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The Planets page 694 Formation of the Solar System • The sun formed by gravitational contraction of a huge amount of interstellar matter around 5 billion years ago. We call this process accretion. The universe began primarily as hydrogen. • All other elements have to form in stars through nuclear fusion. Ellipse Activity Materials • • • • • Cardboard Pins (2) Pencil String (20-25cm) Paper • Place blank paper on cardboard and put pins 3cm apart • Tie string into circle with circumference 15-20 cm • Put string around pins and put a pencil in the string • Draw several ellipses • Vary the distance between the pins • OBSERVE Johann’s thing Keplers Laws of Planetary Motion Law 1: Each planet moves in an elliptical orbit having the sun at one focus. Law 2: An imaginary line from the sun to any planet sweeps out equal areas in equal time intervals. So . . . planets move faster when it is near the sun and more slowly when it is far away 2 3 p =d Law 3: The square of any planet’s period is proportional to the cube of the planet’s average distance from the Sun Period— • the time it takes for a planet to make one complete revolution Bode's Law • (That is actually neither Bode's not a Law.) – Begin a series of numbers with zero, add 3, then double the number hereafter – Add 4 – Divide by 10 Original series Add 4 Divide by 10 0 4 .4 3 7 .7 6 10 1.0 12 16 1.6 24 28 2.8 48 52 5.2 96 100 10.0 192 196 19.6 384 388 38.8 768 772 77.2 • • • • • • • • • • Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Bode's Actual 0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 30.6 38.8 0.39 0.72 1.0 1.52 2.77 5.20 9.54 19.18 30.07 39.44 Stars remain relatively fixed in the sky, but the planets wander The definition of a planet recently changed Planet qualifications • Must orbit the sun • Must have a basically round shape (hydrostatic equilibrium • Must have cleared its orbit of other objects – Pluto misses the third—the Kuiper Belt My very excellent mother just served us nine pizzas. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (Pluto) Two groups of planets: Inner & Outer Inner planets: The four planets closest to the sun • Mercury, Venus, Earth, Mars • also called the Terrestrial planets-small, rocky, high density • The mass of a body cannot be found unless it has a Satellite Mercury • Fastest planet • Rotation 88 days • Rotates 3 x's for every 2 revolutions so daytime is very hot, 430 C • Very little atmosphere-- nighttime cold, -170C • Mariner probe visits –used to determine mass Venus Usually the brightest planet in the sky Brighter than Mercury and seen near the Sun at sunup or sunset Venus is sometimes called Earth's twin Similar size, density, and distance from the sun But there are differences Venus Greenhouse Effect Very dense atmosphere, and opaque cloud cover severe greenhouse effect Sulfuric acid rain Very hot place 460 C 1 rotation = 243 Earth days 1 revolution = 225 Earth days So. . . a day is longer than a year Earth --The Blue Planet Earth is special because water may exist as a liquid and so it is conducive to life 71% water Mars—The Red Planet Red is from FeO iron oxide—rust Mass is 1/9 of Earth A little more than 1/2 Earth's size Atmosphere is 95% CO2 Two small moons: Phobos and Deimos— potato shaped Olympus Mons: • largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain • base is more than 500 km in diameter • rimmed by a cliff 6 km (20,000 ft) high (right) Erosion on Mars There is very clear evidence of erosion in many places on Mars including large floods and small river systems (left) At some time in the past there was clearly some sort of fluid on the surface