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Structure and Origin of the Solar System
Transcript of Structure and Origin of the Solar System
terrestrial and jovian. The Solar System is littered with cosmic debris. The objects in the Solar System have a common age of about 4.6 billion years. watch?v=gvSUPFZp7Yo&feature=related http://www.redshift-live.com/binaries/asset/image/17231/image/The_axes_of_rotation_of_the_eight_planets.jpg The terrestrial planets are Mercury, Venus, Earth and Mars. They are
close to the Sun
have very few moons The jovian planets are Jupiter, Saturn, Uranus and Neptune. They are
far from the Sun
have mulitudes of moons comet asteroid Ages of rocks in the solar system are based on radioactive dating. If we look at all the observed features of our Solar System, they suggest a likely story of how the Solar System formed.
The formation theory that we will describe is called the Solar Nebula Hypothesis: About 4.6 billion years ago, a slowly rotating cloud of gas and dust began to contract and flatten. The hottest part at the center formed the Sun, and planets grew from the rest of the debris in the spinning disk. How do the observations support this theory?
common revolution and rotation suggests initial spinning of cloud
all planets close to the ecliptic plane suggests the flattening (obedience to laws of physics)
the composition of the planets (rocky close to the Sun, gaseous far away) is consistent with high temperatures near the center of the Solar nebula, and low temperatures further away
debris in the solar system suggests that large bodies built up from smaller ones How did planets form? When the Sun first began shining, the solar nebula surrounding it was entirely gaseous. Solid particles could only condense from the vapor once temperatures cooled. Temp (K) Material
1500 Metal Oxides
1300 Iron, Nickel
175 H2O ice
65 argon-neon ice At temperatures higher than the ones listed, each material remains vaporized and can't be incorporated into planets that are growing. Condensation Sequence This explains why planets like Jupiter, Saturn, Uranus and Neptune could grow so large and are made of light elements--they could sweep up these ices whereas planets forming closer to the Sun could not--those materials remained vaporized. What happened next? Small clumps began to collide with one another and stick together in a process called accretion (the building up of a large thing from picking up small things). Planetessimals grow by accretion into larger bodies called protoplanets.
The protoplanets continue to grow in size due to collisions with other planetessimals, which sometimes cause cratering. We are sure that collisions are a part of the planet forming process because we see cratered surfaces.
The protoplanets differentiate; their interiors heat (by radioactivity) and so heavy materials sink and light materials float to the surface. Radiation pressure from the Sun eventually clears away all remaining small debris, leaving behing the planets, a belt of asteroids separating the terrestrial planets from the jovian ones, surrounded by a spherical cloud of icy bodies called comets. Yes! Evidence for planets orbiting other stars
wobbling stars indicating the presence of massive, unseen companions or noticing eclipses of the stars
dusty, planet forming disks around some stars
direct imaging of other planets (new!) watch?v=n_jlpkEobNY watch my officemate from U Hawai'i talk about direct imaging of a planet in another solar system! This is long, but interesting http://csep10.phys.utk.edu/lightcone/demo/vlab/vlab3/neb_hypothesis.swf