1. Chapter 28 Solar System

2. Solar System

3. Solar System • Solar System: The Sun and all objects that orbit it. • Many theories as to how it may have formed… • Nebular theory: formed from a cloud of spinning gas & dust that condensed to create Solar System

4. Scientists think that gravity caused the nebula to shrink, forming Sun. • Left-over gas and dust then gathered to form the planets, moons, and other objects in our Solar System

5. Sun’s Family • Sun’s family includes nine eight planets, over 100 moons, & countless chunks of rock, dust, and ice… surrounded by one or more clouds of comets.

6. Planet… • Planet: objects changed their positions among the stars… ancient Greeks called them “planētēs” which means “wanderer” • Planets follow a curved path around Sun called an orbit.

7. Early Ideas on Universe… 2000BC: a flat Earth, with stars on a giant sphere moving around Earth. • 600BC: Pythagoras: round Earth, due to Lunar eclipse and ship’s mast evidence.

8. Retrograde Motion… • Retrograde motion: the apparent movement of a planet in the opposite direction across the sky. • The explanation of this kind of movement created the need for a better model of the solar system

10. 400BC: Aristotle: Earth was the center of the Universe… all objects orbited the Earth. • 1600AD: • Nicolus Copernicus: Sun is center of the Solar System. **Tycho Brahe, Johannes Kepler, Galileo, Sir Isaac Newton all further supported Copernicus. Copernicus' Model

11. Kepler’s Laws… • Kepler’s First Law: Each planet orbits the Sun in an ellipse, rather than a circle. • Eccentricity: the amount of variance from a perfect circle a planet undergoes during orbit. (0 = a perfect circle … 1 = a parabola)

12. Kepler’s 2nd Law… • Kepler’s 2nd Law: as planets move around the Sun, they sweep out equal amounts of area in equal time.

13. (The ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes): This is used to compare orbits of all celestial bodies… Kepler’s 3rd Law • Kepler’s 3rd Law: See the equation 

14. Newton described the planets orbits according to the Law of Universal Gravitation… He also determined “center of mass” as balance point between 2 orbiting objects. End of 29 – 1

15. Inner Planets • Mercury • Venus • Earth • Mars • All fairly small and rocky

16. Outer Planets • Jupiter • Saturn • Uranus • Neptune • Pluto • Gas giants (other than Pluto)

17. End of overview

18. Side view of entire Solar System, Fall, 1996 Orbits…

19. Gravity • Gravity: the force within the Universe that creates a pull on all objects. • Gravitational attraction pulls the planet towards the Sun as it move through space… keeping the planet from flying away. O

20. Circle vs. Ellipse • Earth (as well as all other planets) does not follow a perfect circle around the Sun. • Elliptical orbit due to perihelion and aphelion of planets.

21. Orbital Velocity • Orbital Velocity: the speed at which a planet orbits the Sun… changes due to proximity to Sun. • Fastest at perihelion …slowest at aphelion (Kepler 2nd)

22. As planet gets (IS) farther from the Sun, gravity lessens and planet slows…at aphelion • As the planet gets (IS) closer to the Sun, gravity increases, and planet’s orbital speed increases at perihelion. • This is why planets near the Sun orbit faster than those farther from Sun.

23. Planet km/sec km/min km/hr mi/hr Mercury 47.9 2,872.8 172,368.0 107,040.5 Venus 35.0 2,101.2 126,072.0 78,290.7 Earth 29.8 1,787.4 107,244.0 66,598.5 Mars 24.1 1,447.8 86,868.0 53,945.0 Jupiter 13.1 784.2 47,052.0 29,219.0 Saturn 9.7 580.2 34,812.0 21,618.3 Uranus 6.8 408.6 24,516.0 15,224.4 Neptune 5.5 327.0 19,620.0 12,184.0 Pluto 4.7 284.4 17,064.0 10,596.7 Mean Orbital Velocity - Planets in Solar System

24. End of orbital info

25. Deimos Phobos Other Moons in Solar System Io

26. Satellites… • Satellite: any object orbiting another object in space. • Moon is Earth’s only natural satellite. • 1610 Galileo four of Jupiter’s moons… “Galilean Moons”

27. Satellites of Inner Planets • Mercury: NONE • Venus: NONE • Earth: (1) Moon • Mars: (2) Deimos & Phobos Phobos

28. Mars’ moons • Both moons are rocky and odd shaped… not spherical. • Both moons orbit quickly, Phobos once each day, and Deimos takes just a little more than 1 day to orbit.

29. Outer Planet’s Moons… • Many more moons are found orbiting the gas giants… • (Most will be discussed later in the section, as we discuss each planet.)

30. Known Moons in Solar System • Planet # Moons Largest? Rings? Mercury 0 NONE NO Venus 0 NONE NO Earth 1 Moon NO Mars 2 Phobos NO Jupiter 63 Ganymede YES Saturn 59 Titan YES Uranus 27 Titania YES Neptune 13 Triton YES *Pluto 1 Charon NO ***All numbers accurate as of 2013(164 moons) * Pluto lost planet status in 2007

31. http://www.nasm.si.edu/ceps/etp/etp.htm

32. Measuring Distance in Space

33. Distance… • On Earth, meter, kilometer (inch, foot, mile) work fine… • Distance to stars is much too large to use “normal” units. • Proxima Centauri is nearest star to us 40,000,000,000,000km from Earth!!! (outside our solar system)

34. Light Year: the distance light will travel in one year. • Speed of light is 300,000km/s (583,152 m/h) • 1 light year equals 10,000,000,000,000km

35. Light from the Sun reaches the Earth in a little more than 8 minutes (150 Million km or 93 Million miles) • Light from Polaris (North Star) reaches the Earth in 470 years… it is 470 light years away.

36. Parallax • Parallax: an apparent change in position of a distant object when seen from 2 different places. • By checking parallax angle, the approximate distance can be determined. • Parallax

37. Astronomical Unit • Astronomical Unit: average distance from Sun to Earth …150,000,000km or 93,000,000 miles or 1AU • Used to measure distances within our Solar System.

38. Mercury • Distance from Sun: 0.4AU • Revolution: 0.24 years • Rotation: 59 days • Satellites: NONE • Atmosphere: very thin H and He • Temperatures: 450C (824F)“Daytime” to -170C (-274F)

39. Mercury…cont • Widest temperature range in the Solar System. • Wrinkled / shrunken surface due to extreme heating and internal cooling of the planet. • Most heavily cratered object in S.S. • Size: If Earth=baseball, Mercury=golf ball

40. Venus: “Earth’s Twin” • 3rd brightest object in sky • Distance: 0.7AU • Revolution: 0.62 years (225 days) • Rotation: 243 Days • Satellites: NONE • Atmosphere: very thick, CO2 and H2SO4 …90X Earth Atmosphere… only 2% Sunlight reaches Surface

41. Venus…cont • Temperatures: 470C (878F) at the surface… hottest planet in Solar System. • Surface has valleys, mountains, and plains…may have had liquid water oceans long ago. • Some volcanic activity.

42. Earth • Distance: 1AU • Revolution: 365.25 days • Rotation: 24 hours • Satellites: (1) Moon … 2nd brightest object in sky. • Atmosphere: N2, O2, & scarce others. • Temperature: Average 15C (58F)

43. Earth…cont • Only planet with water in 3 phases… solid, liquid, gas. • Tilted axis (23.50) creates seasons. • Only tectonically active planet in Solar System. • Moving plates, Volcanoes, & Weathering constantly change surface.

44. Mars: “War”/“the Red Planet” • Distance: 1.5AU • Revolution: 1.88 years • Rotation: 24.6 hours • Satellites: (2) Phobos & Diemos • Atmosphere: thin CO2 • Temperatures: 35C (85F) to –170C (-207F)

45. Mars…cont • Surface features: Iron oxide surface creates the red color. • Channels /canals: runoff or outflow of water created 3.5 to 4 billion years ago.

46. Olympus Mons towers 26 kilometers (16 miles) above the average surface elevation of Mars Olympus Mons is the largest volcano in the Solar system!

47. The canyons of Valles Marineris stretch nearly a fifth of the way around Mars (as long as the continental US from coast to coast!)

48. mission to Mars times... Mars, viewed from Hubble telescope.

49. Jupiter: the largest planet • Distance: 5.2Au • Revolution: 11.9 years • Rotation: 9.9 hours • Satellites: (63) 4 “Galilean Moons” and a ring system • Atmosphere: Mostly H and He… 24 to 30X our atmosphere. • Temperature: -153C (-244F)

50. Jupiter…cont • 4th brightest object in sky • Twice as massive as all other planets combined. • 1000X the size of Earth, 318X the mass of Earth • Huge magnetic field around Jupiter. • Great Red Spot is a storm that has 800km/hr winds, and it has been there since 1665 (Galileo)