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Warm Up Questions 1. Which planet is bigger, Mercury or Jupiter ? 2. Are the gas giant planets closer to the Sun than the rocky planets (yes/no)? 3. How many planets are in the Solar System? 4. Is the Sun bigger, smaller, or the same size as the Moon? 5. What is the difference between the Solar System and the Milky Way Galaxy (just one sentence) ? The Ordered Solar System Ka Hana ‘Imi Na‘auao – A Science Careers Curriculum Resource Go to: www.cds.hawaii.edu/kahana 1 Why are there only 8 planets now? 2 What is a planet? • In August of 2007 the International Astronomical Union redefined what a planet is (no official scientific definition of a "planet" existed before). A planet: 1. Is a body that orbits the sun (this definition only applies to our Solar System) 2. Is large enough for its own gravity to make it round 3. And has "cleared its neighborhood" of smaller objects • So a new the category of dwarf planet was created, which currently includes Pluto, Eris*, and Ceres**. Three types of objects orbit our Sun: 1. Planets 2. Dwarf Planets • Plutoids 3. Small solar system bodies 3 *Eris is the largest known dwarf planet in the Solar System and the ninth largest body known to orbit the Sun. Its distance from the Sun is 97 AU. **Ceres is the smallest identified dwarf planet in the Solar System and, 4 because it’s the largest asteroid, the only dwarf planet in the asteroid belt. Only 5 Dwarf Planets recognized so far but there may be as many as 200 What is a Dwarf Planet? • Celestial body orbiting the Sun • Massive enough to be rounded by its own gravity • BUT has NOT cleared its neighboring region of planetesimals • Is not a satellite Pluto, approximate true color A plutoid is a dwarf planet beyond the orbit of Neptune 5 Makemake, (Artist’ (Artist’s conception) Ceres, seen through Eris, Eris, seen through (Hubble telescope) (Hubble telescope) Haumea, Haumea, with its 2 moons, Hi‘ Hi‘iaka and Namaka (Artist’ (Artist’s conception) 6 Pacific Island Names for Planetary Objects Pacific Island Names for Planetary Objects • Haumea is the Hawaiian goddess of childbirth and fertility. • The the moons "Hi‘iaka" and "Namaka” are named after after two of Haumea's daughters. • Makemake is the creator of humanity in the mythos of the Rapanui, the native people of Easter Island. The name choice preserves the planetary object's connection with Easter. 7 8 Terrestrial vs. vs. Gaseous Planets 3. What are Small Solar System Bodies? Terrestrial • Neither a planet nor a dwarf planet • All other objects orbiting the Sun Gaseous • Jupiter, Saturn, Uranus, Neptune 1. Gaseous, has more He and H • Mercury, Venus, Earth, Mars 1. Rocky → More dense • All minor planets except dwarf planets • Asteroids (except Ceres, the largest) • Comets → Less dense (Saturn would float) 2. Smaller 3. More closely spaced 4. Closer to the Sun • Not massive enough to be rounded by its own gravity 2. Larger 3. Spaced farther apart 4. Farther from the Sun 9 10 Jovian Planets, or Gas Giants Terrestrial Planets Uranus Neptune Saturn Jupiter Mars Venus Mercury 11 From Nick Strobel’s Astronomy Notes at www.astronomynotes.com 12 From Nick Strobel’s Astronomy Notes at www.astronomynotes.com Do you see patterns or anomalies in these data? On which planet would you weigh the most? 13 The Milky Way Galaxy 100,000 light years across 1,000 light years thick 200 billion stars You are here 15 14