The Terrestrial Planets

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The Terrestrial Planets

• Chapter 4
• Section 3
• ISN p. 47

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The Terrestrial Planets

• The terrestrial planets are the inner four
  planets of Mercury, Venus, Earth, and Mars that
  are close to the size of Earth and have solid,
  rocky surfaces.
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• The gas giant planets are the outer planets of
  Jupiter, Saturn, Uranus, and Neptune which are
  much larger, more gaseous, and lack solid
  surfaces.
• Pluto, the ninth planet from the Sun, has a solid
  surface, but it does not fit into either
  category.

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Mercury

• Mercury is the closest planet to the Sun and has
  no moons.
• Mercury is about 1/3 the size of Earth and has a
  smaller mass and radius.
• Mercury has a slow spin of 1407.6 hours in 2 of
  Mercurys yrs., 3 of Mercurys days have passed.

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Mercurys Atmosphere

• Mercury has essentially no atmosphere, and what
  little does exist is composed primarily of oxygen
  and sodium.
• The daytime surface temperature on Mercury is
  700 K (427ºC), while temperatures at night fall
  to 100 K (173ºC).
• So what do you think the surface is like?

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Mercurys Surface

• Most of what we know about Mercury is based on
  radio observations and images from a United
  States space probe mission, called Mariner 10.
• Mercurys surface is covered with craters and
  plains. The plains of Mercurys surface are
  smooth and relatively crater free.
• Mercury has a planet wide system of cliffs,
  called scarps, that may have developed as
  Mercurys crust shrank and fractured early in the
  planets geological history.

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Mercurys Interior

• The high density of Mercury suggests that it has
  an extensive nickel-iron core, filling about 42
  of Mercurys volume.
• The detectable magnetic field suggests that
  Mercury has a molten zone in its interior.
• Mercurys small size, high density, and probable
  molten interior zone resemble what Earth might be
  like if its crust and mantle were removed.

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Venus

• Venus, the 2nd planet from the Sun, has no moons.
  
• Venuss high albedo and its proximity to Earth
  make it the brightest planet in Earths nighttime
  sky.
• The surface of Venus is very hot, and it rotates
  slowly clockwise with one day equaling 243 Earth
  days.
• Venus has been explored by radar and spacecraft.

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Venuss Atmosphere

• Venus is the hottest planet in the solar system
  with an average surface temperature of about 737
  K (464C).
• The atmospheric pressure on Venus is equivalent
  to 92 Earth atmospheres.
• An efficient greenhouse effect is achieved with
  an atmosphere that is primarily carbon dioxide
  and nitrogen with clouds of sulfuric acid.

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Venuss Surface

• The 1989 Magellan missions of the U.S. used radar
  reflection measurements to map the surface of
  Venus in detail.
• The surface has been smoothed by volcanic lava
  flows, and it has only a few impact craters.
• The most recent global episode of volcanic
  activity took place about 500 million years ago.
• There is little evidence of current tectonic
  activity on Venus, and there is no well-defined
  system of crustal plates.

Why do you think that it appears to be blue in
some photographs?
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Venuss Interior

• The size and density of Venus are similar to
  Earth, so the internal structure is most likely
  similar.
• It is theorized that Venus has a liquid metal
  core that extends halfway to the surface.
• There is no measurable magnetic field despite
  this liquid core, which is probably due to
  Venuss slow rotation rate.

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Earth

• Earth, the 3rd planet from the Sun, has many
  unique properties.
• Its distance from the Sun and its nearly circular
  orbit allow liquid water to exist on its surface
  in all 3 states solid, liquid, and gas.
• Liquid water is required for life.
• Earths moderately dense atmosphere (78 percent
  nitrogen and 21 percent oxygen) and a mild
  greenhouse effect support conditions suitable for
  life.

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Earths Wobble

• Earths axis is tilted and has a wobble.
• Precession is the wobble in Earths rotational
  axis.
• It takes Earths rotational axis about 26 000
  years to go through one cycle of precession.
• The sideways pull that causes precession comes
  from the Moons gravitational
• force on Earth, as well
• as to a lesser extent,
• the Suns gravitational
• force.

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Mars

• Mars is the 4th planet from the Sun and the
  outermost of the terrestrial planets.
• Mars is smaller and less dense than Earth and has
  two irregularly-shaped moons, Phobos and Deimos.
• Mars has been
• explored by
• telescopes on Earth
• and with probes
• beginning in the
• 1960s that have
• flown by, orbited, or
• landed.

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Mars Atmosphere

• The composition of Marss atmosphere is similar
  to Venuss atmosphere, but with much lower
  density and pressure.
• The thin atmosphere creates a constant wind on
  Mars.
• Martian dust storms may last for weeks at a time.
  

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Mars Surface

• The southern hemisphere of Mars is a heavily
  cratered, highland region, while the northern
  hemisphere is dominated by plains that are
  sparsely cratered.
• Four gigantic shield volcanoes including Olympus
  Mons, the largest mountain in the solar system.
• An enormous canyon, Valles Marineris lies on the
  Martian equator.
• The Martian surface contains erosional features
  that suggest that liquid water once existed on
  the surface of Mars.
• Mars has polar ice caps of frozen carbon dioxide
  covering both poles that grow and shrink with the
  seasons on Mars.
• Water ice lies beneath the carbon dioxide ice in
  the northern cap.

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Mars Interior

• Astronomers are unsure about the internal
  structure of Mars.
• It is thought to have a core of iron and nickel,
  and possibly sulfur which is covered by a mantle.
  
• Because Mars has no magnetic field, the core is
  probably solid.
• There is no evidence of current tectonic activity
  or tectonic plates on the surface of the crust.