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Wednesday, November 2, 2011
The Origin of the Solar System
Chapter 19
Wednesday, November 2, 2011
I. Theories of Earth’s Origin A. Early Hypotheses B. The Solar Nebula Hypothesis
II. A Survey of the Solar System A. A General View B. Two Kinds of Planets C. Space Debris D. The Age of the Solar System
Outline
Wednesday, November 2, 2011
III. The Story of Planet Building A. A Review of the Origin of Matter B. The Chemical Composition of the Solar Nebula C. The Condensation of Solids D. The Formation of Planetesimals E. The Growth of Protoplanets F. Is There a Jovian Problem? G. Explaining the Characteristics of the Solar
System H. Clearing the Nebula
IV. Planets Orbiting Other Stars A. Planet-Forming Disks around Other Suns B. Extrasolar Planets
Outline (continued)
Wednesday, November 2, 2011
Two Kinds of PlanetsPlanets of our solar system can be divided into two very different kinds:
Terrestrial (earthlike) planets: Mercury,
Venus, Earth, Mars Jovian (Jupiter-like) planets: Jupiter, Saturn, Uranus,
NeptuneWednesday, November 2, 2011
Terrestrial PlanetsFour inner planets of the solar system
Relatively small in size and mass (Earth is the largest and most massive)
Rocky surface
Surface of Venus can not be seen directly from Earth because of its
dense cloud cover.Wednesday, November 2, 2011
Craters on Planets’ SurfacesCraters (like on our Moon’s surface) are common throughout the Solar System.
Not seen on Jovian planets because they don’t have a solid surface.
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The Jovian PlanetsMuch lower
average density
All have rings (not only Saturn!)
Mostly gas; no solid surface
Wednesday, November 2, 2011
Space DebrisIn addition to planets, small bodies orbit the sun:
Asteroids, comets, meteoroids
Asteroid Eros, imaged by the NEAR spacecraft
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The asteroid Ida and its tiny “moon”: non-spherical shape due to small mass
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Asteroid Belt between Mars and Jupiter
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Factoids:• Although it might have once contained as much as 10 Earth-masses, the asteroid belt is now estimated to contain something like 1/1000 the mass of the Earth.• A network of telescopes is searching for near-earth asteroids.
Wednesday, November 2, 2011
Comets
Wednesday, November 2, 2011
Comets
Icy nucleus, which evaporates and gets blown into space by solar wind pressure.
Wednesday, November 2, 2011
Comets
Mostly objects in highly elliptical orbits, occasionally coming close to the sun.
Icy nucleus, which evaporates and gets blown into space by solar wind pressure.
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Oort Cloud
In 1950, Jan Oort noticed that: 1. None of the known comets come from interstellar space. 2. There is a strong tendency for cometary orbits to reach out to about 50,000 AU 3. Comets come from random directions
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Comet Ikeya-Seki
comets do not whiz through sky quickly like a meteor.
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Sketch of the Oort cloud and Kuiper belt
Warning: not drawn to scale
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Kuiper Belt:
• Just past the orbit of Neptune (30AU)• 30-50 AU• ~1,000 known members; examples:
Pluto (at 40 AU)Quaoar (at 50 AU; ½ size of Pluto)2003 UB313 (97 AU)Eris (size of Pluto at 96.6 AU)
• About 35,000 objects larger than 100 km expected
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Quaoar
Finding a needle in a haystack
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Wednesday, November 2, 2011
Meteoroids
Small (µm – mm sized) dust grains throughout
the solar system
Wednesday, November 2, 2011
Meteoroids
Small (µm – mm sized) dust grains throughout
the solar system
If they collide with Earth, they evaporate in the
atmosphere.
Wednesday, November 2, 2011
Meteoroids
Small (µm – mm sized) dust grains throughout
the solar system
If they collide with Earth, they evaporate in the
atmosphere.
→ Visible as streaks of light: meteors.
Wednesday, November 2, 2011