6.2 Clues to the Formation of Our Solar Sytem Our Goals for Learning • What features of our solar system provide clues to how it formed? • What theory best explains the features of our solar system?
The Sun, planets, and large moons orbit and rotate in an organized way Counterclockwise seen from above the north pole)
Terrestrial planets are small, rocky, and close to the Sun. Jovian planets are large, gas-rich, and far from the Sun. (What about Pluto?)
According to the nebular theory our solar system formed from a giant cloud of interstellar gas (nebula = cloud)
• 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. What have we learned?
The cloud of gas that gave birth to our solar system resulted from the recycling of gas through many generations of stars within our galaxy.
Solar System Formation: 1- gravity forced the cloud to become smaller, it began to spin faster and faster 2- Collisions flatten the cloud into a disk.
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?
Fig 9.5 Inside the frost line: too hot for hydrogen compounds to form ices. Outside the frost line: cold enough for ices to form.
Gravity draws planetesimals together to form planets This process of assembly is called accretion
Why are there two types of planets? • Jovian planets form from because cooler temperatures allow H, He, and ice to condense forming a gas giant. • Terrestrial Planets form because the warmer temperatures only allowing metal and rock to condense
Review of nebular theory Fig 6.27
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.