• 04 May 08
  

  adebajo
• 25 Apr 08
  

  kevinlballa

  • protosun existed in a gaseous state.  As you move outward, the nebula is cooler.   At different radii, the  temperature is low enough for certain materials to condense.

     

     
• 24 Apr 08
  

  jrarzadon
• 21 Apr 08
  

  James Linzel

  solarsystem planets

  • Motion of the planets in their orbits:
  • 
  • asteroid belt
  • Kuiper  Belt

  • Large bodies in the solar  system have orderly motion. 

         

    All planets and most  satellites have nearly circular orbits, in the same direction, and nearly in  the same plane.  The Sun and most of  the planets rotate in the same directions as well.

           

    Planets fall into two main catelgories.

         

    Small, rocky terrestrial planets near the Sun and  large, hydrogen-rich jovian  planets farther out.  The jovian planets have many moons and rings made of rock and  ice.

           

    Swarms of asteroids and  comets populate the solar system.

         

    Asteroids are concentrated  in the asteroid belt, and comets populate the regions known as the Kuiper belt and the Oort cloud.

           

    There are several important  exceptions to these trends.

         

    Planets with unusual tilts,  very large moons, or moons with unusual orbits.

  • Large and diffuse, slowly rotating – it had some angular momentum.

      

    This property of the cloud primarily accounts for the motions of the planets. Why? Think about momentum and energy…

      

    <!--[if !supportLists]-->·      <!--[endif]-->Composed primarily of hydrogen and helium, but there must have been some heavier elements, including metals, since we find them in the terrestrial planets for example.

      

    This property of the cloud will dictate how the planets ended up in two main types.  Think about phases of matter…

  • The collapse is triggered by an increase in density, and driven by gravity.

      

     What do we mean by “collapse”? 

      

     

      

    During the collapse…

      

     

      

    <!--[if !supportLists]-->1.  <!--[endif]-->The cloud’s rotation rate increases, due to conservation of angular momentum.

      

     

      

    <!--[if !supportLists]-->2.  <!--[endif]-->The cloud heats up, as compressing the gas cause the particles to speed up, increasing the temperature of the gas and dust particles.

      

     

      

    <!--[if !supportLists]-->3.  <!--[endif]-->The disk of gas and dust flattens, as collisions between the particles of the cloud to lose energy in the direction perpendicular to the cloud’s rotation.

      

     

      

     

      

    <!--[if gte vml 1]><v:shape id="_x0000_s1026" type="#_x0000_t75"  href="solar_system_form.mov" style='position:absolute;margin-left:0;  margin-top:0;width:302.25pt;height:315.75pt;z-index:1;  mso-position-horizontal:left;mso-position-vertical:top;  mso-position-vertical-relative:line' o:allowoverlap="f" o:button="t">  <v:fill o:detectmouseclick="t"/>  <v:imagedata src="Formation%20of%20the%20Solar%20System_files/image002.emz"  o:title=""/>  <w:wrap type="square"/> </v:shape><![if gte mso 9]><o:OLEObject Type="Embed" ProgID="PlayerFrameClass"  ShapeID="_x0000_s1026" DrawAspect="Content" ObjectID="_1111394490"> </o:OLEObject> <![endif]><![endif]--><!--[if !vml]--><!--[endif]-->

      

     

      

    So we can now account for one of the four challenges:  the orderly nature of the orbits of planets in the solar system is due to conservation of energy and angular momentum during the collapse of the gas cloud from which they formed. 

      

     

      

    The direction of rotation is dictated by the angular momentum of the cloud. 

      

     

      

    The inclination of the planets is due to the flatness of the nebular disk after collapse.

      

     

  • Why are there two types of planets, terrestrial and Jovian?

      

     

      

    <!--[if !supportLists]-->A.  <!--[endif]-->The force of gravity due to the massive Sun draws the heavier, dense material of the terrestrial planets closer.

      

    <!--[if !supportLists]-->B.  <!--[endif]-->Initial orbits of the terrestrial planets bring them closer to the Sun where they fall into smaller orbits.

      

    <!--[if !supportLists]-->C.  <!--[endif]-->Near the Sun, only heavy elements and rocky material can condense from the solar nebula.

      

    <!--[if !supportLists]-->D.  <!--[endif]-->Jovian planets form first and draw much of the gaseous material to them via gravity, leaving only the heavier elements and rocky material behind.

      

     
  • So beyond the frost line, which lies between the orbits of Mars and Jupiter, temperatures had dropped enough for ices such as water, ammonia and methane to condense.

  • Accretion

      

    How to grow planetessimals:

      

     

      

    <!--[if !supportLists]-->·      <!--[endif]-->Initially small particles of gas and dust were able to stick together via their electrostatic attraction.

      

     

      

    <!--[if !supportLists]-->·      <!--[endif]-->As they grew larger, their gravity began to be strong enough to attract particles as well, and their growth accelerated.

      

     

      

    <!--[if !supportLists]-->·      <!--[endif]-->Once large enough, gravity pulls the planetessimal into a spherical shape.

      

     

      

    <!--[if !supportLists]-->·      <!--[endif]-->Once a planetessimal reaches a certain size (around 1 km) this process really takes off and it begins to gravitationally dominate everything around it.

      

     

      

    We can now account for the second important challenge of explaining our solar system, the division of planets into two basic types.

      

     

      

    Rocky, metallic material of the terrestrial planets could condense nearer to the Sun than the ices.   Hydrogen and helium gas remained gaseous throughout the solar system.

      

     

  • Forming the Jovian planets through nebular capture

      

     

      

    Once accretion finished building the seeds of the Jovian planets, their large masses meant that their gravity was strong enough to accumulate large amounts of the remaining nebular gases – i.e.  the force of gravity of the planet was stronger than that from the Sun at that point, so that the gas went from orbiting the sun to orbiting the planet.

      

     

      

    This process proceeded in basically the same way as the nebular collapse which formed the solar system, forming similar disks of material around the Jovian planets.  Some of the material contributed to the planet, and some to satellite systems through accretion.

      
       

     

      

    The Solar Wind blows out the Remaining Nebular Gases

      

     

      

    The solar wind is composed of charged particles from the Sun’s hot (millions of degrees K) corona which carry the Sun’s magnetic field. 

      

     

      

    We see evidence (T Tauri stars) that this solar wind is very strong in young stars.  Radiation pressure from the young sun is also important – photons have momentum.  

      

     

      

    These effects work to clear out the remaining gases, before they cool enough for ices to condense in the inner solar system.

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