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The Inner Planets


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Title: The Inner Planets

The Inner Planets
  • 2012

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

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.

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.

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.

  • 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.

  • 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

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.

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.

Solar System
  • There are at least eleven planets (or planet-like
    objects)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!

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.

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!

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.

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

  • 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.

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Mercury Data
  • Closest to the sun.
  • Temperature ranges from 427C in daylight to
    -173C at night. (most extreme range in solar
  • Rotates 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.

Mercury Facts
  • Diameter one third the size of Earth
  • Distance 0.4 AU
  • Atmosphere no atmosphere worth mentioning
  • Features Craters with smooth plains, similar to
    our Moon, and most extreme temperature range in
    solar system
  • Life no life because of lack of atmosphere and
    extreme temperature range

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

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.

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Venus Atmosphere
  • Seen from Earth, Venus is completely cloud
  • 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
  • This is the pressure you would feel if you were
    under 915 meters of water!
  • Crushing Pressure!

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.

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 rotates 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.

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.
  • Like Earth without the water!

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.

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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

Venus Facts
  • Diameter 0.9 Earth
  • Distance 0.7 AU
  • Atmosphere 96 carbon dioxide at almost 100
    atmospheres. Runaway greenhouse effect.
  • Features hottest surface in solar system.
    Retrograde rotation. Evening/Morning Star
  • Life Very doubtful, the pressure and
    temperatures are too high. Sulfuric acid in
    atmosphere does not help either.

Earth Facts
  • Diameter 1 earth
  • Distance 1 AU
  • Atmosphere 78 Nitrogen, 21 Oxygen at 1
  • Features water world, looks like a blue marble
    from space, moderate temperature and pressures
  • Life teeming with life. Planet is just right
    for life as we know it.

  • Mars is the Latin name for Ares, the Greek god of
  • Iron oxide in its soil gives Mars a red
  • Hence the Red Planet!

Mars Atmosphere
  • Mars has an atmosphere that is mainly carbon
  • It is very thin, only 0.01 atmospheres at the
  • 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.

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
  • It is three times taller than Mt. Everest.
  • There are many other volcanoes on Mars, but none
    seem to be active at this time.

Volcano Comparision
  • Heights of Mt. Everest on the Earth, Maxwell
    Montes on Venus and Olympus Mons. (The horizontal
    scale has been drastically squashed.)

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!

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
  • If there was water it is possible that life could
    have existed on Mars, and still might.

Ice Caps
  • The north and south poles of Mars are covered by
    ice caps composed of frozen carbon dioxide and
  • They wax and wane with the seasons.

Mars Data
  • Mars is about half the size of the Earth.
  • A 100 pound sixth grader would weigh 39 pounds on
  • It is very cold on Mars, with the average
    temperature ranging from -140 C to 20 C.

  • Mars has two very small moons, Phobos (fear) and
    Diemos (terror).
  • They are named after the horses that pulled
    Marss chariot.
  • The larger Deimos is only 23-km in diameter.
  • Both appear to be captured asteroids.

Mars Missions
  • There have been many missions to Mars, starting
    with the Viking craft in 1976.
  • There are currently two orbiters and one rover
    collecting data on Mars. While Spirit finally
    stopped responding last year, Opportunity is
    starting its 9th year of operation. Pretty good
    for a planned 90 day mission!
  • Manned missions are also currently being planned,
    around 2025 or so.

  • Diameter 0.5 Earth
  • Distance 1.5 AU
  • Atmosphere 96 carbon dioxide at 0.01
  • Features large canyons, volcanoes. Two moons,
    both are captured asteroids.
  • Ancient dried up lakes, streams, rivers, and
    seas. Called the Red Planet.
  • Life Possibly ancient life when there was liquid
    water on the planet. Could still exist under the