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

• 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!

Nebulas

Planetary nebula remaining mineral particles and gas

after a star explodes

Butterfly nebula 3800 light years

away

Which elements are formed during

the normal evolution of a star?

Which are formed during a supernova

explosion?

NOVAS = exploding starsSUPERNOVAS = really big

exploding stars

The Solar System began with the collapseand condensation of a Planetary Nebula

• 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

Abundant carbon dioxide, methane, and ammonia. These are volatile gases most stable in outer region.

Approximately 5 bya, a swirling nebula began to

collapse inward under the pull of gravity

Planetesimal accretion

rocky particles and gases coalesce

into planets

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

MERCURY 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 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

Saturn

Uranus

Neptune

By volume, Jupiter is larger than all of the

other planets combined.

How many times larger is it (by volume) than

the Earth? Earth to the same scale

JUPITER 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

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 ?

Other Objects

Other objects in the Solar System include:

• Dwarf Planets

• Comets

• Asteroids

Comet exhibiting coma (tail)

What makes a comet’s tail?

Dwarf Planet

“an object in the Solar System that orbits the Sun and is not asatellite 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

Asteroids and Comets

Asteroids

• 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?

“Hadean Era”

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.

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:

Earth’s gravity captureda passing planetesimal

Double planet hypothesis

Earth and the Moon wereformed concurrently from alocal cloud of gas and dust

Fission hypothesis:

Centrifugal force associatedwith Earth’s spin caused a bulge of material to separate from Earth

Impact hypothesis:Earth suffered a massivecollision with a Mars-sizedobject ejecting parts ofEarth’s mantle and coreinto 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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