1. Lecture 31: The Family of the Sun Astronomy 161 – Winter 2004

2. Key Ideas: The Solar System contains: The Sun Terrestrial Planets Jovian Planets Pluto Giant Moons Asteroids, Icy Bodies, Comets, & Meteoroids The planets all lie in nearly the same plane and orbit in the same general direction.

3. The Golden Age of Exploration The Solar System has been explored with robotic spacecraft & astronauts: Landed men on the Moon Robotic landers on Moon, Venus, & Mars Returned rocks from the Moon (~382 kg) Probed Atmospheres of Venus, Mars, & Jupiter Flown spacecraft by all planets except Pluto Mapped Venus with radar Flown by asteroids & comets, landing on one asteroid

4. Magellan Venus Cassini & Huygens Mars Sojourner Pioneer 10 & 11 Voyager 1 & 2 Apollo 11-17

5. The Family of the Sun The Sun: a middle-aged, average sized star The Terrestrial Planets: Rocky Planets: Mercury, Venus, Earth & Mars The Jovian Planets: Gas Giants: Jupiter, Saturn, Uranus & Neptune Pluto: fits into neither category Small Icy & Rocky Bodies: Icy: Icy Moons, Kuiper Belt Objects, & Comets Rocky: Giant Moons, Asteroids & Meteoroids

6. The 9 Planets, in order: Planets: Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Mnemonic: My Very Educated Mother Just Served Us Nine Pizzas

7. Relative Sizes of the Planets

8. Basic Properties of the Planets Locations: Terrestrial in the inner solar system: 0.4-1.5AU Jovian in the outer solar system: 5-30 AU All orbit in the same direction & same plane: Orbit counterclockwise, in the same sense as the rotation of the Sun. All except Pluto orbit very near the Ecliptic plane. Provides clues to Solar System formation.

9. Pluto Neptune Uranus Saturn Jupiter Mars Earth Venus Mercury

10. Pluto Ecliptic Plane

11. The Solar System, by mass The contents of the Solar System, ordered by their total mass in Earth masses: Sun: 330,000 M Earth 4 Jovian Planets: 447 M Earth total 4 Terrestrial Planets: 1.985 M Earth total Giant Moons: 0.105 M Earth total Pluto, the icy oddball planet: 0.002 M Earth Rest of the contents make a tiny contribution.

12. The Sun The Sun is a middle-aged, average-sized star. Mostly Hydrogen & Helium Contains 99.8% the mass of the Solar System about 4.6 Gyr old The Sun shines because it is hot: Surface (photosphere) is ~6000 K Radiates mostly Visible light plus UV & IR Kept hot by nuclear fusion in its core: Builds Helium from Hydrogen fusion.

14. The Jovian Planets Jupiter, Saturn, Uranus & Neptune Largest Planets: at least 15 times mass of Earth. Jupiter, largest, is 318 Earth Masses Only in the outer solar system (5 to 30 AU) Gas Giants (“Jupiter-like”): No Solid Surfaces (mostly atmosphere) Mostly Hydrogen & Helium Rocky/icy inner cores Low density: 0.7 to 1.7 g/cc (water is 1 g/cc)

15. The Jovian Planets Jupiter (318 M  ) Uranus (15 M  ) Saturn (95 M  ) Neptune (17 M  )

17. Terrestrial Planets Mercury, Venus, Earth & Mars “Earth-Like” Rocky Planets Largest is Earth Only in the inner solar system (0.4 to 1.5 AU) Rocky Planets: Solid Surfaces Mostly silicates and iron High Density: 3.9-5.5 g/cc (rock & metal) Earth, Venus, & Mars have atmospheres

18. The Terrestrial Planets Earth (1 M  ) Mars (0.11 M  ) Venus (0.82 M  ) Mercury (0.055 M  )

19. Solid inner core Liquid outer core

20. The Giant Moons Natural satellites orbiting planets. Giant Moons: Earth: The Moon Jupiter: Io, Europa, Ganymede, & Callisto (the Galilean moons) Saturn: Titan Neptune: Triton Many smaller moons, both rocky & icy. Only Mercury & Venus have no moons.

21. The Giant Moons

22. Pluto: The Planet that Doesn’t Fit Pluto is neither a Terrestrial nor Jovian Planet. Smallest of the planets Intermediate Density: 1.8 g/cc (mostly icy) Pluto’s orbit is also odd: The most elliptical orbit of all the planets The most highly inclined: ~17º from the Ecliptic. Largest of a distinct class of objects, but still a “planet”.

23. Distant Pluto Pluto Charon Pluto’s Moon Hubble Reconstruction of Pluto

24. Small Icy Bodies Pluto is the largest of a class of icy bodies: Found only in the outer solar system Densities of 1.2 to 2 g/cc (like ices) Examples: Triton, large moon of Neptune Charon, Pluto’s large moon Trans-Neptunian Objects (Kuiper Belt Objects & Plutinos)

26. Triton

27. The Leftovers (Minor Bodies) Asteroids: Range from 500km (Ceres) to large boulders Made of rock (density 2-3 g/cc) Meteoroids: Bits of rock and metal Range in size from grains of sand to boulders Comets: Composite rock & ice “dirty snowballs” Longs tails of gas & dust are swept off them when they pass near the Sun.

29. Asteroids 253 Mathilde 951 Gaspra 243 Ida

30. Meteor burning up in the atmosphere.

31. Comet Hale-Bopp

32. 5 km Nucleus of Comet Halley