Unit 1.3: Our Solar System

1. Unit 1.3: Our Solar System

2. 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

3. 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

4. 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)

5. 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

6. 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)

8. 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

9. 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

10. 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

11. Comparing Inner and Outer Planets

12. 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

13. 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

15. 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…)

17. 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!

18. 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?

19. 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

20. 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

21. 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

22. 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?

23. 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

24. Warm-up answers for this unit: