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The Terrestrial Planets
Chapter 4
Section 3
ISN p. 47
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.
– My Very Excellent Mother Just Served Us Nachos OR My
– 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.
• 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 Mercury’s
yrs., 3 of Mercury’s days have passed.
Mercury’s 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?
Mercury’s 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.
– Mercury’s surface is covered
with craters and plains. The
plains of Mercury’s surface are
smooth and relatively crater free.
– Mercury has a planet wide
system of cliffs, called scarps,
that may have developed as
Mercury’s crust shrank and
fractured early in the planet’s
geological history.
Mercury’s Interior
– The high density of Mercury suggests that it has an extensive
nickel-iron core, filling about 42% of Mercury’s volume.
– The detectable magnetic field suggests that Mercury has a
molten zone in its interior.
– Mercury’s small size, high density, and probable molten
interior zone resemble what Earth might be like if its crust
and mantle were removed.
• Venus, the 2nd planet
from the Sun, has no
• Venus’s high albedo and
its proximity to Earth
make it the brightest
planet in Earth’s
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.
Venus’s Atmosphere
– Venus is the hottest planet in
the solar system with an
average surface temperature
of about 737 K (464°C).
– 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.
Venus’s 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?
Venus’s 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 Venus’s slow
rotation rate.
• Earth, the 3rd planet from the
Sun, has many unique
– 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
– Liquid water is required
for life.
– Earth’s moderately dense
atmosphere (78 percent
nitrogen and 21 percent
oxygen) and a mild
greenhouse effect support
conditions suitable for life.
Earth’s Wobble
– Earth’s axis is tilted and has a wobble.
– Precession is the wobble in Earth’s rotational axis.
– It takes Earth’s rotational axis about 26 000 years to go
through one cycle of precession.
– The sideways pull that causes precession comes from the
Moon’s gravitational
force on Earth, as well
as to a lesser extent,
the Sun’s gravitational
• 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
Mars’ Atmosphere
– The composition of Mars’s
atmosphere is similar to
Venus’s atmosphere, but with
much lower density
and pressure.
– The thin atmosphere
creates a constant wind on
– Martian dust storms may
last for weeks at a time.
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
– The Martian surface contains erosional features that
suggest that liquid water once existed on the surface of
– 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.
Mars’ Interior
– Astronomers are
unsure about the
internal structure of
– It is thought to have a
core of iron and nickel,
and possibly sulfur
which is covered by a
– 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.