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Moons The satellites of the solar system Moons of our solar system • As of July 2009, there are 336 known natural moons in our solar system. 168 moons orbit the "full-size" planets (Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), while 6 moons orbit the smaller "dwarf planets" (Ceres, Pluto, Haumea, Makemake, and Eris). Others orbit asteroids and Trans-Neptunian objects. • Mercury and Venus have no moons Which planet? How many? • • • • • • • • • Earth – 1 moon – Luna Mars – 2 moons Jupiter – 63 moons Saturn – 62 moons Uranus – 27 moons Neptune – 13 moons Pluto – 3 moons Haumea – 2 moons Eris – 1 moon • When we consider that Saturn could have as many as 1 million moons, the question arises, “What constitutes a moon?” What is a moon? • A moon is a natural satellite of a celestial body. It can orbit a planet, an asteroid, etc. • Usually a moon orbits either a planet or a dwarf planet • The official size of a moon is still being debated and it does not appear that it will be settled soon. Ten largest moons in the solar system 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Ganymede - Jupiter - 5268 kilometers in diameter Titan - Saturn - 5150 kilometers in diameter Callisto - Jupiter - 4806 kilometers in diameter Io - Jupiter - 3636 kilometers in diameter Moon - Earth - 3474 kilometers in diameter Europa - Jupiter - 3122 kilometers in diameter Triton - Neptune - 2706 kilometers in diameter Titania - Uranus - 1578 kilometers in diameter Rhea - Saturn - 1528 kilometers in diameter Oberon - Uranus - 1523 kilometers in diameter Oddball moons • Triton travels around Neptune backwards and could be a captured body from the Kuiper Belt. In fact, Triton may look a lot like Pluto. • Titan, the second largest moon in the solar system, is an icebox Earth, with a thick atmosphere, methane meteorology, and youthful surface. • Ganymede’s icy mantle could contain a liquid ocean layer, but evidence for that is not conclusive. Which is the largest moon in the solar system? a. b. c. d. Luna Ganymede Titan Triton The planet with the most moons is a. b. c. d. Saturn Jupiter Neptune Venus A moon is…. a. Anything that orbits a celestial body that’s bigger than a breadbox b. a natural satellite of a celestial body c. Bigger than a truck d. A natural satellite of a celestial body that orbits a planet in the same direction as the planet’s rotation The moon that orbits it’s planet in the direction opposite the planet’s rotation is a. b. c. d. Ganymede Io Triton Titan How do we know what we know about the moons? • • • • • • • Mariner 1-10 – 1962 to 1973 Pioneer 10 and 11 – 1972 and 1973 Voyager 1 & 2 – 1977 Galileo – 1989 Cassini - 1997 LRO (Lunar Reconnaissance Orbiter) - 2009 Hubble (1990) and Kepler (2009) Luna – the Earth’s moon Luna • The Earth’s only natural satellite • Second brightest object in our sky • Albedo of Luna is .07 (reflects 7% of the light that hits it), surface is color of charcoal • Fifth largest satellite in the solar system • 1/4th the diameter of the Earth • 1/81st of the Earth’s mass • Synchronous rotation with the Earth – we always see the same side of the moon The two sides of the moon The side we always see The “dark side of the moon” Actually we see more than we know… • Due to the lunar libration, or a slow rocking back and forth motion, we actually see about 59% of Luna’s surface on the side that faces us. The side hardly anyone sees… • Taken by Clementine spacecraft, this is a mosaic picture of the south pole of Luna What we see changes… • What we see depends on the phase of the moon from the sliver of a new moon to a full moon when the moon is behind us, reflecting the Sun’s light What we see also depends on how close Luna is to the Earth… What is the cause of the rocking back and forth motion? • May be due to extended influence of Earth’s gravity on the moon while it is retreating from the Earth • Moon’s core is actually off-center What are the numbers? • Moon Numbers Size: 3,476.2 kilometers -- 0.2725 Earths -14th largest solar system body Orbit: 384,400 kilometers from Earth Calendar: 1 lunar day = 29.53 Earth days • Our Moon is retreating (moving away) at about 3.8 centimeters (1.5 inches) per year. Our moon orbits the Earth a. b. c. d. 24,000 km away. 384,000 km away. Whenever it feels like it. Every couple of months or so. Luna is the ________ largest satellite in the solar system. a. b. c. d. Second Third Fourth Fifth Internal structure of our Moon • Geologically distinct mantle, crust and core • Solid inner core is probably high in iron content approximately 240 km in diameter • Liquid iron outer core and an area of partially melted boundary between core and mantle Crust • The dark, featureless areas are called maria, thought by early observers to be seas on the surface • Mare are solidified pools of basaltic lava • Maria are found almost exclusively on the side facing the Earth and make up 31% of the surface • Lighter colored regions, terrae, are highlands • It is not made of cheese…sorry • Neither is there a man in the moon Where did it come from? Three traditional theories 1.Moon and Earth developed at the same time (condensation hypothesis) 2.Moon was made of material that came from the Earth (fission hypothesis) 3.Moon was captured by the Earth’s gravity (capture hypothesis) Large-impact hypothesis • Large celestial body struck the Earth in it’s early stages • Most of the iron merged with Earth and differentiated into the core • Most iron poor debris formed a ring around Earth that accreted into Luna • Evidence? Composition of lunar rocks, signs of intense heat,