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Unit 1.3: Our Solar System. I. Formation of the Solar System. Nebular hypothesis : bodies of solar system condensed from enormous cloud of interstellar dust as follows: As nebula begins to contract, spins faster and flattens into a disk shape Evidence: planar orbits

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i formation of the solar system
I. Formation of the Solar System
  • Nebular hypothesis: bodies of solar system condensed from enormous cloud of interstellar dust as follows:
    • As nebula begins to contract, spins faster and flattens into a disk shape
      • Evidence: planar orbits
    • Most material pulled to center  becomes protosun
    • Temperature drops, allows iron/nickel to solidify

Accretion of these solid particles  forms “planetesimals”

    • Accretion: clumping of debris to make larger planetary bodies (planetesimals)
    • Gravity of planetesimals allows further accumulation to become protoplanets
  • As protoplanets accumulate debris in solar system, helps to “clear out” solar system
    • Now, solar radiation can heat protoplanets
  • Heat causes gases to vaporize from inner planets, carried away by solar winds
the sun 99 85 of mass of solar system
The Sun: ~99.85% of mass of solar system
  • The Sun’s Interior
    • Core: undergoing nuclear fusion H  He
    • Radiative Zone: surrounds the core
      • Energy “radiates” away from core as electromagnetic waves
    • Convective Zone: convection gives rise to sunspots:
      • Convection is the transfer of energy by moving matter
      • As hot gases rise to surface, they expand and cool (light spots)
      • But, as they cool, they condense and sink back into Sun (dark spots)
the sun s atmosphere
The Sun’s Atmosphere
  • Photosphere – “sphere of light”:
    • Energy is given off in the form of visible light
  • Chromosphere: “sphere of color”
    • Thin layer of gases
    • Appears as thin, red rim around the Sun b/c of hydrogen cooling
    • Solar eruptions:
      • Spicules: small flares
      • Prominences: large flares that erupt due to interaction with magnetic fields
      • Solar flares: largest eruptions of energy

Corona – “crown”

    • Outermost portion of solar atmosphere
    • Solar wind: ionized gases (plasma) that escape the Sun’s gravity
      • Mostly lost to space
      • But if it reaches Earth, interacts with our magnetic field to create auroras (Northern and Southern lights)
iii planet formation
III. Planet Formation
  • As remaining dust condenses to become a planet, chemical differentiation occurs:
    • Denser, heavier elements (nickel and iron) sink towards center of planet
    • Lighter elements (silicon, oxygen, hydrogen) move towards surface of planet
    • Gases escape unless a planet has enough surface gravity to hold them in an atmosphere
      • Escape velocity: speed an object must reach to escape the gravitational pull of a planet
        • 11km/sec for Earth
        • Higher speed for Jovian planets b/c greater surface gravity
b inner planets mercury venus earth mars
B. Inner Planets: Mercury, Venus, Earth, Mars
  • Terrestrial planets: ‘terra-’ = Earth
  • Between Sun and asteroid belt
  • Rocky planets, metallic core
    • Dense b/c gravity pulls heavier elements closer to Sun
  • Thin to no atmosphere
    • Because they are closer to Sun, they are warmer, so fewer gases, ices
  • Smaller in diameter
    • Too warm to retain gases = little to no atmosphere = smaller planets
  • Few to no satellites: 0-2 moons
    • Smaller planets = less gravity = fewer moons
c outer planets jupiter saturn uranus neptune
C. Outer Planets: Jupiter, Saturn, Uranus, Neptune
  • “Jovian” planets: ‘jove-’ = Jupiter-like
  • Beyond asteroid belt
  • Gaseous planets, some metals in core
    • Less dense b/c greater amount of light gases than inner planets
  • Thick atmosphere
    • Farther from Sun, colder, able to retain gases
    • Lower temps = less energy, lighter gases cannot “escape”
  • Larger in diameter
    • Primarily because of thicker atmospheres
  • Many satellites: 8-21 moons
    • Larger planets = more gravity, can “hold” more satellites

Dwarf Planets: (beyond Neptune)

    • Orbit the Sun:
      • If they orbited another planet, called a moon of that planet
    • Spherical in shape:
      • Gravity ‘pulls’ them into “spheres”
      • If irregular in shape, then asteroids, not planets
    • Not large enough to “clear” their orbit
      • Larger planets accrete smaller bodies or fling them out of their orbit - dwarf planets cannot
    • Ex: Pluto, Ceres, Eris,

Haumea, Makemake

iv the moon
IV. The Moon
  • Giant-impact hypothesis:
    • During formation of planets, large body impacted Earth, liquefied surface and ejected crustal and mantle rock
    • Debris entered orbit around Earth, coalesced into moon
  • Supporting evidence:
    • Density of moon is similar to density of material in Earth’s mantle, but not Earth’s core
      • Small iron core in Moon
c lunar surface
C. Lunar Surface
  • Craters: produced by impact of meteoroids
    • No atmosphere = no friction to slow down impact
    • Meteoroid hits, compresses rock
    • Compressed rock rebounds, ejecting surface material from crater
    • Ejecta builds rim of crater
    • Heat of impact melts lunar rock:
      • Astronauts brought back glass beads made in this way
    • No change in shape b/c no processes of erosion (wind, water, etc…)

Highlands: mountain ranges due to tectonic processes

  • Maria: (L. mare = ‘sea’) “Seas” of basaltic lava that bled out when asteroids punctured surface
  • Regolith: soil-like layer of lunar dust generated from erosion by meteors
    • ~10 ft thick!
v small solar system bodies
V. Small Solar System Bodies
  • Asteroids: small, rocky bodies
    • Microplanets: grains of “sand” up to 1000 km across
    • Most found in asteroid belt, between Mars and Jupiter
      • Others originate in Kuiper Belt just beyond Uranus
    • Fragments of broken planet?
      • Not enough mass
    • Or several larger asteroidal bodies that collided, making smaller asteroids?

Comets: “icy dirtballs”

    • Originate from Kuiper Belt or from Oort Cloud
    • Rocky, metallic materials held together by frozen gases: H2O, methane, ammonia, CO2, and CO
    • Parts of a comet:
      • Coma: glowing nucleus, the head of the comet
      • Tail: as it approaches the Sun, gases vaporize, begin trailing the head

Orbit of a comet:

    • Tail always points away from Sun b/c:
      • Radiation pressure from Sun pushes dust particles away from coma; forms one tail
      • Solar winds move ionized gases, esp. carbon monoxide; forms a second tail
    • As comet moves away from Sun, gases/dust recondense
    • Every revolution, size decreases b/c loses mass

Meteors: “shooting star”

    • In space, it’s called a meteor, but as it burns up in Earth’s atmosphere, it’s called a meteoroid
    • Meteorite: remains of a meteoroid, found on Earth
    • Meteor shower: a large # (60+) of meteoroids traveling in same direction, at nearly same speed of Earth

Meteors are classified according to composition:

    • Irons: mostly iron, and 5-20% nickel
    • Stony: silicate materials, other minerals
    • Stony-irons: mixtures
    • Carbonaceous chondrites: contain amino acids, other organic compounds – life from outer space?

Impact of meteors on Earth:

    • Moon-like craters
    • Meteor Crater, Arizona:
      • ¾ mi across, 560 ft. deep
    • Extinction events?
      • Iridium – common in meteors – found in a layer of Earth that corresponds to time when dinosaurs are believed to have gone extinct
    • Why are there so few craters on the Earth, and so many on the moon?
      • Erosion, weathering has actively “recycled” craters back into Earth’s crust
  • Age of meteorites confirms age of Earth @ 4.5 billion years old