1. The Solar System 09.19.07 / 09.20.07

2. Essential Questions What are distinguishing features of solar system bodies? What are distinguishing features of solar system bodies? What are Kepler’s laws and how do they apply to planetary motion? What are Kepler’s laws and how do they apply to planetary motion? What is the nebular hypothesis? What is the nebular hypothesis?

3. Overview of the solar system  Solar system includes Sun Sun Eight planets and their satellites Eight planets and their satellites Asteroids Asteroids Comets Comets Meteoroids Meteoroids

4. Kuiper Belt 2.8 - 4.6 billion miles away 2.8 - 4.6 billion miles away Probably tens-of-thousands of rocky, icy objects Probably tens-of-thousands of rocky, icy objects Includes Pluto Includes Pluto Discovered circa 1992 Discovered circa 1992 Predicted in 1951 by Gerald Kuiper Predicted in 1951 by Gerald Kuiper

5. The solar system

6. The orbits of most asteroids lie between Mars and Jupiter

7. Minor members of the solar system  Asteroids Most lie between Mars and Jupiter Most lie between Mars and Jupiter Small bodies – largest (Ceres) is about 620 miles in diameter Small bodies – largest (Ceres) is about 620 miles in diameter Some have very eccentric orbits Some have very eccentric orbits Irregular shapes Irregular shapes Origin is uncertain Origin is uncertain

8. Image of asteroid 951 (Gaspra)

9. Minor members of the solar system  Comets Often compared to large, "dirty snowballs" Often compared to large, "dirty snowballs" Composition Composition Frozen gases Frozen gases Rocky and metallic materials Rocky and metallic materials

10. Minor members of the solar system  Comets Origin Origin Not well known Not well known Form at great distance from the Sun Form at great distance from the Sun

11. Comet Hale-Bopp Comet Hale-Bopp

12. Minor members of the solar system  Meteoroids Called meteors when they enter Earth's atmosphere Called meteors when they enter Earth's atmosphere A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet's path A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet's path Meteoroids are referred to as meteorites when they are found on Earth Meteoroids are referred to as meteorites when they are found on Earth

13. Overview of the solar system  A planet's orbit lies in an orbital plane Similar to a flat sheet of paper Similar to a flat sheet of paper The orbital planes of the planets are inclined The orbital planes of the planets are inclined Planes of seven planets lie within 3 degrees of the Sun's equator Planes of seven planets lie within 3 degrees of the Sun's equator Mercury's is inclined 7 degrees Mercury's is inclined 7 degrees Pluto's is inclined 17 degrees (That crazy Pluto) Pluto's is inclined 17 degrees (That crazy Pluto)

14. Overview of the solar system  Two groups of planets occur in the solar system Terrestrial (Earth-like) planets Terrestrial (Earth-like) planets Mercury through Mars Mercury through Mars Small, dense, rocky Small, dense, rocky Low escape velocities Low escape velocities

15. Overview of the solar system  Two groups of planets occur in the solar system Jovian (Jupiter-like) planets Jovian (Jupiter-like) planets Jupiter through Neptune Jupiter through Neptune Large, low density, gaseous Large, low density, gaseous Massive Massive Thick atmospheres composed of hydrogen, helium, methane, and ammonia Thick atmospheres composed of hydrogen, helium, methane, and ammonia High escape velocities High escape velocities Pluto not included in either group (oddball) Pluto not included in either group (oddball)

16. The planets drawn to scale

17. Evolution of the planets  Nebular hypothesis Planets formed about 5 billion years ago Planets formed about 5 billion years ago Solar system condensed from a gaseous nebula Solar system condensed from a gaseous nebula  As the planets formed, the materials that compose them separated Dense metallic elements (iron and nickel) sank toward their centers Dense metallic elements (iron and nickel) sank toward their centers Lighter elements (silicate minerals, oxygen, hydrogen) migrated toward their surfaces Lighter elements (silicate minerals, oxygen, hydrogen) migrated toward their surfaces

19. Kepler’s Laws Law 1: The planet orbit is ellipses with the Sun at one of two foci Law 1: The planet orbit is ellipses with the Sun at one of two foci Law 2: The line connecting the planet to the Sun sweeps equal areas in equal time Law 2: The line connecting the planet to the Sun sweeps equal areas in equal time Law 3: The periods of planets’ revolutions is proportional to their distances from the Sun Law 3: The periods of planets’ revolutions is proportional to their distances from the Sun

20. Law 1 http://astro.isi.edu/notes/gravity.html

21. Law 2 http://burro.astr.cwru.edu/Academics/Astr221/Gravity/kepler2.htm

22. Law 3 http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html

23. Eight or Nine?  Pluto Discovered in 1930 Discovered in 1930 Highly eccentric orbit causes it to occasionally travel inside the orbit of Neptune, where it resided from 1979 through February 1999 Highly eccentric orbit causes it to occasionally travel inside the orbit of Neptune, where it resided from 1979 through February 1999 Moon (Charon) discovered in 1978 Moon (Charon) discovered in 1978

24. Pluto and its moon Charon as compared to the size of Earth

25. A decision to make With the discovery of the Kuiper Belt, astronomers need to make on of two choices: With the discovery of the Kuiper Belt, astronomers need to make on of two choices: allow the possibility of many, many more planets allow the possibility of many, many more planets create a more restrictive definition of planet create a more restrictive definition of planet They chose this second option They chose this second option They then created possible definitions They then created possible definitions

26. Potential definition 1 A planet would need to a) revolve around a star, b) be massive enough to have formed into a round shape, c) not be a moon, and d) not be another star A planet would need to a) revolve around a star, b) be massive enough to have formed into a round shape, c) not be a moon, and d) not be another star This option would have resulted in 12 planets, with more possible in the future This option would have resulted in 12 planets, with more possible in the future

27. Potential definition 2 The same as the first with one addition The same as the first with one addition the planet must have “cleared the neighborhood around its orbit.” the planet must have “cleared the neighborhood around its orbit.” Because Pluto’s orbit crosses paths with Neptune, it would not qualify Because Pluto’s orbit crosses paths with Neptune, it would not qualify This definition results in 8 planets This definition results in 8 planets This is the one the International Astronomical Union chose to accept This is the one the International Astronomical Union chose to accept Pluto hasn’t changed, just our definition of planet Pluto hasn’t changed, just our definition of planet

29. Light pollution http://epod.usra.edu/archive/epodviewer.php3?oid=92448

30. Source: University of Hawaii

31. Houses cause pollution too

32. Better lighting

33. Source: NASA see also p. 664 in home text

34. Resources International Dark-Sky Society International Dark-Sky Society International Astronomical Union International Astronomical Union Light Pollution Abatement Program (LPAP) Canada Light Pollution Abatement Program (LPAP) Canada