Astronomy 04 The Solar System

1. Astronomy 04The Solar System Chapter 7: “Other Worlds: An Introduction to the Solar System”

3. Terrestrial Planets

4. Jovian or Gas Giant Planets

8. The space between stars isn’t empty. It is filled with large amounts of gas and dust. This gas and dust sometimes is dense enough to form visible clouds called nebulae.

9. The Pleiades star cluster and surrounding nebula.

12. Catastrophic theoriescall upon unlikely sudden events to produce the solar system: Rene Descartes (1596-1650) proposed first catastrophic theory for origin of solar system: The Solar System formed when a “vortex” contracted and condensed.

13. Georges-Louis de Buffon (1707-1788): Proposed 2nd catastrophic theory: A passing star pulled matter from Sun which formed the solar system.

14. Evolutionary theories call upon common, gradual events to produce the solar system. Pierre-Simon de Laplace (1749-1827) proposed first evolutionary theory for origin of the solar system. - the nebular hypothesis.

15. The nebular hypothesis suggests the solar system formed from a rotating, collapsing cloud of gas and dust.

17. The solar nebula hypothesis suggests the solar system formed from a collapsing cloud of gas and dust about 4.5 billion years ago. As the rotating solar nebula collapsed under the influence of its own gravity, it formed a rotating disk.

18. The sun formed at the center of the disk where the pressures and temperatures were highest. The disk of gas and dust surrounding the newly formed sun organized itself into rings. The planets condensed and accreted from material in the rings.

20. The solar nebula hypothesis explains most of the observed characteristics of the solar system.

21. We date the age of Earth by determining the age of its oldest rocks. When a rock solidifies it incorporates known percentages of chemical elements. Some are radioactive and decay into other elements. The half-life of a radioactive element is the time it takes for half of its atoms to decay. The half life of Uranium 238 8 is 4.5 billion years.

22. If we studied a rock and found that only 50% of the Uranium 238 remained and the rest had become lead, we would conclude the rock is 4.5 billion years old. The oldest Earth rocks date to 4.0 billion years, the oldest moon rocks to 4.48 billion years and Mars rock to 4.5 billion years. Thus the solar system must be at least 4.48 billion years old.

23. The planet began forming by the process of condensation. The condensation sequence is the sequence in which different materials condensed from the gases of the solar nebula as we move away from the sun.

25. The condensation sequence suggests that the planets, forming at different distances from the sun, formed from different materials. The inner planets formed from metals and rocks while the outer planets formed from ices.

26. The inner – terrestrial planets – are dense rocky, metallic worlds. The outer planets far less dense gaseous, liquid worlds.

27. The correct sequence of planetary formation is: Condensation – accretion – planetesimnal – protoplanet.

28. In the development of a planet several processes operate: A particle grow by condensationwhen it adds matter one atom at a time from surrounding gas. Dust grains grew by this process.

29. Dust particles stuck together to form progressively larger lumps of materials. This process is called accretion. Eventually these lumps of material formed large objects called planetesimals.

30. Planetesimals eventually formed protoplanets. The decay of radioactive elements within a protoplanet generated heat sufficient to cause it to liquify. The molten protoplanet then underwent two processes: Differentiation – the separation of materials according to density. Metals sank while silicate material rise to the surface. Outgassing – the release of trapped gases to form an atmosphere.

31. Four processes helped clear the early solar system: radiation pressure – the force of sunlight. solar wind – the pressure of atomic particles streaming from the sun. heavy bombardment – debris being swept up by the planets gravitational ejection of material by larger planets.

32. Characteristics of the Planets: Terrestrial PlanetsGiant or Jovian Planets Near Sun Far from Sun Solid/Cratered Gaseous/Liquid Dense Not Dense Small Large Thin Atmospheres Thick Atmospheres Slow Rotators Fast Rotators Few Moons Many Moons No rings Rings