate. It's only that such rate is exactly the same we move to the side to avoid the mark.

  • How did we avoid firey, premature death? (Score:5, Funny)

    by darkpixel2k ( 623900 ) on Sunday January 10, 2010 @10:10PM (#30719184)

    How Earth Avoided a Fiery Premature Death

    The dinosaurs were smart (especially the Velociraptors). They stopped driving SUVs. That's why we're here.

  • The article isn't great for the lay-person (Score:5, Interesting)

    by Cedric Tsui ( 890887 ) on Sunday January 10, 2010 @10:31PM (#30719286)
    If I'm reading the article right, it says that the gravity of a gas/rock disk around a star will cause the whole thing to migrate inward until it is consumed by the sun. However, account for temperature differences due to varying cooling rates across the disk, then this causes a different force which can be shown to balance out the inward migration.

    My question is. Why does the gravitational effects of a gas disk around a star cause inward migration? The only thing I would expect to cause inward migration would be friction resulting in the loss of kinetic energy. I haven't the foggiest idea how a temperature gradient can cause matter to climb out of a gravity well. Maybe I should go looking for the original paper.

    • Re: (Score:3, Informative)

      by MosesJones ( 55544 )

      Why does the gravitational effects of a gas disk around a star cause inward migration?

      Throw a ball up... it comes down. This is gravity. The "base state" for gravity is everything sticking in the centre. Now when something has the right velocity this acceleration towards the centre just causes it to form an orbit around the body.

      However given that gasses expand to fill up available space its very hard to have a stable orbit of gas moving at a constant velocity and thus obtaining an orbit. Gasses just do

      • "Throw a ball up... it comes down. This is gravity. The "base state" for gravity is everything sticking in the centre."

        Nope. Your ball analogy doesn't work here. Things in orbit STAY in orbit unless they somehow lose all of their kinetic energy. A ball behaves differently because it NEVER gains enough energy for an orbit. The article says it is the interaction between the cloud and the proto-planet that causes the proto-planets to migrate towards the sun.

        "We show that the planetoids from which the Earth formed can survive their immersion in the gas disk without falling into the Sun."

        I can understand this part. But the article also says that a gas disk with varying temperatures would cause certain orbits to migrate outwards instead of inwards and THIS

        • Things in orbit STAY in orbit unless they somehow lose all of their kinetic energy.

          Nope, they have to have ENOUGH velocity (Kinetic energy is about the energy required to get it to a given speed) at the right angle in order to counteract the acceleration of the object towards the planet. If the velocity (a vector) isn't right then it will either move out of the orbit into a further orbit (or even escape) if it is too fast or it will fall towards the planet if too slow (as inner orbits require faster veloci

          • "Nope, they have to have ENOUGH velocity"
            Yes. That's why I said things in orbit (meaning they already have an appropriate amount of speed in the right vector) stay in orbit... I didn't say random objects in the solar system stay in orbit.

        • Re: (Score:2)

          by khallow ( 566160 )

          I can understand this part. But the article also says that a gas disk with varying temperatures would cause certain orbits to migrate outwards instead of inwards and THIS is why proto-planets can survive. But it doesn't say how a temperature gradient can cause migration.

          My guess is that there's some sort of considerable net light pressure away from the star. Not acting directly on the planet, but on the gas cloud. What's probably different is that in old models, the light pressure acted only on the surface of the gas cloud, while in this model, due to the temperature gradient, you have light pressure much deeper in the cloud. This means the gas cloud is experiencing net force away from the star throughout a considerable portion of the cloud. That'll help keep planetoids fr

        • But the article also says that a gas disk with varying temperatures would cause certain orbits to migrate outwards instead of inwards and THIS is why proto-planets can survive. But it doesn't say how a temperature gradient can cause migration.

          I didn't read the whole article - far too mathematically dense - but I did get this understanding of the matter:
          Planetesimals orbit under essentially the rules of Kepler ; this establishes a baseline of velocities for comparison.
          A gas disk with a uniform temperature wi

    • I haven't the foggiest idea how a temperature gradient can cause matter to climb out of a gravity well.

      Thermophoresis [wikipedia.org] causes particles in a fluid to move because of a temperature gradient. The similarity parameters (Reynolds / Mach / Knudsen) for a planetesimal in an accretion disk are probably similar to the aerosal particles in air that the wiki article talks about.

  • Worst. Semantic. Structure. Ever. (Score:2, Insightful)

    by Anonymous Coward

    The incorrect use of periods to indicate emphasis is not linguistic evolution. It is just semantic stupidity. I wish it didn't catch on.

    • Yet, it would appear to have caught on. As such... it's linguistic. evolution. As an adult native speaker of English, what I say that effectively communicates my intended point to my intended audience... is English, particularly so if I am emulated by others. One could even argue that I don't have to be a native speaker, though in this case, it is unlikely that emulation by large audiences would occur, limiting the evolution to a temporary mutation. Yes, I am a fan of descriptive grammars.

    • Isn't it meant to emulate the delivery of one W. Shatner esquire, who pronounces each word as if it's a separate sentence?

  • Here's some more info (Score:4, Informative)

    by Greg Hullender ( 621024 ) on Sunday January 10, 2010 @11:17PM (#30719498) Homepage Journal
    According to Science Daily [sciencedaily.com] this was the result of a computer simulation which was designed based on a paper, published last year http://arxiv.org/abs/0909.4552 [arxiv.org] . The simulation was "one-dimensional," which seems curious, and they could only afford to simulate 1,000 years out of the estimated 1,000,000 such a disk is expected to last.

    So look for more reports of this sort over the next few years. Still, it looks like a big jump forward for our early-solar-system models.

    --Greg

    • Re:Here's some more info (Score:5, Informative)

      by enilnomi ( 797821 ) on Sunday January 10, 2010 @11:25PM (#30719548)

      You misread. The relevant paragraph is, "We used a one-dimensional model for this project," says co-author Wladimir Lyra, a postdoctoral researcher in the Department of Astrophysics at the Museum. "Three dimensional models are so computationally expensive that we could only follow the evolution of disks for about 100 orbits -- about 1,000 years. We want to see what happens over the entire multimillion year lifetime of a disk."

      • You're right. Oops. That still leaves us wondering what a one-dimensional model of the solar system is like, though. Likewise, one could expect better results over time as people do work out how to do three-dimensional models for longer periods.

        Good catch. Thanks.

        --Greg

        • Re: (Score:1, Informative)

          by Anonymous Coward

          Presumably, you'd do your modeling as a slice through the disk. Basically, what you're interested in is the effects at different distances from the sun. Hopefully, you can ignore the part about distance above/below the ecliptic and the actual whizzing around the sun, and just focus on a single radial.

  • I probably am the only one who misread the title as "How to avoid a fiery premature death."

    • The question is, how many slahsdot readers would it take for the probability of you not being alone becoming non-negligent. Given that, and the rate at which we find new slashdot readers all the time. It only follows that one day someone just like you will be found. but they might have tentacles.

  • How do we know if the death of Earth is premature? We have absolutely no relative data to compare an M-class planet's typical life.

  • 0.3 billion years old (Score:3, Funny)

    by Hal_Porter ( 817932 ) on Monday January 11, 2010 @01:51AM (#30720234)

    > 4.6 billion years ago

    I like the way it's just a bit bigger than 2^32 to stop you using 32 bit variables for the year.

    • Re: (Score:1)

      by Strake ( 982081 )

      That's why the appearance of 64-bit processors took so long in this solar system - never before necessary!

  • Premature? More like "long overdue" amirite.

  • So in the new model, temperature differences in the space around the sun, 4.6 billion years ago, caused Earth to migrate outward as much as gravity was trying to pull it inward

    Or, perhaps, gravity could be a consequence of temperature differences [scientificblogging.com], so the "pull" and the "push" don't really happen.

  • "It turns out that portions of the disk are opaque " Maybe I'm off my rocker but the way this is stated, it sounds like a fact they observed rather than a model that they created. While this "fact" makes logical sense it is far too often that I see the statement "It turns out..."
  • And here I was all along believing it had something to do with Bruce Willis!
  • Astronomers have announced over 500 extra-solar planets and they have barely begun looking. So there are a lot of processes out there creating planets in spite of hypothetical process which may destroy them.

  • Any statistic significantly skewed by adding or subtracting 1 to either your numerator or denominator is a statistic too fragile to support a conclusion.

    The "we are here" argument is a functional celebration of innumeracy, which reminds me of Operation HUMBUG when Canada first introduced Metric: inference by nostalgia.

  • 'Well, this contradicts basic observational evidence, like We. Are. Here,' says astronomer Moredecai-Mark Mac Low.

    Well, this didn’t stop dark matter supporters, did it? ;)

  • There is no better way to sum up some of the gaps between theoretical and applied science other than: "This contradicts basic observational evidence, like We. Are. Here." Did the proponents of the "classic" model not notice this minor flaw in their reasoning?

    SirWired

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