What theory best explains the features of our solar system?
According to the nebular theory our solar system formed from a giant cloud of interstellar gas (nebula = cloud)
What have we learned? What features of our solar system provide clues to how it formed? Four major features provide clues: (1) The Sun, planets, and large moons generally rotate and orbit in a very organized way. (2) With the exception of Pluto, the planets divide clearly into two groups: terrestrial and jovian. (3) The solar system contains huge numbers of asteroids and comets. (4) There are some notable exceptions to these general patterns. What theory best explains the features of our solar system? The nebular theory, which holds that the solar system formed from the gravitational collapse of a great cloud of gas.
6.4 The Formation of Planets Our Goals for Learning Why are there two types of planets? Where did asteroids and comets come from? How do we explain the existence of our Moon and other “exceptions to the rules”? When did the planets form?
Four Unexplained Features of our Solar System √ Why do large bodies in our solar system have orderly motions? --> 2) Why are there two types of planets? 3) Where did the comets and asteroids come from? 4) How can we explain the exceptions the the ‘rules’ above?
Why are there two types of planet, when all planets formed from the same nebula?
Inside the frost line: too hot for hydrogen compounds to form ices. Outside the frost line: cold enough for ices to form. Fig 9.5
Tiny solid particles stick to form planetesimals.
Gravity draws planetesimals together to form planets This process of assembly is called accretion
Why are there two types of planets? 1.Jovian planets form from because cooler temperatures allow H, He, and ice to condense forming a gas giant. 2.Terrestrial Planets form because the warmer temperatures only allowing metal and rock to condense
We cannot find the age of a planet, but we can find the ages of the rocks that make it up We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it
The decay of radioactive elements into other elements is a key tool in finding the ages of rocks
Age dating of meteorites that are unchanged since they condensed and accreted tell us that the solar system is about 4.6 billion years old.