CHAPTER 2: Solar System

Why are planets close to the Sun, such as Earth, rocky with thin atmospheres, while those far from the Sun, such as Jupiter, are gaseous with thick atmospheres? JUPITER vs. EARTH

Earth’s Origin Is Described by the Solar Nebula Hypothesis The Sun is a star at the centre of our Solar System -one of billions in the Milky Way Galaxy The Solar System formed approx-imately 4.6 bya The Sun and other objects originated from the collapse and rotation of a nebula “bya” means “billions of years ago” – another way to write that is Ga = giga-annum

Nebulas A Nebula is a cloud of gas and dust Planetary nebula remaining mineral particles and gas after a star explodes A Nebula is a cloud of gas and dust Stars release energy and build elements through nuclear fusion Stars “burn” their hydrogen becoming brighter Eventually, stars become Red Giants and explode! Which elements are formed during the normal evolution of a star? Which are formed during a supernova explosion? NOVAS = exploding stars SUPERNOVAS = really big exploding stars Butterfly nebula 3800 light years away

The Solar System began with the collapse and condensation of a Planetary Nebula Abundant carbon dioxide, methane, and ammonia. These are volatile gases most stable in outer region. Suggested tips to give students: Copernican heliocentrism is the name given to Nicolaus Copernicus’ theory (published in 1543) that the Sun was in the center of the Universe. Volatile gases = easily evaporated. The planetesimal hypothesis of Viktor Saranov, states that planets form out of dust grains that collide and stick to form larger and larger bodies. It is highly recommended to focus on the introduction to Section 2-2 for a more complete explanation. Rocky particles and metallic compounds formed solids in the inner region (Terrestrial Planets) Outer region (cooler) solids formed of hydrogen compounds, metals, and rocks (Gas Giants) Transition zone between the two regions is known informally as the “frost line” Nuclear fusion in core released Solar Wind and stopped contraction

Planetesimal accretion rocky particles and gases coalesce into planets Approximately 5 bya, a swirling nebula began to collapse inward under the pull of gravity

The Solar System consists of: 8 planets 5 dwarf planets numerous small solar system bodies 240 known satellites (moons) Countless particles and interplanetary gas molecules Earth, the Sun, and other objects in the Solar System originated at the same time from the same source and have evolved in varying ways since then. Why is Pluto no longer considered to be one of the main planets?

Our Sun: A Massive Hydrogen Bomb held together by gravity The solar core is site of nuclear fusion 4 H atoms are forced together to form 1 He, which has less mass Mass differential is expelled as energy (light and heat) The Sun is getting “lighter” (less mass) and hotter through time It has enough fuel to last another 4 to 5 billion years How much hotter is the sun now than it used to be 4 bya?

Terrestrial planets are small and rocky, with thin atmospheres MERCURY VENUS EARTH MARS Terrestrial planets are small and rocky, with thin atmospheres

Mercury Venus EARTH Mars Atmosphere: 42% O2, 28% Na, 22% H2, 6% He, 5% K Extreme daytime heat, extreme nighttime cold Venus Atmosphere: Carbon dioxide 96.5% CO2, 3.5% N2 Even hotter than Mercury due to high percentage of CO2 EARTH Atmosphere: 78.09% N2, 20.95% O2, 0.93% Ar, 0.39% CO2, variable H2O Hot, energy-providing core with surface cool enough for liquid H2O Mars Atmosphere: 95.3% CO2, 2.7% N2, 1.6% Ar, 0.13% O2 Most Earthlike with dry river channels indicating water Suggested tips to give students: Geologists worldwide are analyzing photographs taken by the Mars Rover to discern the characteristic features of sedimentary rocks – see Chapter 8 and http://marsrover.nasa.gov/home/ Initially the Earth had an atmosphere similar to those of Venus and Mars. In what way has it changed and why?

Gas Giants are massive planets with thick atmospheres. Jupiter Neptune By volume, Jupiter is larger than all of the other planets combined. How many times larger is it (by volume) than the Earth? Uranus Saturn Earth to the same scale

JUPITER SATURN URANUS NEPTUNE Atmosphere: 89.8% H2, 10.2% He Third-brightest object in the night sky after the Moon and Venus SATURN Saturn’s Atmosphere: 96.3% H2, 3.25% He Oblate due to a high rate of rotation URANUS Atmosphere: 82.5% H2, 15.2% He, 2.3% CH4 The only planet that does not rotate perpendicular to the ecliptic NEPTUNE Neptune’s Atmosphere: 80% H2, 19% He, 1.5% CH4 Inner two-thirds are likely composed of a mixture of molten rock, water, liquid ammonia, and methane Suggested tips to give students: Geologists worldwide are analyzing photographs taken by the Mars Rover to discern the characteristic features of sedimentary rocks – see Chapter 8 and http://marsrover.nasa.gov/home/ In reference to Uranus, what do we mean when we say “does not rotate perpendicular to the ecliptic”, and why might this be the case ?

What makes a comet’s tail? Other Objects Other objects in the Solar System include: Dwarf Planets Comets Asteroids What makes a comet’s tail? Comet exhibiting coma (tail)

Dwarf Planet “an object in the Solar System that orbits the Sun and is not a satellite of another planet or other celestial body. It must be spherical (or nearly so) in shape.”

The Five OFFICIALLY RECOGNIZED Dwarf Planets HAUMEA, MAKEMAKE and PLUTO (with its moon, Charon) located in the Kuiper Belt Pluto’s Atmosphere: 98% N2, < 1% H2O, < 1% CH4, < 1% CO Pluto and Charon considered a “double-dwarf”. ERIS located in the scattered disk region CERES a large asteroid located in the asteroid belt

Why are asteroids and comets not spherical like the planets? Rocky, metallic planetesimals. Comets Icy (water ice and other frozen liquids or gases) planetesimals. Two views of Eros 10 km Why are asteroids and comets not spherical like the planets?

Can you label it?

EARTH’S interior was hot to begin with (due to collisions) but it got even hotter because of nuclear fission An atmosphere was created by volcanic outgassing and delivery of gases and water by ice-covered comets. “Hadean Era” Suggested tips to give students: Hadean derives from Hades, Greek for ”Underworld” or “Hell”, referring to the conditions on Earth at the time. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks.

Earth’s Geomagnetic Field The magnetic field is created by motion of the Earth’s liquid outer core, and blown into a streamlined shape by the Solar wind

WHAT ABOUT THE ORIGIN OF THE MOON? Capture hypothesis: Fission hypothesis: Earth’s gravity captured a passing planetesimal Centrifugal force associated with Earth’s spin caused a bulge of material to separate from Earth Double planet hypothesis Impact hypothesis: Earth and the Moon were formed concurrently from a local cloud of gas and dust Earth suffered a massive collision with a Mars-sized object ejecting parts of Earth’s mantle and core into orbit

Impact Hypothesis Most widely accepted hypothesis of moon formation What are some of the characteristics of the Earth and Moon that support this hypothesis?

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