The Solar System

1
The Solar System
2
Observing the Solar System
3
Ancient Observations

• The ancient Greeks observed the sky and noticed
  that the moon, sun, and stars seemed to move in a
  circle around the Earth.
• It seemed that the Earth was not moving and
  everything in the heavens revolved around the
  Earth.
• As it turned out, it was very difficult to prove
  that the planets did not revolve around the Earth
  without leaving the planet.

4
Wandering Stars

• The Greeks also noticed that while the stars move
  across the sky, their patterns do not change.
• But five points of light did move among the
  stars.
• The Greeks called these objects planets, which
  means wandering star.
• They made careful observations of these planets,
  which we call Mercury, Venus, Mars, Jupiter, and
  Saturn.

5
Geocentric Theory

• Ancient Greeks such as Aristotle believed that
  the universe was perfect and finite, with the
  Earth at the exact center.
• This is the geocentric theory, which has the
  planets, moon, sun, and stars revolve around the
  Earth.

6
Ptolemy

• In 140 CE the Greek astronomer Ptolemy (85-165CE)
  revised the geocentric model to explain all the
  planetary motions.
• This was necessary as at times the planets seem
  to move backwards in the sky.
• His model had the planets move in little circles
  that also moved in bigger circles.
• This belief persisted for about 1400 years.

7
Ptolemaic Discrepancies

• Retrograde motion At times the planets would
  stop their movement in the sky, turn backwards
  for a few days, and then resume their forward
  progress.
• Jupiter's Moons Galileo first saw evidence that
  objects revolved around something besides the
  Earth.
• Galileo also saw that Mercury and Venus went
  through phases, just like our moon, but the outer
  planets did not.

8
Copernicus (1473-1543)

• In the early 1500s the polish astronomer
  Copernicus developed the heliocentric model.
• Helios means sun in Greek.
• He placed the sun at the center of the solar
  system and had the planets revolve around the
  sun.
• This was a very simple and elegant theory that
  explained all the planetary motions without the
  complexities of the Ptolemaic theory.
• Scientists prefer simple explanations over
  complex ones.
• Occam's Razor
• The simplest explanation is usually the best.

9
Retrograde Motion

• The apparent temporary backward motion of a
  planet.
• This is caused when a faster moving inner planet,
  say the Earth, bypasses a slower moving out
  planet, say Mars.

10
Planetary Phases

• Only planets that are always closer to the sun
  will show phases when viewed from the Earth.
• Planets orbiting further from the sun than the
  Earth will always appear full.

11
Heliocentric Theory Prevails

• Since Galileos theory clashed with the religious
  views of the time, he underwent many trials and
  tribulations, eventually being sentenced to house
  arrest for his remaining years.
• But his view has withstood the test of time.
• Today we talk about our solar system, not our
  Earth system

12
Tycho Brahe

• (1546-1601CE) A Danish astronomer who was not
  happy with the accuracy of the astronomical
  observations of his and earlier times.
• Created his own instruments and made very
  detailed observations of the heavens for over 20
  years.

13
Johannes Kepler (1571-1630)

• German mathematician who used Brahes data to
  compute the actual orbit of the planets.
• He discovered that the planets do not orbit in
  circles, but in ellipses.

14
Keplers Laws

• Keplers three laws enabled astronomers to
  figure out the orbits of the planets.
• But while he could now predict where a planet
  would be on a given day, he had no idea what made
  them move in almost circular paths.

15
Sir Isaac Newton (1643-1727)

• Famous for his three laws of motion and the Law
  of Universal Gravitation.
• Newtonian physics is used today to send the
  shuttle into orbit, space probes to the stars,
  and the Apollo astronauts to the moon.
• Was the first to show how objects could be put
  into orbit around our planet.
• If I have seen further than others, it is by
  standing upon the shoulders of giants.

• One of the greatest scientists in history.
• Studied light and optics, astronomy, motion,
  thermal dynamics, and many other things.
• When he couldnt find mathematics powerful enough
  to solve his gravity and planetary orbit
  problems, he created his mathematics, which we
  call calculus today.

16
Inertia

• Inertia is the property of matter to resist any
  change in motion.
• An object at rest will remain at rest, while an
  object in motion will remain in motion in a
  straight line at a constant speed until acted on
  by an outside force.

17
Gravity

• Gravity is the force of attraction between any
  two objects with mass.
• The more mass, the more gravity.
• The further apart the two objects are, the less
  gravity.

18
Newtons Law of Gravity

• Newton realized that the moon should go in a
  straight line forever and ever.
• But the force of gravity kept pulling it towards
  the Earth.
• The moon is going fast enough that it keeps
  curving around the Earth.
• It is constantly falling towards the Earth.

19
Newton and Kepler

• Newtons combined Keplers Third Law with his Law
  of Gravity.
• Now he could figure out the masses of the other
  planets if he knew how far they were from the sun
  and the time it takes them to make one orbit.

20
Solar System

• There are nine planets in our solar system.
• Mercury is 58,000,000-km from the sun.
• Pluto is 5,913,000,000-km from the sun.
• These numbers are hard to use!

21
Astronomical Units

• We will use AUs to measure distances in the
  solar system.
• The Earth is about 150,000,000-km (93,000,000
  miles) on average from the sun.
• So we will call this distance 1 AU.

22
Planetary Distances

• Mercury 0.4 AU
• Venus 0.7 AU
• Earth 1.0 AU
• Mars 1.5 AU
• Jupiter 5.0 AU
• Saturn 10.0 AU
• Uranus 19.0 AU
• Neptune 30.0 AU
• Pluto 39.0 AU

• Light travels through space at 300,000-km/s.
• So it takes about 8 minutes for light from the
  sun to travel 1 AU and reach us.
• How long would it take light from the sun to
  reach Pluto?
• 39 x 8 312 minutes, or 5.2 hours!

23
The Sun
24
Mass of the Solar System

• Almost all the mass in our solar system is in the
  sun.
• Mass of the Solar System
• Sun 99.80
• Jupiter 0.10
• Comets 0.05
• Other 8 planets 0.04
• Total of Sun Planets Comets 99.99

25
Solar Facts

• Is just a medium sized star (yellow dwarf). It is
  about 1.4 million kilometers in diameter
• It would take 10 Jupiters or 109 Earths to fit
  across the Sun!
• Makes life on our planet possible by giving us
  great amounts of light and heat.

26
Composition

• The sun is mainly composed of hydrogen and
  helium.
• 90 hydrogen
• 9 helium
• Small amounts of the elements up through iron.
• This changes over time as the sun converts
  hydrogen to helium by fusion.

27
Fusion

• The process of combining the nuclei of small
  atoms into one larger atom.
• This process gives off enormous amounts of
  energy.
• Mass is actually converted into energy (Emc2).

28
Fusion in the Sun

• It takes enormous heat and pressure to fuse even
  the lightest elements.
• Our sun can fuse elements up to atomic number 8.
• It would take larger stars to create elements
  larger than oxygen.
• Our sun has enough hydrogen to fuse for another 5
  billion years.

29
The Suns Layers

• 1. Core This is the center layer of the sun.
  This is where all the sun's heat and light is
  made. 15 million C.
• 2. Radiative Zone The heat and light move from
  the core into this layer.
• 3. Convection Zone In this layer, the gases move
  like boiling water. This moves them from the
  inner parts of the Sun to the outer part of the
  sun that we see. About 6400 C.

30
Suns Outer Layers

• 4. Photosphere This is the part of the sun we
  see. This layer gives off the heat and light from
  the sun. The cooler parts of this layer make
  sunspots.
• 5. Chromosphere This layer shoots out hot gases.
• 6. Corona This layer can only be seen during an
  eclipse. It is the atmosphere around the sun.
• These layers are called the Suns atmosphere.

31
Exploring the Sun
32
Sunspots

• Sunspots look like small, dark areas on the suns
  surface.
• They are areas of gas that are cooler than the
  surrounding gases. They dont give off as much
  light, so they look darker.
• Created by the Suns magnetic field.

33
Sunspot Activity

• The numbers of sunspots changes regularly,
  reaching a maximum number every 11.2 years.
• This coincides with the Suns magnetic field
  reversing every 11.2 years.
• Could be responsible for short term climate
  changes.

34
Solar Flares

• Enormous explosions on the surface of the Sun.
• Occur near sunspots when the loops in suddenly
  connect.
• Release particles and radiation that can reach
  the Earth.
• Can interfere with communications and damage
  satellites.

35
Prominences

• Sunspots usually occur in pairs.
• Prominences are reddish loops of gases that
  follow the magnetic lines.

36
Little Ice Age

• During the late 1600s almost all solar sunspot
  activity stopped. For 60 years there was almost
  no sunspot activity.
• Scientists do not know why this happened.
• The weather in Europe and North America was much
  colder than usual.

37
The Inner Planets
38
Planetary Zones

• First Zone Contains the rocky terrestrial
  planets Mercury to Mars.
• Asteroid belt divides the first and second zones.
• Second Zone Contains the gas giants Jupiter
  through Neptune.
• Third Zone Goes from the orbit of Neptune out to
  50 AU. Includes Pluto and the ice dwarfs in the
  Kuiper Belt.

39
The Inner Planets

• Planets are rocky.
• Called terrestrial from the Latin word terra,
  which means Earth.

40
Mercury

• Roman name for the Greek messenger god. He wore
  winged sandals so he could fly. Since Mercury
  the planet is the fastest of all the planets this
  is appropriate.

41
Mercury Data

• Closest to the sun.
• Temperature ranges from 427C in daylight to
  -173C at night.
• Revolves slowly, in two Mercury years three
  Mercury days will have passed.
• Essentially no atmosphere.
• Surface similar to the moon, with craters and
  smooth plains.
• One third the size of the Earth.

42
Mercury

• Diameter one third the size of Earth
• Distance 0.4 AU
• Atmosphere no atmosphere
• Features Craters with smooth plains and most
  extreme temperature range
• Lifeno life because of atmosphere

43
Venus

• Named for the Roman goddess of love and beauty.
  Originally the Greek goddess Aphrodite.

44
Venus Temperature

• Almost same size as the Earth.
• Hottest surface in our solar system. The average
  daytime surface temperature is 464C, compared to
  the Earths 15C.
• This is hot enough to melt lead.

45
Venus Atmosphere

• Seen from Earth, Venus is completely cloud
  covered.
• Venus has an very thick atmosphere, about 96
  CO2, and 4 N2.
• The clouds are mainly sulfuric acid.
• The atmospheric pressure is 92 atmospheres,
  compared to the one atmosphere we experience on
  Earth.
• This is the pressure you would feel if you were
  under 915 meters of water!

46
Greenhouse Effect

• Venus is the classic example of the runaway
  greenhouse effect.
• Water on Earth helped tie up much of the CO2 in
  rocks. Life also stored CO2 in plants and shells
  of animals.
• Venus was probably too warm to have much water in
  the liquid state, so the water vapor added to the
  greenhouse effect.
• As the rocks got hotter, they released their CO2
  into the air also.
• So the greenhouse effect got worse and worse.

47
Venus Motions

• Since Venus takes 7.5 Earth months to revolve
  around the sun and 8 months to rotate once on its
  axis, a day on Venus is longer than its year.
• Venus also rotate east to west, the only planet
  to do so. This retrograde rotation (backward)
  was probably caused by Venus being struck by a
  large object early in its history.

48
Venus Surface

• Since we cant see through the clouds on Venus,
  we use radar to scan the surface.
• Venus has rocks, mountains, craters, and strange
  dome shape landforms not found on other planets.

49
Venus Explorations

• About 20 spacecraft have visited Venus, with more
  either on the way or planned.
• Some have even landed on the surface and sent
  back pictures for a short while.

50
The Evening Star

• When in the west at sunset, Venus will be the
  brightest object in the sky.
• This is because Venus has the highest albedo
  (0.76) of all the planets. Albedo is the percent
  of light reflected by an object.
• Our moon has an albedo of 0.07, so it reflects
  very little of the light that strikes it.
• Also called the morning star when it is in the
  east.

51
Venus

• Diameter 0.9 Earth
• Distance 0.7 AU
• Atmosphere 96 carbon dioxide at 0.01
  atmospheres.
• Features hottest surface in solar system.
  Retrograde rotation.
• Life Very doubtful, the pressure and
  temperatures are too high. Sulfuric acid in
  atmosphere does not help either.

52
Earth

• Diameter 1 earth
• Distance 1 AU
• Atmosphere 78 Nitrogen, 21 Oxygen
• Features water world, moderate temperature and
  pressures
• Life teeming with life. Planet is just right
  for life as we know it.

53
Mars

• Mars is the Latin name for Ares, the Greek god of
  war.

54
Mars Atmosphere

• Mars has an atmosphere that is mainly carbon
  dioxide.
• It is very thin, only 0.01 atmospheres at the
  surface.
• Mars even has clouds, but they are thin also.
• The winds can create dust storms that cover much
  of the planet and last for months.

55
Mars Volcanoes

• Mars surface has a wide variety of landscapes.
• Olympus Mons is the largest volcano in our solar
  system. Its base would cover the state of
  Colorado.
• It is three times taller than Mt. Everest.
• There are many other volcanoes on Mars, but none
  seem to be active at this time.

56
Mars Canyons

• Valles Marineris is an enormous canyon on the
  equator of Mars. It is over 4000-km long. This
  would reach from Los Angles to Chicago!

57
Mars Landscape

• Mars seems to have dried river and lake beds,
  deltas, and other features that make scientists
  think Mars had abundant water early in its
  history.
• If there was water it is possible that life could
  have existed on Mars, and still might.

58
Mars Data

• Mars is about half the size of the Earth.
• A 100 pound sixth grader would weigh 39 pounds on
  Mars.
• It is very cold on Mars, with the average
  temperature ranging from -140 C to 20 C.
• Mars has two very small moons, Phobos and Diemos.
• They are named after the horses that pulled
  Marss chariot.
• The larger Deimos is only 23-km in diameter.

59
Mars Missions

• There have been many missions to Mars, starting
  with the Viking craft in 1976.
• There are currently two orbiters and two rovers
  collecting data on Mars.
• Manned missions are also currently being planned,
  around 2025 or so.

60
Mars

• Diameter 0.5 Earth
• Distance 1.5 AU
• Atmosphere 96 carbon dioxide at 0.01
  atmospheres.
• Features large canyons, volcanoes.
• Ancient dried up lakes, streams, rivers, and
  seas.
• Life Possibly ancient life when there was liquid
  water on the planet. Could still exist under the
  sand.

61
The Outer Planets
62
Gas Giants

• Separated from the 1st zone by the asteroid belt,
  the 2nd Zone contains the gas giants.
• Made of the lightweight elements Hydrogen,
  Helium, Carbon, Oxygen, and Nitrogen.
• All are much larger than the Earth, with 15-300
  times the mass, and 4-11 times the diameter.
• Not believed to have solid surfaces.
• Have rings and many satellites.

63
Gas Giants Atmospheres

• Since they have so much mass, their strong
  gravity can keep even light gases from escaping.
• Atmosphere tends to resemble the sun (75 H, 24
  He, 1 other gases).
• No well defined surface. Gases just get denser
  and denser as you go deeper. Becomes liquid
  metallic hydrogen, which has properties of
  liquids and metals. Exist only under high
  pressure. Causes Jupiter's magnetic field.

64
Gas Giants Cores

• Gas giants are believed to have solid cores made
  of rock,, ice, frozen carbon dioxide, and other
  compounds.
• Cores would be several times the size of the
  Earth.

65
Jupiter, King of the Roman Gods

• Named for Jove, the King of the Roman Gods.
• Roman name for the Greek god Zeus.
• Often the term Jovian is used to describe things
  pertaining to Jupiter. Example the Jovian
  moons.

66
Jupiter

• Believed to be a failed star, lacking the mass to
  become a small star.
• Most massive planet in solar system.
• Has over 60 satellites.
• Density is 1.33g/cm3.
• Rotates every 10 hours.
• Takes 12 years to orbit the sun.
• Gravity almost 2.5 times that of the Earth.

67
Jupiter

• Diameter 11 earth's
• Distance 5 Au
• Atmosphere mainly hydrogen with a some helium
• Features active weather with storms that last
  for 100s of years
• Lifenone

68
Jupiter Atmosphere

• Mainly hydrogen with some helium.
• Very active weather systems.
• Forms colorful bands and swirls.
• Has hurricanes that last for 100s of years.

69
Great Red Spot

• The red spot is a huge storm that has been
  continuously going on Jupiter for over 400
  years.  Winds inside this storm reach speeds of
  about 270 mph.  With a diameter of 15,400 miles,
  this storm is almost twice the size of the entire
  Earth.

70
Jupiter's Moons

• Galileo discovered the four largest. Io,
  Ganymede, and Callisto are larger than our own
  moon.
• Europa has a icy crust and is believed to have
  liquid water oceans below the frozen surface.
• Io has many active volcanoes.

71
Missions to Jupiter

• http//www.windows.ucar.edu/tour/link/jupiter/spa
  ce_missions.html
• http//www.solarviews.com/eng/craft2.htmjupiter

72
Shoemaker Levy 9

• In July 1994, Comet Shoemaker-Levy 9 collided
  with Jupiter with spectacular results (left). The
  effects were clearly visible even with amateur
  telescopes. The debris from the collision was
  visible for nearly a year afterward with HST.
• Captured by Jupiter's strong gravity, the comet
  was torn into over 20 fragments that struck
  Jupiter, each with a force of millions of
  megatons of energy.
• This has renewed NASAs interest in tracking
  objects that might get close to Earth one day.

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Saturn the God

• Saturn was the Roman God of the Harvest and of
  Time.
• Father of Jupiter, Neptune, and Pluto.
• The Roman name for the Greek god Cronos.
• Saturnalia was the mid-winter festival in Saturns
  honor. It lasted seven days, and there was much
  merrymaking. Public business was suspended and
  schools were closed. Parents gave presents to
  their children.

74
Saturn Facts

• 2nd largest planet in solar system.
• A day on Saturn is a little over 10 hours long!
• It takes 29 years to orbit the sun.
• Almost 10 times larger than Earth.
• Most visible rings of any planet.
• Density is 0.69 g/cm3.
• If a large enough ocean could be found, Saturn
  would float in it!

75
Saturn Atmosphere

• Similar to Jupiters, mostly hydrogen with some
  helium.
• Storms not as large or as long lived as
  Jupiter's.
• Clouds are thicker, blocking views to lower
  layers. Explains the lack of banding compared to
  Jupiter.

76
Saturns Rings

• Very spectacular. Not at all solid.
• Made of tiny bits of ice, dust, and rock. A few
  are up to a kilometer across.
• Only about a kilometer thick.
• The Cassini space probe actually passed through
  the outer ring as it slowed down to enter orbit.

77
Saturns Moons

• Has over 40 moons, 15 or so that are large enough
  to be called major moons.

78
Titan

• Titan has an atmosphere made of about 99
  nitrogen and 1 methane.
• Has a pressure of 1.6 atmospheres.
• Completely covered by thick clouds that are
  similar to smog on Earth.
• The second largest moon, it is larger than Pluto
  and Mercury.

79
Cassini-Huygens

• The Huygens probe actually parachuted into the
  atmosphere of Titan on 14 January 2005.
• It took pictures and collected data all the way
  to the surface. It survived the landing and sent
  back pictures of the surface it landed on.

80
Saturn

• Diameter 9 times larger than Earth
• Distance 10 Au
• Atmosphere 96 Hydrogen 4 Helium
• Features Has short storms, rings orbit it that
  are made up of bits of ice, dust, and rock
• Lifeno life

81
Uranus the God

• URANUS Great primeval God of the Sky. Born of
  GAIA, the Earth, he covered the world in the form
  of a vast bronze dome and ruled over everything.

82
Uranus Facts

• Diameter is like 4 Earths.
• Mass is 14.5 Earths.
• Takes 84 years to revolve around the sun.
• Day is a little over 17 hours long.
• Has more than 20 moons.

83
Uranus Axis

• Uranus is considered unusual because the planet
  is tipped on its side. The poles actually point
  towards the Sun. This is due to the fact that its
  magnetic field is tilted 60 degrees from the axis
  of rotation.
• It is believed that Uranus was struck by a large
  object that knocked Uranus on its side.

84
Uranus Seasons
85
Uranus Atmosphere

• First, there is absolutely no detail in the cloud
  cover. Only when pushed to the maximum level of
  color enhancement and contrast on computers do
  scientists start to see small swirls in the
  atmosphere.

86
Uranus Moons

• 5 large and many small moons.
• Titania is the biggest moon of Uranus. It is
  about half the size of our moon. Titania is
  covered by many small craters, a few huge impact
  basins ice cliffs, and fault lines.
• Ariel The brightest moon of Uranus. Youngest
  surface of Uranus' moons, the least cratered. Has
  long valleys and canyons.

87
Uranus

• Diameter4 Earths
• Distance19 Au
• Atmosphere82 Hydrogen 15 Helium
• Features extreme seasons because axis is tipped
  on its side and no detail in cloud cover
• Lifeno life, too cold, atmosphere and surface
  would not allow life as we know it.

88
Uranus

• Diameter 3.6 times larger than Earth
• Distance 19 Au
• Atmosphere 82 Hydrogen 15 Helium
• Features extreme seasons and axis is tipped on
  side
• Lifeno life

89
Neptune the God

• Neptune is the Roman god of the sea.
• The Romans modeled him after the Greek god
  Poseidon.

90
Neptune

• Neptune revolves on its axis every 18 hours.
• It takes 165 years to revolve around the sun
  once.
• Has the mass of 17 Earths.
• Has 13 moons.
• Diameter is almost 4 times larger than Earths.
• Blue-green color is from the methane in the
  atmosphere.
• At times it is the furthest planet from the sun.

91
Neptune Atmosphere

• 80 hydrogen, 19 helium, and 1.5 methane.
• Has icy clouds and enormous storms.
• Has the fastest winds in our solar system.

92
Triton

• Neptune's largest moon is named Triton. Triton is
  much larger than any of the planet's other moons.
• Triton is a very cold place, so the moon is
  covered with ice. Even though Triton is cold
  there is a lot going on there. It has geysers
  like the ones at Yellowstone Park on Earth.
• The geysers shoot ice 8 km (5 miles) high into
  Triton's thin atmosphere! There may be water
  under the ice at Triton. It is even possible that
  there might be life in that water. The interior
  of Triton is probably geologically active.

93
Neptunes Rings

• Neptune's rings are much darker than Saturn's
  bright rings.
• Saturn's rings are made of ice, which reflects
  lots of light. Neptune's rings are probably made
  of rocks and dust.
• Rocks and dust don't reflect as much light.

94
Neptune

• Diameter 4 times the size of Earth
• Distance 30 Au
• Atmosphere 80 Hydrogen 19 Helium 1.5 Methane
• Features At times it is the furthest planet from
  the sun. Icy clouds and enormous storms
• Lifepossible life on one of its moons called
  Triton

95
Pluto the God

• Pluto was the Roman name for Hades, the Greek god
  of the Underworld.

96
Pluto Facts

• Usually the furthest planet from the sun.
• 2/3rds the size of our moon.
• Has one moon, Charon.
• So cold that oxygen and nitrogen in its
  atmosphere is frozen solid.
• Only planet not visited by a spacecraft.
• Pluto takes 248 years to make one orbit around
  the sun!

97
Plutos Atmosphere

• When Pluto comes close enough to the sun, the
  surface of solid Nitrogen sublimates to produce a
  substantial atmosphere with winds and clouds.
• Because the planet is so small, however, it does
  not have enough gravity to bind an atmosphere for
  very long. Thus Pluto's atmosphere is being
  rapidly produced and rapidly lost at the same
  time.
• This means that the atmosphere is not in
  equilibrium.

98

• Pluto has the most eccentric orbit of all the
  planets in the solar system. Its orbit takes it
  to 49.5 AU at its farthest point from the Sun.
  And its orbit takes it as close as 29 AU to the
  Sun.
• That means that Pluto's orbit draws within the
  orbit of Neptune, as can be seen in this drawing,
  making Pluto the 8th planet rather than the 9th
  planet for roughly 20 years at a time.
• Pluto was the 8th planet from January 1979 to
  February 1999. Neptune is now the 8th planet for
  over 200 years!

99
Charon

• Named for the boatman who ferried the dead into
  the Underworld.
• Surface seems to be covered with water-ice
  instead of Plutos nitrogen-ice.
• Largest moon compared with its planet.

100
Pluto Debate

• Is Pluto really a planet?
• Pluto is small that many scientists now consider
  Pluto just another Kuiper Belt object, which are
  small icy worlds in the third zone.
• Many have been discovered so far, and it is
  believed there are thousands more out there.
• In July 2005 a KBO larger than Pluto was
  discovered. Named Sedna after the Inuit goddess
  of the ocean.

101
Pluto

• Diameter 0.2
• Distance 29 Au
• Atmosphere Oxygen and nitrogen atmosphere
• Features most eccentric orbit
• Lifetoo cold.no!

102
Comets, Asteroids, and Meteors

• 20-5

103
Comets

• Comets are chunks of ice and dust whose orbits
  are very long, narrow ellipses.
• Often thought of as dirty snowballs.

104
Comet Orbits

• Most comets are on very eccentric orbits that
  seldom pass near the Earth.

105
Comet Structure

• Nucleus main solid core of the comet.
• Tail gas and dust particles released by the
  comet. They are pushed by the soar wind away
  from the sun.
• Coma gases and dust released by the comet when
  energy from the sun heats the comet and causes
  the solid materials to turn into a gas.

106
Periodic Comets

• Comets that repeatedly orbit into the inner solar
  system are periodic comets.
• Comet Halley is a famous, short period comet. It
  appears every 76 or so years.
• Nucleus of Halleys comet taken by the Giotto
  spacecraft.

107
Halleys Comet

• Last appeared in 1985-86. Should appear again in
  2061.
• Like most comets it has a very eccentric orbit.

108
Asteroids

• Asteroids are rocky or metallic objects, most of
  which orbit the Sun in the asteroid belt between
  Mars and Jupiter. A few asteroids approach the
  Sun more closely. None of the asteroids have
  atmospheres.
• Asteroids are also known as planetoids or minor
  planets.

109
Comet Clouds

• Most comets are from one of two clusters, the
  Kuiper Belt and the Oort Cloud.
• The Kuipier Belt is close to Pluto, from 30 to 50
  AU from the sun.
• The Oort Cloud is material left over from the
  formation of the solar system and is more than
  100,000 AU from the sun.

110
Asteroid Belt

• The asteroid belt is a doughnut-shaped
  concentration of asteroids orbiting the Sun
  between the orbits of Mars and Jupiter, closer to
  the orbit of Mars.
• Most asteroids orbit from between 186 million to
  370 million miles (300 million to 600 million km
  or 2 to 4 AU) from the Sun.
• The asteroids in the asteroid belt have a
  slightly elliptical orbit. The time for one
  revolution around the Sun varies from about three
  to six Earth years.

111
Number of Asteroids

• There are about 40,000 known asteroids that are
  over 0.5 miles (1 km) in diameter in the asteroid
  belt.
• About 3,000 asteroids have been cataloged. There
  are many more smaller asteroids.
• The first one discovered (and the biggest) is
  named Ceres it was discovered in 1801.

112
Asteroid Size

• Asteroids range in size from tiny pebbles to
  about 578 miles (930 kilometers) in diameter
  (Ceres).
• Sixteen of the 3,000 known asteroids are over 150
  miles (240 km) in diameter.
• Some asteroids even have orbiting moons.

113
Origin of the Asteroid Belt

• The asteroid belt may be material that never
  coalesced into a planet, perhaps because its mass
  was too small.
• The total mass of all the asteroids is only a
  small fraction of that of our Moon (about
  1/30th).
• A less satisfactory explanation of the origin of
  the asteroid belt is that it may have once been a
  planet that was fragmented by a collision with a
  huge comet.

114
Near-Earth Asteroids

• Asteroids whose orbits bring them within 1.3 AU
  of the Sun are called Near-Earth Asteroids (NEA)
  or Earth-Approaching asteroids.
• These asteroids probably came from the main
  asteroid belt, but were jolted from the belt by
  collisions or by interactions with other objects'
  gravitational fields (primarily Jupiter).

115
NEA Concerns

• About 250 NEAs have been found so far, but many,
  many more exist.
• The largest known NEA is 1036 Ganymede, with a
  diameter of 25.5 miles (41 kilometers).
• According to astronomers there are at least 1,000
  NEA's whose diameter is greater than 0.6 miles (1
  kilometer) and which could do catastrophic damage
  to the Earth.
• Even smaller NEA's could cause substantial
  destruction if they were to collide with the
  Earth.

116
Demise of the Dinosaurs?

• An asteroid impact with the Earth may have caused
  the extinction of the dinosaurs.
• The Alvarez Asteroid Theory explains the huge K-T
  mass extinction 65 million years ago by a large
  asteroid hitting the Earth off the Mexican
  Yucatan peninsula.
• This impact would have caused severe climactic
  changes leading to the demise of many groups of
  organisms, including non-avian dinosaurs.

117
Meteoroids

• Meteoroids are small chunks of dust and rock in
  space.
• Usually come from comets or asteroids.

118
Meteors

• When a meteoroid enters the Earths atmosphere
  friction will cause it ti heat up.
• It will leave a bright streak of light across the
  sky as it burns up.
• Are called meteors when they brightly fall to the
  Earth.
• Often occur in showers, with several sightings a
  minute.

119
Meteorites

• While the vast majority of meteors burn
  completely up, ones that are large enough pass
  through the atmosphere and hit the surface.
• Most look like stones, so they are not noticed.
  Some are easy to identify as they are made of
  iron or nickel.

120
Craters

• Meteorites create craters when they strike the
  surface of a planet.
• Our moon is covered with craters caused by
  meteorites, asteroids, and comets.
• Meteor Crater in Arizona is a famous crater found
  in the USA. Occurred 50,000 years ago.
• Hit with the force of 150 Hiroshima A bombs.

121
Is There Life Beyond Earth?

• 20-6

122
Extraterrestrial Life

• Life from or on other planets.
• Life not from this Earth.
• A meteorite recently found in Antarctica has tiny
  fossilized shapes that might be fossils, the
  remains of ancient life. And this meteorite came
  from Mars!

123
The Goldilocks Conditions

• Scientists refer to life as we know it.
• Most life on Earth requires liquid water and a
  suitable temperature and atmosphere.
• That is its not too hot, its not too cold,
  its just right!

124
Just Right!

• If the Earth were much hotter, water would always
  be water vapor, a gas.
• If the Earth were much colder, water would always
  be ice, a solid.
• But water can exist in all three states, because
  our temperature is just right!

125
Life on Earth

• Scientists are not sure if all life would have to
  be like life on Earth.
• Life on Earth exists even in hot springs and near
  volcanic vents.
• Maybe life can survive outside the Goldilocks
  Zone.

126
Life on Mars?

• Since Mars is similar to earth it is an obvious
  place to start looking.
• Spirit and Opportunity have both found signs that
  show Mars once had a fair amount of liquid water.
• If Mars once had water, maybe life evolved there
  also.

127
Life on Europa?

• While Europas surface is frozen, it appears that
  there might be liquid water below the surface.
• Heat from inside Europa could keep the water
  liquid.
• Where there is liquid water, there might be life.

128
SETI

• Search for Extraterrestrial Intelligence.
• Astronomers listen for radio signals from space.
• Intelligent races should have radios, so might
  try to contact others.