The Origin of the Solar System - The Diigo Meta page

• 21 Apr 08
  

  James Linzel

  # A cloud of interstellar gas and/or dust (the "solar nebula") is disturbed and collapses under its own gravity. The disturbance could be, for example, the shock wave from a nearby supernova.
  
  # As the cloud collapses, it heats up and compresses in the center. It heats enough for the dust to vaporize. The initial collapse is supposed to take less than 100,000 years.
  
  # The center compresses enough to become a protostar and the rest of the gas orbits/flows around it. Most of that gas flows inward and adds to the mass of the forming star, but the gas is rotating. The centrifugal force from that prevents some of the gas from reaching the forming star. Instead, it forms an "accretion disk" around the star. The disk radiates away its energy and cools off.
  
  # First brake point. Depending on the details, the gas orbiting star/protostar may be unstable and start to compress under its own gravity. That produces a double star. If it doesn't ...
  
  # The gas cools off enough for the metal, rock and (far enough from the forming star) ice to condense out into tiny particles. (i.e. some of the gas turns back into dust). The metals condense almost as soon as the accretion disk forms (4.55-4.56 billion years ago according to isotope measurements of certain meteors); the rock condenses a bit later (between 4.4 and 4.55 billion years ago).
  
  # The dust particles collide with each other and form into larger particles. This goes on until the particles get to the size of boulders or small asteroids.
  
  # Run away growth. Once the larger of these particles get big enough to have a nontrivial gravity, their growth accelerates. Their gravity (even if it's very small) gives them an edge over smaller particles; it pulls in more, smaller particles, and very quickly, the large objects have accumulated all of the solid matter close to their own orbit. How big they get depends on their distance from the star and the density and composition of the protoplanetary nebula. In the solar system, the theories say that this is large asteroid to lunar size

  solarsystem planets

  • • A cloud of interstellar gas and/or dust (the "solar nebula")  is disturbed and collapses under its own gravity. The disturbance  could be, for example, the shock wave from a nearby supernova.  

       

    • As the cloud collapses, it heats up and compresses  in the center. It heats enough for the dust to  vaporize. The initial collapse is supposed to take  less than 100,000 years.  

       

    • The center compresses enough to become a protostar  and the rest of the gas orbits/flows around it. Most  of that gas flows inward and adds to the mass of the  forming star, but the gas is rotating. The centrifugal  force from that prevents some of the gas from reaching  the forming star. Instead, it forms an "accretion disk"  around the star. The disk radiates away its energy and  cools off.
  • • The gas cools off enough for the metal, rock and (far  enough from the forming star) ice to condense out into  tiny particles. (i.e. some of the gas turns back into dust).  The metals condense almost as soon as the accretion disk  forms (4.55-4.56 billion years ago according to isotope  measurements of certain meteors);  the rock condenses a bit later (between  4.4 and 4.55 billion years ago).  

       

    • The dust particles collide with each other  and form into larger particles. This goes on  until the particles get to the size of boulders  or small asteroids.  

       

    • Run away growth. Once the larger of these  particles get big enough to have a nontrivial  gravity, their growth accelerates. Their gravity  (even if it's very small) gives them an edge over  smaller particles; it pulls in more, smaller particles,  and very quickly, the large objects have accumulated  all of the solid matter close to their own orbit.  How big they get depends on their distance from  the star and the density and composition of the  protoplanetary nebula. In the solar system, the  theories say that this is large asteroid to lunar  size in the inner solar system, and one to fifteen  times the Earth's size  in the outer solar system. There  would have been a big jump in size somewhere  between the current orbits of  Mars and Jupiter:  the energy from the Sun would have kept  ice a vapor at closer distances, so the solid,  accretable matter would become much more common  beyond a critical distance from the Sun. The  accretion of these "planetesimals" is believed  to take a few hundred thousand to about twenty  million years, with the outermost taking the longest  to form.
  • • At this point, the solar system is composed  only of solid, protoplanetary bodies and gas  giants. The "planetesimals" would slowly collide  with each other and become more massive.  

       

    • Eventually, after ten to a hundred million years,  you end up with ten or so planets, in stable orbits,  and that's a solar system. These planets and their surfaces  may be heavily modified by the last, big  collision they experience (e.g. the largely  metal composition of Mercury or the  Moon).

  1 more annotation...

• 07 Oct 05
  

  Jeff Stanger

  Astronomy

Would you like to comment?

Join Diigo for a free account, or sign in if you are already a member.