Our Solar System and Its Origin

1. Our Solar System and Its Origin

2. 6.1 A Brief Tour of the Solar System Our Goals for Learning • What does the solar system look like?

3. What does the solar system look like?

4. The planets are tiny compared to the distances between them (a million times smaller than shown here), but they exhibit clear patterns of composition and motion. The patterns are far more important and interesting than numbers, names, and other trivia

5. Recall scale of solar system

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

7. 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

8. 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)

9. Venus • nearly identical in size to Earth; surface hidden by thick clouds • hellish conditions due to an extreme greenhouse effect: • even hotter than Mercury: 470°C, both day and night • atmospheric pressure equiv. to pressure 1 km deep in oceans • no oxygen, no water, … • perhaps more than any other planet, makes us ask: how did it end up so different from Earth?

10. Earth and Moon to scale • Earth • An oasis of life • The only surface liquid water in the solar system; about 3/4 of surface covered by water • A surprisingly large moon

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

12. Jupiter • Much farther from Sun than inner 4 planets (more than twice Mars distance) • Also very different in composition: mostly H/He; no solid surface. • Gigantic for a planet: 300  Earth mass; >1,000  Earth volume. • Many moons, rings…

13. Moons can be as interesting as the planets themselves, especially Jupiter’s 4 large “Galilean moons” (first seen by Galileo) • Io (shown here): active volcanoes all over • Europa: possible subsurface ocean • Ganymede: largest moon in solar system — larger than Mercury • Callisto: a large, cratered “ice ball” with unexplained surface features

14. Saturn • Giant and gaseous like Jupiter • most spectacular rings of the 4 jovian planets • many moons, including cloud-covered Titan • currently under study by the Cassini spacecraft

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

16. Saturn Cassini probe arrived July 2004 (Launched in 1997)

17. Uranus • much smaller than Jupiter/Saturn, but still much larger than Earth • made of H/He gas, hydrogen compounds (H2O, NH3, CH4) • extreme axis tilt — nearly tipped on its “side” — makes extreme seasons during its 84-year orbit. • moons also tipped in their orbits…

18. Neptune • Very similar to Uranus (but much smaller axis tilt) • Many moons, including unusual Triton: orbits “backward”; larger than Pluto.

19. Pluto • A “misfit” among the planets: far from Sun like large jovian planets, but much smaller than any terrestrial planet. • Comet-like composition (ices, rock) and orbit (eccentric, inclined to ecliptic plane, long -- 248 years). • Its moon Charon is half Pluto’s size in diameter • Best current photo above; New Horizons mission launch 2006, arrival 2015…

21. What have we learned? • What does the solar system look like? • Our solar system consists of the Sun, nine planets and their moons, and vast numbers of asteroids and comets. Each world has its own unique character, but there are many clear patterns among the worlds.

22. 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?

23. What features of our solar system provide clues to how it formed?

24. The Sun, planets, and large moons orbit and rotate in an organized way counterclockwise seen from above the north pole)

25. Terrestrial planets are small, rocky, and close to the Sun. Jovian planets are large, gas-rich, and far from the Sun. (What about Pluto?)

27. Rocky asteroids between Mars & Jupiter Icy comets in vicinity of Neptune and beyond Asteroids and comets far outnumber the planets and their moons

28. A successful theory of solar system formation must allow for exceptions to general rules

29. Summary: Four Major Features of our Solar System

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

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

32. • 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?

33. 6.3 The Birth of the Solar System • Our Goals for Learning • Where did the solar system come from? • What caused the orderly patterns of motion in our solar system?

34. Where did the solar system come from?

35. 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.

36. What caused the orderly patterns of motion in our solar system?

38. As gravity forced the cloud to become smaller, it began to spin faster and faster

39. As gravity forced the cloud to become smaller, it began to spin faster and faster Conservation of angular momentum

40. As gravity causes cloud to shrink, its spin increases Conservation of angular momentum

41. Collisions flatten the cloud into a disk. The orderly motions of our solar system today are a direct result of the solar system’s birth in a spinning, flattened cloud of gas.

42. Collisions between gas particles in cloud gradually reduce random motions

43. Collisions between gas particles also reduce up and down motions

44. Spinning cloud flattens as it shrinks

45. We see plenty of evidence for spinning disks of gas andf dust around other stars, especially newly formed stars

46. What have we learned? • Where did the solar system come from? • The cloud of gas that gave birth to our solar system was the product of recycling of gas through many generations of stars within our galaxy. This gas consisted of 98% hydrogen and helium and 2% everything else combined.

47. What have we learned? • What caused the orderly patterns of motion in our solar system? • A collapsing gas cloud naturally tends to heat up, spin faster, and flatten out as it shrinks in size. Thus, our solar system began as a spinning disk of gas. The orderly motions we observe today all came from the orderly motion of this spinning disk of gas.

48. 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?

49. 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?

50. Why are there two types of planet, when all planets formed from the same nebula?