Ou r

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Ou r So l a r
System
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29.1 Overview of Our Solar System

• Objectives
• Describe early models of our solar system
• Examine the modern, heliocentric model of our
  solar system
• Relate gravity to the motions of celestial
  bodies.
• Vocabulary
• Retrograde motion Eccentricity
• Astronomical Unit Aphelion
• Perihelion

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Planets Currently Visible
Mercury very low in morning sky. Nearly
impossible to see. Venus -- in the evening sky,
just too low in the West-northwest to see. It
doesn't improve much until the Fall. Mars in
the East-southeast in Aquarius, rising several
hours before the Sun. While hardly stunning right
now, it does stand out in an otherwise dull part
of the heavens. Jupiter only planet easily
visible through the evening. In Virgo, it is the
brightest object in the sky other than the Moon
and Venus (and Venus hardly counts this month!)
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Early Ideas

• When you look up and notice that the sun has
  moved from east to west over the course of a few
  hours, doesnt it seem as though Earth is
  standing still and the sun is moving across the
  sky?
• This perception that the Earth is stationary
  was the basis of ancient Greek theories that
  prevailed for over two thousand years.

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Early Ideas

• Ancient astronomers (as long as 6000 years ago)
  noticed that the stars appeared to move across
  the sky, but they did not move in relation to
  each other.
• To explain this, the astronomers envisioned the
  stars as holes in a solid celestial sphere that
  surrounded Earth. Beyond the sphere, they
  imagined a source of intense light that shone
  through the holes. They concluded that the stars
  moved around Earth as the sphere rotated.

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Early Ideas

• How could early astronomers recognize the
  difference between a planet and a star?

Planets slowly change position each night with
respect to the stars.

• What assumption did early astronomers make about
  how the Earth, Sun and planets move?

Geocentric Geo means Earth, centric means
centered, so geocentric is Earth centered.
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Early Ideas
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Early Ideas

• Lights that wandered across the sky were
  correctly identified as planets.
• Early astronomers noticed that most of the time
  the planets moved eastward in front of the
  background of constellations. Periodically, the
  planets stopped moving eastward and moved
  westward for a few weeks, then resumed their
  eastward paths.
• The pattern of apparent backward motion is called
  retrograde motion.

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Retrograde motion

• What direction does it look like a car that you
  are passing is going in relation to the
  background?

Earth moves faster than Mars, causing it to
appear like it is moving backwards.
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Models

• The geocentric model couldnt explain retrograde
  motion.

• Who suggested that the Sun was the center of the
  universe?

Nicolaus Copernicus

• What is the sun-centered model called?

Heliocentric model

• This model could explain the observed retrograde
  motion.
• Was it accepted quickly?

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Keplers First Law

• The Sun is always located at one focus point for
  each planet.

• The average distance between the Sun and the
  planet would be equal to half the major axis.
• This is called the semi-major axis.
• For the Sun and Earth, the semi-major axis is
  1.496 X108 km, or 1 AU.

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Keplers Second Law

• Kepler also discovered that an imaginary line
  drawn from a planet to the Sun sweeps out equal
  amount of area in equal amounts of time.

Planets move fastest when closest to the Sun.
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Keplers Third Law

• Kepler determined the mathematical relationship
  between the size of a planets ellipse and the
  time it takes to complete one orbit (orbital
  period).

P2 a3
P is measured in Earth years
a is measured in Astronomical Units.
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Galileos Discoveries

• Galileo was the first person to observe the sky
  with a telescope.
• What did he discover about Jupiters moons?

They orbited Jupiter

• How did this help support Copernicus heliocentric
  model?

It showed that not all celestial bodies orbit the
Earth, thus the Earth wasnt necessarily the
center of the solar system.
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Newtons Contributions

• Newtons contribution to modern science was
  enormous.
• He invented calculus, studied the composition of
  light, and established classical physics.
• He came up with three laws of motion and the law
  of gravitation.

Isaac Newton
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Newtons Contributions

• Isaac Newton observed the Moons motion, the
  orbit of the planets and the acceleration of
  falling objects on Earth.
• He discovered that any two objects attract each
  other with a force that depends on their masses
  and the distance between them.

Law of Universal Gravitation
Mass of objects.
Distance between objects.
G 6.67 X 10-11 m3/kg/sec
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Newtons Contributions

• Consider the Moon and the Earth if the mass of
  the moon were doubled, would the attractive force
  increase or decrease?
• How would the force change if the Moon was twice
  as far away as it is?

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Newtons Contributions

• Newton determined that each planet orbits a point
  between it and the Sun, called the center of
  mass.
• The center of mass is the balance point between
  the two orbiting bodies.
• The center of mass will be closest to the body
  with the larger mass. In our case, this would be
  the _____.
• In fact, since the Sun is so massive compared to
  the Earth and other planets, the center of mass
  is just above the surface, or within it.

Sun
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29.1 Overview of our Solar System -- Review

• Name and describe the model of the solar system
  that early astronomers proposed.
• What were some problems with the early model?
• What is retrograde motion?
• Name and describe the current model of the solar
  system.
• What 3 things did Kepler discover?
• What is the force of attraction between two
  objects depend on?
• What is the center of mass?

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29.2 The Terrestrial Planets

• Objectives
• Describe the properties of terrestrial planets.
• Compare Earth with the other terrestrial planets.
• Vocabulary
• Terrestrial planet
• Gas giant planet
• Precession

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29.3 The Gas Giant Planets

• Objectives
• Describe the properties of the gas giant planets
• Identify the unique nature of the planet Pluto
• Vocabulary
• Liquid metallic hydrogen
• Belt
• Zone

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Solar System
Inner planets terrestrial planets
Outer planets Jovian Planets

• Jupiter-like
• Beyond asteroid belt
• Jupiter, Saturn, Uranus and Neptune are larger
  than Earth gaseous
• Outer layer mostly H2 compressed H2 liquid near
  center cold surface
• Less dense than Earth
• Ring systems

• Earth-like
• Rocky crusts
• Dense mantle layers
• Very dense cores
• Mercury, Venus, Earth and Mars

Pluto is exception -- not dense enough to be a
terrestrial planet not large enough to be a
Jovian planet
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Earth
General Information
Atmosphere

• Distance from sun nearly circular orbit allows
  water to exist in all three states
• Water supports life
• Ground and surface water present
• Precesses about axis due to sideways pull of Moon
  Earth gravity

• Moderately dense atmosphere
• 78 N2 and 21 O2
• Mild greenhouse effect

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Earth
Surface
Interior

• Rocky crust
• Erosion occurs ? little remaining evidence of
  crater impacts
• System of crustal plates tectonic activity

• Rigid outer crusts ? continental oceanic
• Mantle ? upper is rigid lower is partially
  molten
• Core ?Outer liquid and solid inner part composed
  of iron and nickel
• Magnetic field

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Mercury
General information
Atmosphere

• Essentially none mostly Oxygen and Sodium
• Temperature range ? 173oC to 427oC which is
  largest range for all planets

• Closest to sun no moons
• One-third the size of Earth
• Slow rotation of 1407.6 hours
• 3 days (3 rotations) in 2 years (orbits)

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Mercury
Surface
Interior

• Like Moon ? covered with craters and plains,
  maybe formed from lava flows like maria on Moon
• Shorter ejecta lower crater peaks walls since
  the gravity is higher than moon
• System of cliffs, called scarps which developed
  when crust shrank fractured.

• High density suggests Ni-Fe core
• Weak magnetic field (1 of Earths, suggests
  molten interior
• Interior is like the Earth if the Earths crust
  and mantle were removed.
• Perhaps Mercury lost crust and mantle in
  collision?

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Venus
General information
Atmosphere

• No moons
• Brightest planet close to Earth and albedo of
  0.73
• Surface observation by radio waves due to thick
  surface clouds
• One day 243 Earth days. Spins opposite most
  planets retrograde rotation
• Most similar to Earth in diameter, mass and
  density.

• Atmosphere has pressure 92 times that on Earth
• Mostly CO2 and N2
• Thick clouds made of Sulfuric acid
• High CO2 ? efficient greenhouse effect ? hottest
  planet ? Average 464oC hot enough to melt lead!

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Venus
Surface
Interior

• Smoothed by lava flow
• Only a few impact craters
• Little evidence of current tectonic activity
• No well-defined system of crustal plates

• Size and density similar to Earth, so believe
  internal structure is, but no data to prove
• Theorized that Venus has liquid metal core
  extending halfway to surface
• No measured magnetic field

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Mars
General Information
Atmosphere

• Fourth planet from sun outermost of terrestrial
  planets
• Red surface color from high iron content
• Smaller and less dense than Earth
• Two irregularly shaped moons Phobus and Deimos
• Explored by telescopes probes

• Similar to Venus, mostly CO2, but much lower
  pressure and density
• Doesnt have strong greenhouse effect
• Thin atmosphere
• Turbulent, constant winds
• Believe it was once warmer, thicker and richer in
  CO2 to allow water

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Mars
Surface
Surface

• Southern Hemisphere ? heavily cratered like
  Moons highlands
• Northern Hemisphere ? plains from lava flows with
  few craters
• 4 large volcanoes in Northern hemisphere ?
  Olympus Mons is largest mountain in solar system
  ? base would cover Colorado 3X as high as Everest

• Dried river lake beds, outflow and runoff
  channels suggest water once present
• Small amount of ice at poles
• Polar caps of CO2 grow and shrink with season.
  Water ice beneath in Northern Hemisphere.

Interior

• Unsure, but believe to be

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Mars
Interior

• Unsure, but believe to be Fe and Ni core possibly
  with some sulfur
• Extends out between 1200-2400 km
• No magnetic field believe solid core
• Mantle above core
• No evidence of current tectonic activity or
  plates.

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Jupiter
General Information
General Information

• Largest planet 5th from Sun
• Diameter is 11X that of earth and only 10X
  smaller than Suns
• Jupiters mass accounts for 70 of mass in our
  solar system
• Bright, albedo is 0.343
• Banded appearance from atmosphere

• 4 major satellites and 12 smaller ones. 61 total
  moons
• Volcanic activity on Io, largest moon.
• Voyager 1 2 discovered several new satellites
  and a thin dim ring around Jupiter.

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Jupiter
Atmosphere
Interior

• Low density for huge size because its made of
  lightweight elements
• Atmosphere is gaseous and liquid H2 He
• Spins on axis in 10 hours
• Rapid rotation distorts shape, causes fast cloud
  flow Belts ? low, warm, dark-colored clouds
  Zones ? high, cool, light colored clouds

• May have Earth sized solid core of heavier
  elements
• Liquid metallic hydrogen below the liquid
  hydrogen special form only exists in high
  pressure.
• Electric currents flow in liquid metal creating
  magnetic field

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Jupiter
Moons and Rings
Moons and Rings

• Four largest moons Io, Europa, Ganymede
  Callisto
• All larger than Pluto 3 larger than Earths
  moon
• Rock ice mixtures
• Io and Europa have less ice since been squeezed
  and heated by Jupiter gravitational force.

• Io almost completely molten inside undergoes
  constant volcanic eruptions.
• Gravitational heating melted Europas ice may
  have subsurface liquid water
• Rings discovered by Voyager 1

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Saturn
General Information
Atmosphere

• Second largest in solar system 6th from Sun
• Being explored by Cassini mission new moon
  discovered on May 10th.

• Not quite as large as Jupiter average density is
  lower than that of water
• Hydrogen and helium atmosphere, ammonia ice near
  top of clouds
• Rotates rapidly and has flowing belts and zones

Interior

• Fluid internal structure with a small, solid core
• Magnetic field 1000 X Earths.
• Magnetic field aligned with rotational axis.

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Saturn
Moons and Rings
Moons and Rings

• Large, bright ring system
• Rock and ice particles from microscopic to
  house-size
• Rings are thin and confined to equatorial plan
  gravity prevents combining.
• Rings may be debris from moon destroyed by
  collision with asteroid or ripped apart by gravity

• Seven major rings made up of narrower rings
  called ringlets and open gaps caused by
  gravitational effects of many moons.
• 18 known satellites, including Titan, the
  largest. Titan could be planet orbiting another
  planet
• Titan has methane atmosphere

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Uranus
General Information
Atmosphere

• Seventh planet from Sun
• Discovered accidentally in 1781 through telescope
• 4 times as large and 15 times as dense as Earth

• Composed of helium, hydrogen and methane
  atmosphere
• Methane reflects blue light, giving bluish
  appearance.
• Very few clouds almost same brightness and color
  as surrounding atmosphere, so difficult to
  detect.
• No belts or zones

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Uranus
Internal Structure
Moons Rings

• Liquid with a small, solid core
• Strong magnetic field
• Rotational axis tipped almost to orbital plane
  maybe knocked sideways in a collision

• 21 known moons and the rings orbit in equatorial
  plane more moons being discovered.
• Rings are very dark so werent discovered until
  the brightness of a star behind the rings
  decreased when Uranus moved in orbit

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Neptune
General Information
Atmosphere

• Existence predicted before discovery based on
  small changes in Uranuss motion and Newtons law
• Slightly smaller and denser than Uranus
• Four times as large as Earth
• Most information from Voyager 2

• Composed of helium, hydrogen and methane
  atmosphere
• Like Uranus, methane reflects blue light, giving
  bluish appearance.
• Distinctive clouds has belts or zones
• Great Dark spot was a persistent storm that ended
  in 1994

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Neptune
Moons and Rings
Moons and Rings

• Eight moons, largest is Tritan
• Tritan has retrograde orbit ? it orbits backwards
• Tritan has thin atmosphere and nitrogen geysers
  from nitrogen gas below surface in south polar
  ice cap that expands and erupts when heated by sun

• Six rings composed of microscopic-sized dust
  particles.
• Some particles in outermost ring clump together
  to give brighter particles

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Pluto
General information
General information

• 9th planet, discovered in 1930 smaller than
  Earths moon
• Very different from others
• Solid surface, but low density and small size
  keep it from being classified as terrestrial.
• Probably half rock and half ice
• Similar to gas giant moons escaped from Neptune?

• Atmosphere is methane and nitrogen
• Very eccentric orbit, sometimes inside of Neptune
• Rotational axis tipped below equatorial plane
• Moon called Charon orbits equatorial plane in
  synchronous rotation.
• Sometimes called double planet.

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Belts and Zones

• Jupiter rotates rapidly, which distorts the shape
  of the planet.
• It also causes the clouds to flow rapidly as
  well.
• Belts are low, warm, dark-colored clouds that
  sink.
• Zones are high, cool, light-colored clouds that
  rise.
• Jupiters Red Spot is a storm that has been
  rotating around Jupiter for more than 300 years.

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Current Missions MESSENGER

• Mission to Mercury
• Why is Mercury so dense?
• What is the geologic history of Mercury?
• What is the structure of Mercurys core?
• Water at the poles?
• What is the nature of Mercurys magnetic field?

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Current Missions Mars Rovers

• Spirit and Opportunity are currently on the
  surface of Mars.

Mars Rover
Utopian Plain
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Mars Rovers
360-degree panorama picture of Mars surface from
a Rover.
Twin Peaks
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Current Missions Cassini - Huygens
The Cassini orbiter will orbit Saturn and its
moons for four years.
Cassini orbiter
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Current Missions Cassini - Huygens
On December 25, 2004 the Huygens probe will dive
into the atmosphere of Titan and land on its
surface. The probe will study Titans atmosphere
and collect data and images on the surface.
Huygens probe separating from Cassini
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29.4 Formation of Our Solar System

• Objectives
• Summarize the properties of the solar system that
  support the theory of the solar systems
  formation
• Describe how the planets formed from a disk
  surrounding the Sun
• Explore remnants of solar system formation
• Vocabulary
• Planetesimal Comet
• Asteroid Coma
• Meteoroid Nucleus
• Meteor Meteor Shower
• Meteroite

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Collapsing Interstellar Cloud

• Stars and planets form from clouds of dust and
  gas, called interstellar clouds.
• These exist in the space between stars and are
  mostly hydrogen and helium

• The dust in the clouds can block light making
  them look dark, or reflect it and partially
  illuminate the cloud.
• They can also be heated by stars and glow.

Light dark blotches.
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Collapsing Interstellar Cloud

• Intersteller clouds can start to condense as a
  result of gravitational forces and become
  concentrated enough to form a star and possibly
  planets.
• Scientists hypothesize that our solar system
  began this way.
• A cloud of gas and dust in space was disturbed,
  maybe by the explosion of a nearby star.
• This explosion made waves in space which squeezed
  the cloud of gas and dust and made the cloud
  start to collapse
• As gravity pulled the gas and dust closer
  together, the cloud began to spin.

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Sun and Planet Formation

• The cloud grew hotter and denser in the center,
  with a disk of gas and dust surrounding it that
  was hot in the center but cool at the edges.
• As the disk got thinner and thinner, particles
  began to stick together and form clumps. Some
  clumps got bigger, as particles and small clumps
  stuck to them, eventually forming planets or
  moons.

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Sun and Planet Formation

• Eventually the rate of condensation slowed
• Area closest to Sun were still warm, while areas
  on outer edge of disk were cold, thus different
  elements and compounds condensed, depending on
  distance from Sun.
• See figure 29-28 in text.
• The tiny grains of condensed material started to
  accumulate and merge into larger bodies called
  planetesimals.
• Some grains collided and stuck together
• Gas particles collided on surfaces of grains

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Sun and Planet Formation

• Continued growth occurred through collisions and
  mergers of planetesimals. Collisions were
  violent and sometimes destroyed planetesimals.
• Jupiter was the first planet to develop in outer
  solar system.
• As it grew in size, its gravity attracted other
  gas, dust and planetesimals, making it bigger.
• Saturn and Neptune did the same, but couldnt
  grow as big since Jupiter had captured the
  particles.
• As each gas giant grew, a disk formed in
  equatorial region.
• In the disk, matter coalesced into satellites.

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Sun and Planet Formation

• Near the Sun, in the inner part of main disk,
  planets also formed from merging of
  planetesimals.
• Composed of refractory elements (high melting
  point elements) so inner planets are rocky and
  dense
• Suns gravity also believed to have used up gas
  in inner locations, thus inner planets dont have
  many satellites.
• Most debris crashed into planets or exited solar
  system, but an asteroid belt remains between
  Jupiter and Mars, because Jupiters gravity
  prevented them from exiting.

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Sun and Planet Formation
Regions in the Orion Nebula (1500 light years
from Earth) where solar systems appear to be
forming.
http//csep10.phys.utk.edu/astr161/lect/solarsys/f
orming.html
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Asteroids

• Leftovers from formation of Solar System
• Range in size from few kilometers (3-5 miles) to
  1000 km (650 miles)
• Not pieces of planets that were destroyed as once
  thought
• Total mass of all asteroids only about 0.08
  that of Earth.
• When collide, break into fragments
• This or any interplanetary material that falls
  towards Earth and enters atmosphere is called a
  meteoroid. It burns up in Earths atmosphere,
  producing bright streak of light called meteor.
• If doesnt burn completely, collides with ground
  as meteorite.

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Comets

• Leftovers from formation of Solar System
• Small icy bodies that have highly eccentric
  orbits around Sun are called comets.
• Made of ice and rock
• Range from 1 km (0.6 mile) to 10 km (6.2 miles)
• Two clusters or clouds of comets
• Kuiper Belt close to Pluto and between 30 and
  50 AU from Sun.
• Oort Belt More than 100,000 AU from Sun
• Occasionally, gravity from another object will
  throw one of these into inner solar system.

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Orbits of Comets

• Highly eccentric orbits
• Some are far beyond the aphelion of Pluto, while
  others come close to the Sun at perihelion.
• When a comet comes within 3AU of Sun, it begins
  to evaporate, become brighter and form a head and
  one or more tails.

Halle Bopp comet
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Orbits of Comets
Head of comet is extended body of glowing gas
called coma.

• Inside coma is the small, solid core, or nucleus.
• When the nucleus is heated, it releases gases and
  dust particles.
• The tail is always pushed away from the Sun, by
  particles and ions coming from sun and the
  pressure of Suns radiation.

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Periodic Comets

• Comets that orbit in the inner solar system are
  called periodic comets.
• Halleys comet has a period of 76 years. It will
  appear again in 2061.
• Each time a comet comes near Sun, the Sun
  vaporizes some of ice and comet gets smaller.
  Eventually it breaks apart.
• If a cometary orbit enters the Earths
  atmosphere, we see a meteor shower as particles
  burn up.
• Most meteors are are caused by comets.
• Most meteorites are fragments of asteroids.

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