Solar System. Astronomy 1-1 Lecture 07-1

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Solar System

Consists of

Sun

8 Planets

Mercury, Venus, Earth, Mars,

Jupiter, Saturn

,

Uranus

,

Neptune

, and

(Pluto)

165 Moons

Asteroid Belt between Mars and Jupiter

Comets

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Measuring the Planets

Orbital Period -

Can be observed

Distance from Sun -

Known by Kepler’s laws

Radius -

Known from angular size and distance

Masses

- From Newton’s laws

Rotation Period

- From observations

Density

- Can be calculated knowing radius and

mass

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Overall Layout of the Solar System

All orbits but

Mercury’s are close to

same

plane

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Overall Layout of the Solar System

Because the planet’s

orbits are close to being

in a plane, it is possible

for them to appear in a

straight line as viewed

from Earth

This photograph was

taken in April 2002

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Major Planetary Points

Mercury Scorched, heavily cratered

Venus Dense, Corrosive cloud cover

Earth Life Supporting

Mars Great dust storms

Jupiter Great Red Spot

Saturn Spectacular ring systems

Uranus Tilted on its side

Neptune Interesting Moon

(Pluto Highly eccentric orbit)

With the exception of Pluto, all the planets are effectively in the equatorial plane of the Sun

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Planetary Motions

All the planets are moving

counterclockwise

around the Sun, when viewed from the Solar

North Pole

With the exception of Venus and Uranus, all the

planets, are rotating counterclockwise about

their own rotation axes

Venus is rotating clockwise about its own axis Uranus' rotation axis is in ecliptic plane

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Statistical Data

The planets can be divided into two groups:

The Terrestrials

Mercury, Venus, Earth, and Mars

These have densities > 3.9 gm/cm3

This is a density consistent with that of rock

The Gas Giants

Jupiter, Saturn, Uranus, and Neptune

These have densities < 2.0 gm/cm3

This is a density consistent with that of ices

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Comparison of Terrestrial and

Jovian Planets

Terrestrial

Close to the Sun

Closely Spaced Orbits Small Masses Small Radii Predominantly Rocky Solid Surface High Density Slow Rotation

Weak Magnetic Fields Few Moons

No Rings

Jovian

Far from Sun

Widely Spaced Orbits Large Masses Large Radii Predominantly Gaseous No Solid Surface Low Density Fast Rotation

Strong Magnetic Fields Many Moons

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Differences Among the Terrestrial

Planets

All have atmospheres, but they are very different

Surface conditions vary as well

Only Earth has oxygen in its atmosphere and

liquid water on its surface

Earth and Mars spin at about the same rate;

Mercury is much slower, Venus is slow and

retrograde

Only Earth and Mars have moons

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Chemical Composition

Terrestrial Planets

Rocks and Metals

Inner Asteroids

Rocks and Metals

Outer Asteroids

Rocks, Metals, and Ices

Jovian Planets

Mostly Gas with Rock, Metal and Ice cores

Jovian Satellites

Pluto

Comets

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Solar System Formation

Nebular Hypothesis

Solar system formed from a condensing cloud of gas and dust which collapsed under gravitational forces

Condensation of smaller particles into larger

particles and then objects called planetesimals

The process of gathering up material is called accretion.

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Planetary Formation

Nebular Hypothesis

In inner region of disc temperatures high enough to drive away the lighter elements such as hydrogen and

helium, leaving behind the heavier elements.

Planetesimals collide at small relative velocities and merge forming even larger objects. These objects became

spherical in shape as this is the most stable.

Kinetic and potential energy are converted into heat energy which allows material to become partially

molten allowing the heavier elements to sink inwards. This process of the heavier elements sinking inwards is called differentiation.

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Solar System Formation

The observation of disks surrounding newly formed

stars supports this theory

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Heat Sources for a Planet

The conversion of kinetic energy of the planetesimals into heat energy is known as accretionary heating

As the heavier elements sink into the core region potential energy is converted into heat. This heat is from core

formation

As the radioactive elements decay additional heat is released

This is known as radiogenic heating

The interaction of two orbiting bodies will also cause tidal bulges. This stretching and contracting of the planetary mass yields heat energy

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Effects of Heating

Internal heating keeps some planets like the

Earth warm on the inside

Warm enough to have the internal material

molten or plasticized

The material on the surface, the crust, is solidified

This crust lies on a plasticized, molten layer

called the

mantle

The molten rock is called

magma when below

the

surface and

lava when above

the surface

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Crustal Layer

Often fragmented with the fragments being

called plates

These plates drift around on the mantle

This activity is called

plate tectonics

Volcanic activity often occurs along the

boundary between two plates

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Heat Transfer

Energy is transferred by three different means.

These are:

Convection

The transfer of energy by actual movement of material from one point to another

Conduction

The transfer of energy from one point to another by directly passing energy from atom to atom

Radiation

The transfer of energy by the emission of electromagnetic radiation

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Rock Forms

There are various forms of rocks that occur

throughout the solar system. These are:

Igneous

These are rocks that are formed when molten materials solidify

Sedimentary

These are rocks that have been formed from deposited layers of mud and clay

Metamorphic

These are rocks that have been altered by heat and pressure

On Earth there is a continuous cycling between

these three forms of rock

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Composition of Rocks

Rocks are made from various types of minerals Minerals are either single elements or molecules 90% of the rocks on Earth contain silicon

The most common silicon bearing rocks are: Quartz Feldspar Mica Hornblade

Other minerals that are in rocks are

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Planetary Atmospheres

With the exception of Mercury, all of the planets have atmospheres

There are several distinctions between the terrestrial planets and the gas giants:

1) The terrestrials have a distinct boundary between the atmosphere and the planet, whereas the gas giants do not have a clear boundary

2) The atmospheres that the terrestrial planets have are not their original atmospheres, while the

atmospheres on the gas giants are their original atmospheres

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When the Sun ignited, it threw off its outer tenuous layers as a wind, the T-Taurus wind. This wind blew off the original atmospheres of the terrestrials planets

While the terrestrial planets were partially molten, they outgassed through volcanic like processes

Since the initial outgassing, the atmospheres of Venus, Earth, and Mars have undergone changes

On Venus, the temperature of the atmosphere and also the surface has increased

On Earth, the original atmosphere contained very little, if any, oxygen

On Mars, the atmosphere has either escaped or been frozen out

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Atmospheric Circulation

The atmospheres on the planets are all in motion.

The reasons for this motion are:

Differential Heating

Equators receive more heat than polar regions. Atmosphere rises at equator and sinks at poles

Planetary Rotation

Causes currents to be deflected away from path towards the poles

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Tidal Forces

The gravitational interaction between the planets and their respective moons is not necessarily uniform

The resulting forces are known as a tidal forces. These forces act both on the planet and on the moon

This is seen on the Earth as the rising and lowering of the oceans - the tides

The greatest tides occur when the Sun, Earth, and Moon lie in a straight line

These are called spring tides

The tides are the least at first and last quarter moon when the Moon, Earth, and Sun form a right angle

These are called neap tides

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Tidal Effects

The Earth's tides are not aligned with the Earth-Moon direction

The tides point slightly ahead of the moon

This is because the Earth carries the oceans with it This "leading" bulge causes the Moon to accelerate

The Moon, because of its increasing velocity, moves into a higher orbit

The Moon's orbital radius is increasing at a rate of – 4 cm/year

The Earth's own rotational rate is also slowing down due to internal frictional forces

The day is becoming longer at a rate of - 0.002 sec/year

This process will stabilize when the Moon's rotation rate about the Earth matches the Earth's rotation rate