Chapter 16: The Solar System Part 1

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Chapter 16 The Solar System Part 1

• Alyssa Jean-Mary

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Stars vs. Planets

• To us, stars appear as points of light since they
  are so far away from us. The planets, however,
  appear to us as disks since they are much closer
  to us than the stars.
• The stars glow brightly because they are
  extremely hot. The planets dont shine by
  themselves because they are too cool, so what is
  seen is the sunlight being reflected from them.
• The solar system is composed of the sun, its
  accompanying planets, the satellites of these
  planets, and other smaller bodies.
• The members of the solar system are in emptiness
  and are very far from everything else in the
  universe.

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The Family of the Sun

• Until 1609, the solar system was thought to
  consist of only five planets besides the sun, the
  earth, and the moon.
• When Galileo built his own telescope, he found
  four additional members of the solar system. What
  he found were the brighter of the moons, which
  are also referred to as satellites, that circle
  Jupiter.
• With the improvement of telescopes, many
  additional members of the suns family have been
  discovered since Galileos discovery.
• There were nine planets, in order of their
  distance from the sun Mercury, Venus, Earth,
  Mars, Jupiter, Saturn, Uranus, Neptune, and
  Pluto. Now, however, Pluto is no longer referred
  to as a planet. All of the planets, except for
  Mercury and Venus have satellites, or moons.
• Between Mars and Jupiter, thousands of small
  objects called asteroids follow their own orbital
  around the sun. Asteroids each are less than 1000
  km in diameter.
• Comets and meteors are also part of our solar
  system.
• The knowledge that we have of our solar system
  has been greatly increased by the voyages of
  spacecraft. Spacecraft have landed on Venus and
  Mars, and astronauts have walked on the moon.

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The Solar System 1

• In addition to the solar system being isolated
  from the rest of the universe, the principal
  members of the solar system are far from each
  other.
• For instance, the earths nearest neighbor is the
  moon, and the moon is about 384,000km away from
  the earth. The sun is about 150 million km away
  from the earth. In perspective, Apollo 11 took 3
  days to reach the moon. If Apollo 11 was
  traveling at the same speed, it would take it
  more than 3 years to reach the sun.
• All of the planets revolve around the sun as well
  as rotate on their axes
• Almost all of the revolutions and rotations of
  the members of the solar system are in the same
  direction. Only the rotation of Venus and the
  revolutions of a few minor satellites about their
  parent planets are contrary to this direction.
• All the orbits lie nearly in the same plane. Only
  the orbits of comets dont.

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The Solar System
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The Planets
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Inner Planets and Outer Planets

• The inner planets are Mercury, Venus, Earth, and
  Mars. They are all relatively small, with similar
  densities. They are also all composed largely of
  rocky material, with cores most probably
  consisting mainly of iron. They all rotate fairly
  slowly on their axes. There is only one satellite
  of any size around these planets, which is the
  moon. As was stated before, Mercury and Venus
  dont have any satellites, and the two satellites
  that are around Mars are only a few km across.
  These planets have low escape speeds.
• The outer planets are Jupiter, Saturn, Uranus,
  and Neptune. These planets are large, but not
  very dense when compared to the earth. They are
  composed largely of gases compressed to liquid
  form without iron cores. They all rotate fairly
  rapidly on their axes. There are a total of over
  130 satellites around these planets. A few of
  these are large, but most of them are quite
  small. They also have high escape speeds.

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The Inner Planets Mercury 1

• Mercury was named after the fleet-footed
  messenger of the gods in classical mythology. It
  was named as such because Mercurys position
  relative to the stars changes rapidly. Thus, the
  symbol of Mercury is a representation of a winged
  helmet.
• Mercury is the planet that is closest to the sun,
  the innermost planet. It thus always appears as a
  companion to the sun. Mercury is hard to see
  during the day since it is so close to the sun,
  so the best times to view Mercury is near sunrise
  and sunset. On Earth, Mercury appears to show
  phases, just like the moon shows phases. This is
  because the orbit of Mercury lies within the
  orbit of the earth. Mercurys diameter appears to
  be about 3 times greater when it is closer to the
  earth than when it is farther away from the
  earth.
• Mercury takes 59 of our days to make a complete
  rotation on its axis, and it takes 88 of our days
  to make a complete revolution around the sun.
  Thus, a day on Mercury is 176 of our days.
• Because Mercury has long days and is so close to
  the sun, on the sunlit side of Mercury, the
  temperatures are high, as high as 425C. There is
  almost no atmosphere on Mercury, and thus, there
  is no transfer of heat from the sunlit side to
  the dark side and no trapping of heat that is
  radiated from the surface of Mercury. Because of
  this, the night temperature can be as low as
  -180C. The only gases that are found near
  Mercury are the inert gases helium, argon, neon,
  and xenon. There are only trace amounts of these
  gases. Thus, Mercury is altogether an
  inhospitable place.

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The Inner Planets Mercury 2

• In 1974, Mariner 10 passed within a few hundred
  kilometers of Mercury. It thus sent back
  photographs as well as various kinds of data.
• These photographs showed that Mercury has a
  surface that is pocked by meteoroid craters, a
  surface much like the surface of the moon. The
  rugged landscape of Mercury has many hills and
  valleys in addition to the craters.
• There is no evidence that Mercury has ever
  melted, which presents a problem based on other
  evidence of Mercury. The crust of Mercury appears
  to be composed of silicate rocks. These rocks
  have densities that are much lower than the
  rather high density of the planet as a whole.
  Because of this, the interior of Mercury is
  probably an iron-rich core, just like that of the
  earth, only considerably larger in proportion to
  Mercurys size. Also, Mercury has a fairly strong
  magnetic field. This suggests that at least part
  of the core is a liquid even now. But, if Mercury
  has never melted after it was formed, then how
  did the heavy and light constituents separate,
  and why is the core molten today?

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The Inner Planets Venus

• Venus was named after the Roman goddess of love
  and beauty. Thus, the symbol of Venus is a
  representation of the traditional symbol of a
  mirror.
• Besides the sun and the moon, Venus is the
  brightest object in the sky. Venus can sometimes
  be seen during the day. Because the orbit of
  Venus lies within the orbit of the earth, just
  like for Mercury, Venus never appears very far
  away from the sun. Thus, it appears alternately
  as a morning star and an evening stark. Since
  Venus is usually farther from the sun than
  Mercury, it is visible for longer periods than
  Mercury.
• If you look downward on the north pole of Venus,
  it is rotating clockwise about its axis. This is
  unlike the earth and the other planets, which all
  rotate counterclockwise about their axes. Thus,
  Venus is said to spin backward on its axis.
  Venus rotates extremely slow on its axis, and
  thus, one day on Venus is 243 of our days.

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The Inner Planets Venus Its Surface

• The size and mass of Venus is closer to the
  earths size and mass than any other member of
  the family of the sun.
• The surface of Venus has mountains, craters, and
  fault-like cracks.
• It has two major highland regions, the larger of
  which is about the size of the United States.
  These two continents only cover about 5 of the
  surface of Venus, in contrast to the 30 that is
  covered by continents on the earths surface.
  Also, unlike the continents on Earth, the
  continents on Venus have no water lapping their
  edges.
• Some of the mountains on Venus are quite high,
  and one of them is even higher than Mount
  Everest.
• There is a lot of evidence of volcanism volcanic
  peaks, extensive lava flows, and a huge volcanic
  crater about 100km across.
• There is no evidence, however, that the crust of
  Venus consists of huge shifting plates like that
  of the earth. This is odd since Venus and Earth
  are otherwise very similar to each other. Maybe
  it is due to the absence of water on Venus,
  since, on Earth, it is thought that water in the
  rock of the plates might help the plates to bend,
  and thus be tugged across the surface by the
  weight of their sinking edges.

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The Inner Planets Venus Meteoroids

• Meteoroids that are less than a kilometer across
  will be burnt up in the dense atmosphere of
  Venus, but larger ones can pass though to impact
  the surface of Venus. Because of this, there
  should be more impact craters from larger
  meteoroids on the surface of Venus than the 968
  that have been seen from spacecraft. But, since
  Venus is so hot, there is no liquid water to
  cause erosion on the craters. Also, there is no
  evidence of alteration by volcanic or tectonic
  activity. Thus, something had to happen a
  half-billion years ago to blot out the impact
  craters that had existed. It is thought that
  immense lava flows paved over the surface of
  Venus one or more kilometers deep. Since the
  earth uses much of its internal heat to shape and
  reshape the lithosphere, there is little heat for
  volcanism, so what happened to Venus is unlikely
  to happen to the earth. On Venus, however, there
  is no plate activity to prevent volcanism.

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The Inner Planets Venus Life?

• The information obtained from instruments on
  spacecraft show that the atmosphere of Venus is
  almost entirely composed of carbon dioxide, with
  a little nitrogen and only traces of other gases.
  
• Venus is permanently shrouded in thick
  lemon-yellow clouds. These clouds contain mainly
  sulfuric acid droplets, and are driven by strong
  east-to-west winds.
• The pressure of the atmosphere at the surface of
  Venus is about 90 times that for the earth.
• On Earth, the small amount of carbon dioxide that
  is contained within the atmosphere absorbs a lot
  of the radiation from the ground. This also
  happens on Venus, but, because of the amount of
  carbon dioxide that blankets Venus, its surface
  temperature averages well over 400C, almost as
  high as the temperature on the sunlit side of
  Mercury.
• Thus, it seems impossible that life exists on
  Venus.

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The Inner Planets Mars

• Mars is second to Venus in brightness when it is
  closest to us. Since it seen from Earth as
  reddish-orange in color, it has always been
  associated with violence and disaster. Thus, Mars
  was named after the Roman god of war. And thus,
  the symbol of Mars is a circle with an arrow,
  which is a representation of the conventional
  male symbol.
• The diameter of Mars is slightly over half the
  diameter of the earth. The mass of Mars is 11 of
  the mass of the earth. Thus, the surface gravity
  of Mars is about 38 of the surface gravity on the
  earth. For example, if an astronaut weighs 150lb
  on the earth, the astronaut would weigh 57lb on
  Mars.
• The overall density of Mars is 3.97 g/cm3,
  compared to the overall density of the earth,
  which is 5.52 g/cm3. The reason for this
  difference is because the materials in the
  interior of Mars are not compressed as much as
  the materials in the interior of the earth. Thus,
  it is thought that Mars probably has
  approximately the same composition as the earth.
• The amount of time that it takes Mars to rotate
  on its axis is a little over 24 hours. The amount
  of time that it takes Mars to revolve around the
  sun is almost 2 years. Mars axis is inclined to
  the plane of its orbit at nearly the same angle
  as the earths axis. Thus, the day and night on
  Mars is about the same length as the day and
  night on earth. Also, the season on Mars are
  about 6 months long, and at least as pronounced
  as the seasons on Earth.

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The Inner Planets Mars Its Satellites

• The two satellites around Mars were discovered by
  Asaph Hall, an American astronomer, in 1877. He
  continued the tradition by calling these
  satellites after the two sons of the Greek god of
  war, Ares, the counterpart to the Roman god of
  war. Thus, the two satellites are called Phobos,
  which means fear, and Deimos, which means terror.
  
• These two satellites are very tiny objects
  Phobos, which is the inner satellite, is only
  20km high and 28km across, and Deimos, which is
  thus the outer satellite, is actually even
  smaller, being 12km high and 16km across.
• Phobos is so close to Mars that the amount of
  time that it takes to orbit Mars is 7 hours and
  39 minutes, which is actually less time than is
  in a Martian day. Thus, Phobos rises in the west
  and sets in the east, and actually speeds across
  the Martian sky three times every day.
• The amount of time that it takes Deimos to orbit
  Mars is 30 hours and 18 minutes. Deimos passes
  from east to west in the Martian sky, just like
  the moon in Earths sky.
• It is thought that both of Mars satellites were
  originally asteroids that were trapped in orbits
  around Mars by its gravitational pull.

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The Inner Planets Mars Geological Activity 1

• Today, Mars lacks internal heat. This might have
  not always been true, however a region where the
  Marian crust is magnetized in strips of
  alternating polarity was found by the Mars Global
  Surveyor. This same magnetization occurs in the
  oceanic crust on the earth. On Earth, molten rock
  comes to the surface on the ocean bottom and
  spreads out. While it hardens, the geomagnetic
  field is reversing itself periodically, and thus
  the backand-forth magnetic directions are locked
  into the rock. On Mars, the magnetized strips are
  about 200km wide and as much as 2000km long. One
  conclusion from this is that, even though Mars
  doesnt have a magnetic field now, it must have
  once had a strong magnetic field that originated
  from a liquid iron core by the core reversing
  itself a number of times. Also, even though the
  surface of Mars consists of an unbroken shell of
  rock now, there must have been large-scale
  tectonic movements in the past. Thus, during the
  first half-billion years, the interior of Mars
  must have been sufficiently hot to support both a
  magnetic dynamo and plate-tectonic surface
  movement. About 4 billion years ago, this dynamo
  seems to have faded away, and thus new crush
  stopped being formed.

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The Inner Planets Mars Geological Activity 2

• Mars has not been geologically dead since these
  early events, however. The surface of Mars has
  many interesting features, so that seem to have
  been made recently.
• The landscape of Mars is extremely varied There
  are vast plains that are pitted with impact
  crates there are regions that are broken up into
  irregular short ridges and depressions there is
  a canyon as long as the distance from New York
  City to Los Angeles there are deserts of
  windblown sand, and there are extinct volcanoes.
  Some of these volcanoes are not very old, and one
  of them is actually three times the height of
  Mount Everest.

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The Inner Planets Mars Water

• There is evidence to suggest that there was
  running water in the past on Mars. Spacecraft
  have sent back pictures of what appear to be
  dried-up river channels and drainage basins,
  dried-up lack beds, and structures that look like
  sedimentary deposits. Thus, it is quite possible
  that there were seas and oceans on Mars. But,
  since there are undisturbed meteoroid craters in
  areas that show signs of earlier carving by
  running water, at some point, the water must have
  stopped flowing. The number of these craters
  suggest that no large-scale erosion has taken
  place on Mars for probably billions of years.
• In the past, Mars should have been the same as it
  is now (i.e. cold and dry), and thus it was a
  mystery how warm and wet periods have occurred
  thought the history of Mars. It was discovered
  that the Marian river valleys and the craters
  made by impacts of giant asteroids are about the
  same age. For an asteroid of rock and ice that is
  100 to 200 km across, the amount of kinetic
  energy that it has is enough to have heated the
  surface of Mars. This would have thus caused the
  ice in the asteroid to become scalding rain that
  would fall for many years. This rain would have
  led to flash floods, and would have fed the
  streams that carved the valleys that are seen
  today. Any frozen groundwater would have also
  melted and come to the surface. After a few
  thousand years, Mars would have cooled down, and
  the water would have thus turned to ice. There is
  evidence of 25 such impacts that occurred 3.5
  billion years ago, each occurring 10 to 20
  million years apart.

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The Inner Planets Mars Life? 1

• If there is life on Mars, it is adapted to an
  environment that would soon destroy most
  organisms on Earth.
• The climates on Mars are severe by our standards.
  
• Since Mars is over twice as far from the sun as
  the earth is, it receives less solar energy per
  m2 than the earth does.
• The atmosphere of Mars is largely composed of
  carbon dioxide, and it is extremely thin. It is
  actually equivalent to the earths atmosphere at
  an altitude of nearly 40km. Because it is so
  thin, only a little amount of heat from the sun
  is retained after nightfall. This thin atmosphere
  is also unable to screen out harmful solar
  ultraviolet radiation.
• In the summer, at the equator, the daytime
  temperatures rise to over 0C, but the nighttime
  temperatures can be as low as -23C. The average
  surface temperature of the entire planet is about
  -55C.
• There is non-liquid water present on Mars there
  are traces of water vapor in the atmosphere and
  there is much more frozen, some in the ice caps
  of Mars polar regions, and some mixed with
  subsurface soil. There has been liquid water on
  Mars, as was mentioned before, but it is no
  longer present.

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The Inner Planets Mars Life? 2

• The Mars Global Surveyor has shown that there are
  many gullies present on Mars, gullies whose form
  are exactly like the form of gullies on Earth
  that were cut by water gushing out of hillsides.
  A typical gully on Mars is 2m deep, and a few
  hundred meters long. It has a collapsed area on
  top where the water emerged, with an apron of
  debris below. The most surprising aspect of these
  gullies is that they appear to be geologically
  fresh, meaning that they could have been formed
  perhaps a millions years ago, perhaps 10
  thousand, perhaps yesterday, as one scientist
  remarked. The water that gushed out of the
  hillside would have soon evaporated, but not
  before creating the gullies. Some scientist think
  that this water came from deposits of underground
  ice that melted somehow, and others think that it
  might just be from melting snow.

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The Inner Planets Mars Life? 3

• Even though Mars lacks what most terrestrial life
  requires (i.e. a regular supply of liquid water,
  a regular supply of oxygen, and protection from
  solar ultraviolet radiation), it does not mean
  that life of some kind does not exist on Mars.
  Certain bacteria on the earth do not need oxygen,
  so an atmosphere that contains oxygen is not
  indispensable, at least for primitive forms of
  life. Also, some organisms could have evolved on
  Mars to thrive on traces of water gleaned from
  the minerals in surface rocks. In addition, there
  might be shells of some kind around Martian life
  to protect them from ultraviolet radiation. Or
  maybe life on Mars exists underground, with the
  source of energy being heat from the interior,
  rather than sunlight.
• Because the conditions on Mars long ago might
  have been comparable to the conditions on Earth
  from time to time, life of some kind could have
  come into being on Mars. Since the loss of most
  of the carbon dioxide in its atmosphere, which is
  so vital for the greenhouse effect, and the
  disappearance of its surface water, with some
  ending up frozen underground, were gradual, it is
  possible that living things on Mars could have
  adapted to the progressively harsher environment,
  and thus could have survived in some form to the
  present.

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The Inner Planets Mars Looking for Life

• The fact that there is no evidence for life in
  the photographs that are taken well above the
  surface of Mars means nothing. At such a far
  distance, terrestrial life would probably not
  even be visible.
• In 1976, when two spacecraft landed on Mars, one
  of their many tasks was some sensitive
  experiments that are able to detect life in soil.
  These experiments showed no evidence for life on
  Mars now and also no evidence for life on Mars in
  the past. The soil actually turned out to be
  self-sterilizing, which means that solar
  ultraviolet radiation turns the soil minerals
  into strong oxidizing agents that quickly destroy
  organic compounds. These experiments were not
  conclusive, however, since they were limited to
  the two landing sites on the surface. And
  actually some elements that are essential for
  life, such as nitrogen and phosphorous, were
  found. Thus, with the evidence obtained so far,
  it can be said that conditions suitable for life
  possibly existed at one time on the surface of
  Mars, when it was warm and wet, and might sill
  possibly exist today, although it is much less
  probable.
• In 2013, a round-trip mission is scheduled to
  bring back samples of rocks from Mars, which will
  continue the search for the signs of life, both
  past and present, on Mars.