Discovering the Universe Eighth Edition

1. Neil F. Comins • William J. Kaufmann III Discovering the Universe Eighth Edition CHAPTER 5 Formation of the Solar System

2. Essay Questions for this Lecture • What are the major similarities and differences between inner and outerplanets? • How did the solar system form? How does the condensation sequence theory explain the similarities and differences between Jovian and Terrestrial planets? • How do we detect other planetary systems around distant stars?  What are the strengths and limitations of each method?

3. WHAT DO YOU THINK? • How old is the Earth? How do we know??? • How old are the Sun and other planets? Were they created during the “Big Bang”? How do we know? • Have any Earthlike planets been discovered orbiting Sunlike stars? How can we tell?

4. In this chapter you will discover… • how the solar system formed • why the early solar system was much more violent than it is today • how astronomers define various types of objects in the solar system • how the planets are “grouped”

5. In this chapter you will discover… • how moons formed throughout the solar system • the “debris” in the solar system • that disks of gas and dust, as well as planets, have been observed around a growing number of stars • that newly forming stars & planetary systems are being observed

7. The solar system exhibits clear patterns of composition and motion. These patterns are far more important and interesting than numbers, names, and other trivia.

8. Planets are very tiny compared to distances between them.

9. Sun • Over 99.9% of solar system’s mass • Made mostly of H/He gas (plasma) • Converts 4 million tons of mass into energy each second

10. Mercury • Made of metal and rock; large iron core • Desolate, cratered; long, tall, steep cliffs • Very hot and very cold: 425°C (day), –170°C (night)

11. Venus • Nearly identical in size to Earth; surface hidden by clouds • Hellish conditions due to an extreme greenhouse effect • Even hotter than Mercury: 470°C, day and night

12. Earth Earth and Moon to scale • An oasis of life • The only surface liquid water in the solar system • A surprisingly large moon

13. Mars • Looks almost Earth-like, but don’t go without a spacesuit! • Giant volcanoes, a huge canyon, polar caps, and more • Water flowed in the distant past; could there have been life?

14. Jupiter • Much farther from Sun than inner planets • Mostly H/He; no solid surface • 300 times more massive than Earth • Many moons, rings

15. Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons • Io (shown here): Active volcanoes all over • Europa: Possible subsurface ocean • Ganymede: Largest moon in solar system • Callisto: A large, cratered “ice ball”

16. Saturn • Giant and gaseous like Jupiter • Spectacular rings • Many moons, including cloudy Titan • Cassini spacecraft currently studying it

17. Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon. Artist’s conception The Rings of Saturn

18. Cassini probe arrived July 2004. (Launched in 1997)

19. Uranus • Smaller than Jupiter/Saturn; much larger than Earth • Made of H/He gas and hydrogen compounds (H2O, NH3, CH4) • Extreme axis tilt • Moons and rings

20. Neptune • Similar to Uranus (except for axis tilt) • Many moons (including Triton)

21. Pluto and Eris • Much smaller than other planets • Icy, comet-like composition • Pluto’s moon Charon is similar in size to Pluto

22. Space isn’t empty… We know space is filled with gas and dust – the raw materials from which planetary systems form!

23. …and its composition changes Spectra of exploding and old stars shows heavier elements being ejected, too

24. Clues to Formation of our Solar System?

25. Clue #1: Motion of Large Bodies • All large bodies in solar system orbit in same direction & in nearly same plane. • Most also rotate in that direction.

26. Clue #2: Two Major Planet Types • Terrestrial planets are rocky, relatively small, & close to Sun. • Jovian planets are gaseous, larger, & farther from Sun.

27. Clue #3: Swarms of Smaller Bodies • Many icy comets, small “dwarf planets”, & rocky asteroids populate solar system in 3 areas

28. Notable Exceptions • Several exceptions to normal patterns need to be explained.

29. What theory best explains the features of our solar system?

30. According to the nebular theory, our solar system formed from a giant cloud of interstellar gas. (nebula = cloud)

38. Why are there two major types of planets?

39. The Laws of Physics • As gravity causes the cloud to contract, it heats up. (Conservation of Energy!) • As it contracts, it spins faster. (Conservation of Angular Momentum!) • As it spins and contracts, it flattens. • The temperature varies by distance

40. Inner parts of the disk are hotter than outer parts. Rock can be solid at much higher temperatures than ice. Temperature Distribution of the Disk and the Frost Line

41. 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

42. Formation of Terrestrial Planets • Small particles of rock and metal were present inside the frost line. • Planetesimals of rock and metal built up as these particles collided. • Gravity eventually assembled these planetesimals into terrestrial planets.

43. Tiny solid particles stick to form planetesimals. Summary of the Condensates in the Protoplanetary Disk

44. Gravity draws planetesimals together to form planets. This process of assembly is called accretion. Summary of the Condensates in the Protoplanetary Disk

45. Accretion of Planetesimals • Many smaller objects collected into just a few large ones.

46. Formation of Jovian Planets • Ice could also form small particles outside the frost line. • Larger planetesimals and planets were able to form. • The gravity of these larger planets was able to draw in surrounding H and He gases.

47. The gravity of rock and ice in jovian planets draws in H and He gases. Nebular Capture and the Formation of the Jovian Planets

48. Moons of jovian planets form in miniature disks.