Unit 5 • Outline • A: Origin of Solar System • B: Planets • C: Moons
Big Bang 13.7 billion yrs ago
0 – 300,000 years: light elements (H2 and He) form (was 100% H2 & He; now 98%) • 300 ma: Universe continued expanding forming 1st stars (13.4 ba) and galaxies (Quasars = developing galaxy) • Stars produced heavier elements via fusion (Li – Fe) and exploding (super novas)
Solar Nebular Theory: • Deals with the creation of solar system 1. Swirling eddy cloud of dust and gas within the galaxy coalesces into a whirlpool.
2. As the whirlpool spins, it shrinks spinning faster finally into a spinning flat disc.
3. 90+ % of the mass concentrates at the centre to form an embryonic sun (proto-star) which emits light/heat and solar (hydrogen nuclei) wind
4. The Sun’s solar wind coupled with all the ionized gasses in the rotating disc caused a magnetic braking effect (Sun now rotates once/25 days) slowing disc down to moderate speeds. Ionized gasses Sun Lines of Magnetic force
5. Sun’s heat warmed inner disc so lighter elements could not condense so solar wind pushes most of these elements out to form gas giant planets. gaseous rocky frozen J E S M V E U N M P C Inner Planets Outer planets Hot Cold
Solar Nebular Theory Solar Nebular Theory
6. <10% of the mass accretes into larger and larger particles which eventually form planetesimals (60 – 100). As the planetesimals collided, they grew in size and mass (gravitational attraction), but fewer in number, to form the planets. • Large collisions among planetesimals resulted in: • Venus spinning backward very slowly • Uranus & Pluto spin on their side
Asteroids: left over planetesimals • Most between Mars and Jupiter (Jupiter’s gravity prevented formation of small planet).
Comets: formed near Uranus and Neptune; the immense gravitational pull of Saturn and Jupiter has created their highly elliptical orbits that range from the Sun to the Oort Cloud at the edge of the Solar System. Sun to Earth = 1 A.U. = dist’ Earth to Sun: 150 m km Sun to Pluto: 39 A.U. Sun to edge of Solar System: 35,000 A.U.
Oort Cloud Oort Cloud
Final Result: • All planets revolve around the Sun in same direction: CCW (Q.10, p.6) • Nearly all planets (‘cept Venus), moons orbit and spin/rotate in same direction: CCW • Nearly all axes of rotation are perpendicular to plane of revolution (Plane of the Ecliptic)
4. a) Terrestrial Planets: are small, rocky, high densities (4 – 5.5 gm/cm3) and metallic element (light elements blown…) b) Gaseous Planets: large, low densities (0.7– 1.7 gm/cm3 ) and mostly frozen compounds (cold, little solar wind) 5. Slow rotation of Sun (slowed by magnetic braking) 6. Asteroid belt between Mars and Jupiter (left over pieces of early Solar System)
B: Planets Terrestrial Two Types: and Jovian/Gas Giant Hand out data table on Planets
Terrestrial Planets • Metallic cores, silicate mantle-crust differentiated by volcanism and meteorite cratering • Atmosphere produced by volcanic outgassing • High densities: SG 4 – 5.5 • Slow rotators: 24+ hrs/day • Weak magnetic fields • Few, if any moons
Mercury 4880 km
1. Mercury • Smallest planet (slightly larger than our moon) • Closest to Sun (hot on sunny side; cold on shady side + long days: 1 M-day = 58 E-days) • Weak gravity and high temperatures caused loss of atmosphere to space • Radioactive heat expired long ago causing contraction of planet leading to normal faulting…heavy cratering over faults indicates cooling occurred long ago. (dating via principle of cross-cutting)
2. Venus (Earth’s sister/twin planet) because it’s the same size. • Shrouded in thick clouds of CO2 and N2. (90x Earth’s pressure) • Very hot (+450’C) with runaway greenhouse effect. • Active volcanism, folded mountains, faults, trenches indicate tectonic activity. • No magnetic field • Rotates backwards 1 V-day = 243 E-days
Venus 12100 km
Earth 12800 km
3. Earth • Active volcanism, folded mountains, faults, trenches indicates tectonic activity • Plate tectonics, oceans and weathering covers up meteorite impacts
4. Mars • ½ Earth’s diameter; twice Moon’s • Billions of years ago its volcanic outgassing provided ample CO2 and water for oceans. CO2 greenhouse effect warmed Mars so oceans flowed in great seasonal floods cutting immense canyons (and water depositional features). Volcanic activity slowed/ceased long ago (3.5 ba), CO2 atmosphere was lost to space, planet cooled and water froze.
Now frozen desert with wind storms and dunes. • N-hemisphere: large smooth plains, extensive volcanism (Olympus Mons: largest known volcano in Solar System), and few craters. • S-hemisphere: heavily cratered from meteorite bombardment (Hellas: 2000 km crater is largest known in Solar System).
Mars 6800 km