Download ES Chapter 29

Overview of Our Solar System
Objectives
• Describe early models of our solar system.
• Examine the modern heliocentric model of our
solar system.
• Relate gravity to the motions of celestial bodies.
Vocabulary
– retrograde motion
– aphelion
– astronomical unit
– eccentricity
– perihelion
Overview of Our Solar System
Overview of Our Solar System
• Earth is one of nine planets revolving around, or
orbiting, the Sun.
• All the planets, as well as most of their moons,
also called satellites, orbit the Sun in the same
direction, and all their orbits, except Pluto’s, lie
near the same plane.
• The planets of our solar system have various
sizes, surface conditions, and internal structures.
Overview of Our Solar System
Early Ideas
• When viewed from Earth, the planets slowly
change position each night relative to the position
of the stars.
• Ancient astronomers assumed that the Sun,
planets, and stars orbited a stationary Earth in
what is now known as a geocentric model,
meaning “Earth centered.”
Overview of Our Solar System
Early Ideas
• Some aspects of planetary motion were difficult to
explain with a geocentric model.
– The normal direction of motion for all planets, as
observed from Earth, is toward the east.
– Retrograde motion is when a planet
occasionally will move toward the west across
the sky.
Overview of Our Solar System
Early Ideas
• In 1543, Polish scientist Nicolaus Copernicus
suggested that the Sun was the center of the
solar system.
– In a Sun-centered, or heliocentric, model, the inner
planets move faster in their orbits than the outer
planets do.
– As Earth bypasses a slower-moving outer planet, it
appears that the outer planet temporarily moves
backward in the sky.
Overview of Our Solar System
Early Ideas
Mars appears to
move from east to
west (positions 3
and 4) for a short
time during its
retrograde motion.
Retrograde motion
is similar to passing
a slower car in the
freeway. It appears
that the slower car
is moving backward
relative to the
background.
(not to scale)
Overview of Our Solar System
Early Ideas
Kepler’s First Law
– From 1576–1601, Danish astronomer Tycho Brahe
made accurate observations of planetary positions.
– Using Brahe’s data, Johannes Kepler demonstrated his
first law which states that each planet orbits the Sun in a
shape called an ellipse.
– An ellipse is an oval shape that is centered on two points
called the foci instead of a single point, as in a circle.
Overview of Our Solar System
Early Ideas
Kepler’s First Law
– The major axis, the maximum diameter of the ellipse, is
the line that runs through both foci, one of which is
always the Sun.
– Half of the length
of the major axis is
called the
semimajor axis
and is equal to the
average distance
between the Sun
and the planet.
Overview of Our Solar System
Early Ideas
Kepler’s First Law
– An astronomical unit (AU), 1.496 × 108 km, is the
average distance between the Sun and Earth.
– The average distances between the Sun and each
planet are measured in astronomical units.
Overview of Our Solar System
Early Ideas
Eccentricity
– A planet in an elliptical orbit is not at a constant distance
from the Sun.
• Perihelion is when a planet is at the closest point to
the Sun in its orbit.
• Aphelion is when a planet is farthest point from
from the Sun during its orbit.
Overview of Our Solar System
Early Ideas
Eccentricity
– Eccentricity, which is the ratio of the distance between
the foci to the length of the major axis, defines the shape
of a planet’s elliptical orbit.
– The orbital period is the length of time it takes for a
planet or other body to travel a complete elliptical orbit
around the Sun.
Overview of Our Solar System
Early Ideas
Kepler’s Second and Third Laws
– Kepler’s second law states that because a planet moves
fastest when close to the Sun and slowest when far from
the Sun, equal areas
are swept out in equal
amount of time.
Overview of Our Solar System
Early Ideas
Kepler’s Second and Third Laws
– Kepler also found that the square of the orbital period (P)
equals the cube of the semimajor axis of the orbital
ellipse (a).
– Kepler’s third law states P 2 = a 3, where P is a unit of
time measured in Earth years, and a is a unit of length
measured in astronomical units.
– Italian scientist Galileo Galilei proved, by discovering
four moons orbiting the planet Jupiter, that not all
celestial bodies orbit Earth, and therefore, Earth is not
necessarily the center of the solar system.
Overview of Our Solar System
Early Ideas
Kepler’s Second and Third Laws
– In 1684, English scientist Isaac Newton published a
mathematical and physical explanation of the motions
of celestial bodies.
– Newton’s concepts included the law of universal
gravitation, which provided an explanation of how the
Sun governs the motions of the planets.
Overview of Our Solar System
Gravity and Orbits
• Through observations, Newton realized that any
two bodies attract each other with a force that
depends on their masses and the distance
between the two bodies.
• The force grows stronger in proportion to the
product of the two masses, but diminishes as the
square of the distance between them increases.
Overview of Our Solar System
Gravity and Orbits
Gravity
– Newton’s law of universal gravitation states that every
pair of bodies in the universe attract each other with a
force that is proportional to the product of their masses
and inversely proportional to the square of the distance
between them.
Overview of Our Solar System
Gravity and Orbits
Center of Mass
– Newton also determined that each planet orbits a point
between it and the Sun called the center of mass.
– The center of mass is the balance point between two
orbiting bodies.
– If one of two bodies
orbiting each other is
more massive than the
other, the center of
mass is closer to the
more massive body.
Overview of Our Solar System
Section Assessment
1. Match the following terms with their definitions.
___
D retrograde motion
___
B astronomical unit
___
A perihelion
___
C aphelion
A. the closest point to the center
of mass in an elliptical orbit
B. a distance equal to the
average distance between
Earth and the Sun
C. the farthest point from
the center of mass in an
elliptical orbit
D. when a plant moves east to
west across the sky
Overview of Our Solar System
Section Assessment
2. What is eccentricity?
Eccentricity, which is the ratio of the distance
between the foci to the length of the major axis,
defines the shape of a planet’s orbit.
Overview of Our Solar System
Section Assessment
3. Identify whether the following statements are
true or false.
______
false If the distance between the Moon and Earth
was greater, the gravitational force would be
greater as well.
______
true The center of mass between a plant and the
Sun can be within the Sun.
______
true Planets move faster when they near the
perihelion of their orbit.
______
true Galileo proved that not all celestial bodies
orbit Earth.
The Terrestrial Planets
Objectives
• Describe the properties of the terrestrial planets.
• Compare Earth with the other terrestrial planets.
Vocabulary
– terrestrial planet
– gas giant planet
– precession
The Terrestrial Planets
The Terrestrial Planets
• The nine planets of our solar system can be
grouped into two main categories according to
their basic properties.
– 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.
– 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.
The Terrestrial Planets
Mercury
• Mercury is the closest planet to the Sun and has
no moons.
• Mercury is about one-third the size of Earth
and has a smaller mass and radius.
• Mercury has a slow spin of 1407.6 hours; in
two of Mercury’s years, three of Mercury’s days
have passed.
The Terrestrial Planets
Mercury
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).
The Terrestrial Planets
Mercury
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 planetwide system of cliffs, called
scarps, that may have developed as Mercury’s crust
shrank and fractured early in the planet’s geological
history.
The Terrestrial Planets
Mercury
Interior
– The high density of Mercury suggests that it has an
extensive nickel-iron core, filling about 42 percent 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.
The Terrestrial Planets
Venus
• Venus, the second planet
from the Sun, has no moons.
• 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 counterclockwise with one day equaling
243 Earth days.
• Venus has been explored by radar and
spacecraft.
The Terrestrial Planets
Venus
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.
The Terrestrial Planets
Venus
Surface
– The 1989 Magellan missions of the United States 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.
The Terrestrial Planets
Venus
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.
The Terrestrial Planets
Earth
• Earth, the third 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 three
states: solid, liquid, and gas.
– 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.
The Terrestrial Planets
Earth
Precession
– 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 force.
The Terrestrial Planets
Earth
Precession
The Terrestrial Planets
Mars
• Mars is the fourth 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.
The Terrestrial Planets
Mars
Atmosphere
– The composition of Mars’s atmosphere is similar to
Venus’s atmosphere, but with much lower density
and pressure.
– The thin atmosphere is
turbulent, which creates a
constant wind on Mars.
– Martian dust storms may last
for weeks at a time.
The Terrestrial Planets
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, are
located in the northern hemisphere near a region called
the Tharsis Plateau.
– An enormous canyon, Valles Marineris lies on the
Martian equator and splits the Tharsis Plateau.
The Terrestrial Planets
Mars
Surface
– 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.
The Terrestrial Planets
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.
The Terrestrial Planets
Section Assessment
1. Which planet is physically the most similar to
Earth? In what ways?
Venus is the planet most similar to Earth in
physical properties such as diameter, mass,
and density.
The Terrestrial Planets
Section Assessment
2. Why doesn’t Mars have an efficient greenhouse
effect even though its atmosphere is similar in
composition to Venus?
While Mars and Venus do have similar
atmospheric composition, the density and
pressure of the Martian atmosphere is
much lower.
The Terrestrial Planets
Section Assessment
3. Identify whether the following statements are
true or false.
______
true The largest volcano in the solar system is
located on Mars.
______
false Mercury has one small moon.
______
true The surface of Venus is hot enough to melt lead.
______
false In 26 000 years, the Earth’s axis will point toward
the star Vega.
______
true Earth is the only known tectonically active planet
among the terrestrial planets.
The Gas Giant Planets
Objectives
• Describe the properties of the gas giant planets.
• Identify the unique nature of the planet Pluto.
Vocabulary
– liquid metallic hydrogen
– belt
– zone
The Gas Giant Planets
The Gas Giant Planets
• The interiors of the gas giant planets are
composed of fluids, either gaseous or liquid, and
possibly small, solid cores.
• They are composed primarily of lightweight
elements such as hydrogen, helium, carbon,
nitrogen, and oxygen, and they are very cold at
their surfaces.
• The gas giants have many satellites as well as
ring systems, and they are all very large.
The Gas Giant Planets
Jupiter
• Jupiter is the largest planet, making
up 70 percent of all planetary
matter in our solar system, and
the fifth planet from the Sun.
• Jupiter has a banded appearance as a result
of flow patterns in its atmosphere.
• Jupiter has four major satellites in addition to at
least 12 smaller ones.
• Jupiter has been explored by several United
States space probes which detected volcanic
activity on Jupiter’s closest major moon, Io.
The Gas Giant Planets
Jupiter
Atmosphere
– Jupiter has a low density, 1326 kg/m3, for its huge size
because it is composed of lightweight elements.
– Hydrogen and helium make up the
majority of Jupiter’s atmospheric gas.
– Below the liquid hydrogen, there is
a layer of liquid metallic hydrogen.
– Liquid metallic hydrogen is a
form of hydrogen that has
properties of both a liquid and a
metal, which can exist only under
conditions of very high pressure.
The Gas Giant Planets
Jupiter
Atmosphere
– Electric currents flow within the layer of liquid metallic
hydrogen and generate Jupiter’s magnetic field.
– At less than 10 hours, Jupiter has the shortest day in
the solar system.
– Jupiter’s rapid rotation causes its clouds to flow rapidly
in alternating cloud types called belts and zones.
– Belts are low, warm, dark-colored clouds that sink.
– Zones are high, cool, light-colored clouds that rise.
– Jupiter’s Great Red Spot is a storm that has been
rotating around Jupiter for more than 300 years.
The Gas Giant Planets
Jupiter
Moons and Rings
– Jupiter’s four largest moons, Io, Europa, Ganymede,
and Callisto, are called Galilean satellites.
– Io has been heated by Jupiter’s gravitational force to
the point of becoming almost completely molten inside
and undergoes constant volcanic eruptions.
– Astronomers hypothesize that Europa has a
subsurface ocean of liquid water.
– Jupiter, like the other three gas giant planets,
has rings.
The Gas Giant Planets
Saturn
• Saturn is the sixth planet
from the Sun and the
second-largest planet in
the solar system.
• In 2004, the United States Cassini mission,
launched in 1997, become the fifth probe to visit
the planet.
• It will also release a probe into the atmosphere of
Titan, Saturn’s largest moon, to explore surface
conditions there.
The Gas Giant Planets
Saturn
Atmosphere
– Saturn is not quite as large as Jupiter and has an
average density that is lower than that of water.
– Saturn rotates rapidly for its size
and has flowing belts and zones.
– Saturn’s atmosphere is
dominated by hydrogen
and helium but it also
includes ammonia ice.
The Gas Giant Planets
Saturn
Atmosphere
– The internal structure of Saturn is most likely fluid
throughout with a small, solid core.
– Saturn’s strong magnetic field is aligned with its
rotational axis, which is unusual among the planets.
The Gas Giant Planets
Saturn
Moons and Rings
– Saturn’s ring system has much broader and brighter
rings than those of the other gas giant planets.
– There are seven major rings composed of narrower
rings, called ringlets, and many open gaps.
– The rings are less than 200 m thick, and are aligned
with Saturn’s equatorial plane.
– The ring particles are probably debris left over when
a moon was destroyed either by a collision or
Saturn’s gravity.
The Gas Giant Planets
Saturn
Moons and Rings
– The 18 known satellites of Saturn include the giant
Titan, seven intermediate-sized moons, and a number
of small moons.
– Titan is larger than Earth’s moon, and its atmosphere is
made of nitrogen and methane.
The Gas Giant Planets
Uranus
• The seventh planet from the
Sun, Uranus, was discovered
accidentally in 1781.
• Two of Uranus’s larger moons,
Titania and Oberon, were
discovered in 1787.
• Uranus has at least 18 moons and 10 rings.
• In 1986, the United States Voyager 2 mission
visited Uranus.
The Gas Giant Planets
Uranus
Atmosphere
– Uranus is 4 times as large and 15 times as massive as
Earth and has a blue, velvety appearance.
– Uranus’s atmosphere is
composed of helium and
hydrogen and methane gas
and has no distinct belts
or zones.
– Its internal structure is
completely fluid except for
a small, solid core and
it has a strong magnetic field.
The Gas Giant Planets
Uranus
Atmosphere
– The rotational axis of Uranus is tipped over so far that
the north pole almost lies in its orbital plane.
– Uranus’s atmosphere keeps the planet at a
temperature of 58 K (–215°C).
The Gas Giant Planets
Uranus
Moons and Rings
– The known moons and rings of Uranus orbit in the
planet’s equatorial plane.
– New moons are frequently being discovered causing
frequent changes in the count.
– Uranus’s rings are very dark—almost black.
The Gas Giant Planets
Neptune
• The existence of Neptune
was predicted, based on
small deviations in the
motion of Uranus, before
it was discovered.
• In 1846, Neptune was discovered where
astronomers had predicted it.
• The Voyager 2 probe flew past Neptune in 1989.
The Gas Giant Planets
Neptune
Atmosphere
– Neptune is slightly smaller and denser than Uranus,
but it is still about four times as large as Earth.
– Other similarities between
Neptune and Uranus include
their bluish color, atmospheric
compositions, temperatures,
magnetic fields, interiors,
and particle belts.
– Neptune does have distinctive
clouds and atmospheric belts
and zones similar to those of
Jupiter and Saturn.
The Gas Giant Planets
Neptune
Moons and Rings
– Neptune has many moons, the largest being Triton.
– Triton has a retrograde orbit, which means that it orbits
backward, unlike virtually every other large satellite in
the solar system.
– Triton also has a thin atmosphere and nitrogen geysers.
– Neptune has six rings that are composed of
microscopic-sized dust particles.
The Gas Giant Planets
Pluto
• Pluto, the ninth planet in our solar system, was
discovered in 1930.
• Pluto is very different from the other eight planets
of our solar system and does not fit into either the
terrestrial group or gas giant group.
• The density of Pluto indicates that it is made of
half ice and half rock, and it is smaller than
Earth’s moon.
• The atmosphere is composed of methane and
nitrogen, but in unknown quantities.
The Gas Giant Planets
Pluto
• The orbit of Pluto is so eccentric that at aphelion,
it is 50 AU from the Sun, and at perihelion, it is
almost 30 AU from the Sun.
• Pluto’s rotational axis is tipped so far over that its
north pole actually points south of its orbital plane.
• Pluto’s satellite, Charon, orbits in synchronous
rotation at Pluto’s equatorial plane.
• Many of Pluto’s properties are more similar to
those of the gas giants’ large moons than they are
to those of any other planet.
The Gas Giant Planets
Section Assessment
1. What is liquid metallic hydrogen?
Liquid metallic hydrogen is a form of hydrogen
that has properties of both a liquid and a metal,
which can exist only under conditions of very
high pressure.
The Gas Giant Planets
Section Assessment
2. Number the nine planets, starting with the
closest to the Sun.
___
7 Uranus
___
6 Saturn
___
4 Mars
___
9 Pluto
___
1 Mercury
___
8 Neptune
___
5 Jupiter
___
2 Venus
___
3 Earth
The Gas Giant Planets
Section Assessment
3. Identify whether the following statements are
true or false.
______
false Saturn’s rings are about 200 km thick.
______
false Earth’s Moon is largest satellite in our
solar system.
______
true Jupiter’s Great Red Spot is a storm that has been
ongoing for more than 300 years.
______
false Jupiter makes up about 40 percent of all
planetary matter in our solar system.
Formation of Our Solar System
Objectives
• Summarize the properties of the solar system that
support the theory of the solar system’s formation.
• Describe how the planets formed from a disk
surrounding the young Sun.
• Explore remnants of solar system formation.
Vocabulary
– planetesimal
– meteor
– coma
– asteroid
– meteorite
– nucleus
– meteoroid
– comet
– meteor shower
Formation of Our Solar System
Formation of Our Solar System
• Astronomers use Earth-based observations and
data from probes to derive theories about how
our solar system formed.
• The significant observations related to our solar
system’s formation include the shape of our
solar system, the differences among the planets,
and the oldest planetary surfaces, asteroids,
meteorites, and comets.
Formation of Our Solar System
A Collapsing Interstellar Cloud
• Stars and planets form from clouds of gas and
dust, called interstellar clouds, which exist in
space between the stars.
• The interstellar clouds consist mostly of gas,
especially hydrogen and helium that often
appear as blotches of light and dark.
• Many interstellar clouds can be observed along
the Milky Way in regions that have relatively high
concentrations of interstellar gas and dust.
Formation of Our Solar System
A Collapsing Interstellar Cloud
• Our solar system may have begun when
interstellar gas started to condense as a result of
gravity and became concentrated enough to
form the Sun and planets.
– The collapse is initially slow, but it accelerates and the
cloud soon becomes much denser at its center.
– Rotation slows the collapse in the equatorial plane,
and the cloud becomes flattened.
– The cloud eventually becomes a rotating disk with a
dense concentration at the center.
Formation of Our Solar System
Sun and Planet Formation
• The disk of dust and gas that formed the Sun and
planets is known as the solar nebula.
• The dense concentration of gas at the center of
this rotating disk eventually became the Sun.
• In the disk surrounding the Sun, the temperature
varied greatly with location.
• As the disk began to cool, different elements and
compounds were able to condense depending
on their distance from the Sun which impacted
the compositions of the forming planets.
Formation of Our Solar System
Sun and Planet Formation
Elements and
compounds that were
able to condense close
to the Sun, where it was
warm, are called
refractory elements,
and far from the Sun,
where it was cool,
volatile elements could
condense. Refractory
elements, such as iron,
comprise the terrestrial
planets, which are close
to the Sun. Volatile
elements, such as ices
and gases like
hydrogen, comprise the
planets further from the
Sun, where it is cool.
Formation of Our Solar System
Sun and Planet Formation
The Growth of Objects
– Once the condensing slowed, the tiny grains of
condensed material started to accumulate and merge
together to form larger bodies.
– Planetesimals are the solid bodies, reaching hundreds
of kilometers in diameter, that formed as smaller
particles collided and stuck together.
– Further growth continued through collisions and
mergers of planetesimals resulting in a smaller number
of larger bodies: the planets.
Formation of Our Solar System
Sun and Planet Formation
Merging into Planets
– Jupiter was the first large planet to develop in the outer
solar system.
– As its size increased, its gravity began to attract
additional gas, dust, and planetesimals.
– As each gas giant acquired material from its
surroundings, a disk formed in its equatorial plane,
much like the disk of the early solar system.
– In the disk, matter coalesced to form satellites.
Formation of Our Solar System
Sun and Planet Formation
Merging into Planets
– The inner planets also formed by the merging of
planetesimals.
– These planetesimals were composed primarily of
refractory elements, so the inner planets are rocky
and dense.
– The Sun’s gravitational force is theorized to have
swept up much of the gas in the area of the inner
planets, preventing them from acquiring much
additional material.
– The inner planets initially ended up with no satellites.
Formation of Our Solar System
Sun and Planet Formation
Debris
– The amount of interplanetary debris thinned out as it
crashed into planets or was diverted out of the solar
system.
– The planetesimals in the area between Jupiter and
Mars, known as the asteroid belt, remained there
because Jupiter’s gravitational force prevented them
from merging to form a planet.
Formation of Our Solar System
Asteroids
• Asteroids comprise the thousands and thousands
of bodies that orbit the Sun within the planetary
orbits that are leftovers from the formation of the
solar system.
• Asteroids range from a few kilometers to about
1000 km in diameter and have pitted, irregular
surfaces.
• Most asteroids are located between the orbits of
Mars and Jupiter within the asteroid belt.
Formation of Our Solar System
Asteroids
Pieces of Asteroids
– As the asteroids orbit, they occasionally collide and
break into fragments.
• A meteoroid is a asteroid fragment or any other
interplanetary material that falls toward Earth and
enters Earth’s atmosphere.
• A meteor is the streak of light produced when a
meteoroid burns up in Earth’s atmosphere.
• A meteorite is part of a meteoroid, that does not
completely burn up, that collides with the ground.
Formation of Our Solar System
Comets
• Comets are small, icy bodies that have highly
eccentric orbits around the Sun and are remnants
from solar system formation.
• Comets are made of ice and rock, and they
range from 1 to 10 km in diameter.
• There are two clusters, or clouds, of comets: the
Kuiper belt and the Oort cloud.
• Occasionally, a comet is disturbed by the gravity
of another object and is thrown into the inner
solar system from one of these clusters.
Formation of Our Solar System
Comets
The Orbits of Comets
– When a comet nears the sun in its highly eccentric orbit,
it begins to evaporate and form a head and one or
more tails.
– The coma is an extended
volume of glowing gas
flowing from a comet’s head.
– The nucleus of a comet is the
small solid core that releases
gases and dust particles that
form the coma and tails when
it is heated.
Formation of Our Solar System
Comets
Periodic Comets
– Comets that repeatedly orbit into the inner solar system
are known as periodic comets.
– Meteor showers occur when Earth intersects a
cometary orbit and numerous particles from the comet
burn up upon entering Earth’s upper atmosphere.
– Most meteors are caused by dust particles from
comets, while most meteorites, the solid chunks of rock
or metal that reach Earth’s surface, are fragments of
asteroids.
Formation of Our Solar System
Section Assessment
1. Match the following terms with their definitions.
___
A asteroid
___
C comet
___
B meteor
___
D meteorite
A. small rocky bodies orbiting the
Sun that are most likely leftover
planetesimals.
B. the streak of light produced
when interplanetary material
burns up upon entering Earth’s
atmosphere
C. small, icy bodies that have
highly eccentric orbits around
the Sun
D. interplanetary material that
impacts Earth’s surface
Formation of Our Solar System
Section Assessment
2. What are planetesimals and what is their role in
forming planets?
Planetesimals are objects that formed in the early
solar system through collisions among particle
grains and grew to hundreds of kilometers in
diameter. Collisions and mergers among
planetesimals eventually led to fewer but larger
bodies: the planets.
Formation of Our Solar System
Section Assessment
3. Identify whether the following statements are
true or false.
______
true Temperature variation in the solar nebula
determined the primary elements in the planets.
______
false All comet tails point toward the Sun.
______
false The gravitational pull of Saturn has prevented
the material in the asteroid belt from forming
another planet.
______
true The inner planets initially had no satellites.
Chapter Resources Menu
Study Guide
Section 29.1
Section 29.2
Section 29.3
Section 29.4
Chapter Assessment
Image Bank
Section 29.1 Study Guide
Section 29.1 Main Ideas
• Early astronomers explained the motions of the planets
with geocentric models, including epicycles.
• Copernicus, Brahe, Kepler, and Galileo developed
evidence supporting a heliocentric solar system model.
• Newton developed a law of gravitation that was used to
demonstrate the validity of the heliocentric model.
Section 29.2 Study Guide
Section 29.2 Main Ideas
• The terrestrial planets include the four planets closest to
the Sun. They are relatively small and dense, and they
have rocky surfaces.
• Mercury has a surface similar to the Moon’s, but a very
different interior.
• Venus has an extremely hot surface as a result of
greenhouse heating, but is similar to Earth in other
properties.
• Earth is suitable for life because of its unique orbital
position that allows water to exist in all three phases on
the surface.
• Mars shows signs of having once had tectonic activity.
Section 29.3 Study Guide
Section 29.3 Main Ideas
• The gas giant planets are very large and have low
densities, no solid surfaces, ring systems, and
many moons.
• Jupiter is the largest of the planets. It has a fluid interior,
except for a small rocky core, and several moons. Saturn
is slightly smaller than Jupiter and has a more extensive
ring system.
• Uranus and Neptune are very similar in size and
composition.
• Pluto is not classified as a gas giant or a terrestrial planet.
Section 29.4 Study Guide
Section 29.4 Main Ideas
• The solar system formed from a collapsing interstellar
cloud that flattened into a disk from which the planets
formed.
• Terrestrial planets formed from refractory materials in the
hot inner disk, and gas giants formed from volatile
elements in the cold outer disk.
• Asteroids are rocky remnants of the early solar system.
Most of them orbit the Sun between Mars and Jupiter.
• Comets have highly eccentric orbits and are made of rock
and ice. When they are close to the Sun, they glow brightly
and have a head and tails of gas and dust.
Chapter Assessment
Multiple Choice
1. When a planet is at its farthest point from the Sun
in its orbit, it is at ____.
a. perihelion
c. eccentricity
b. aphelion
d. its foci
If a planet is at perihelion it is at its closest point to the
sun. Eccentricity defines the shape of a planet’s elliptical
orbit. Foci are the two points that an elliptical orbit is
centered on.
Chapter Assessment
Multiple Choice
2. Which planet has the hottest surface
temperature?
a. Mars
c. Earth
b. Venus
d. Mercury
Although Mercury is closer to the Sun than Venus, Venus
has the highest surface temperature of any planet in our
solar system due to a very efficient greenhouse effect.
The average surface temperature on Venus is about 737
K (464ºC) which is hot enough to melt lead.
Chapter Assessment
Multiple Choice
3. Which planet does not fit into either major
category of planets?
a. Mercury
c. Pluto
b. Jupiter
d. Earth
Pluto does not fit the characteristics of either a terrestrial
planet or a gas giant planet. One theory suggests that it
was once a satellite of Neptune that escaped as a result
of a near-collision with Triton, Neptune’s largest satellite.
Chapter Assessment
Multiple Choice
4. Which of the following is usually responsible for
meteor showers?
a. asteroids
c. planetesimals
b. meteorites
d. comets
When Earth intersects a cometary orbit, we experience a
meteor shower as particles from the comet burn up upon
entering Earth’s atmosphere. Most meteors are caused
by dust particles from comets, while most meteorites, the
solid chunks of rock or metal that reach Earth’s surface.
are fragments of asteroids.
Chapter Assessment
Multiple Choice
5. What unit of distance is used to measure
distance in our solar system?
a. kilometers
c. astronomical units
b. light years
d. gravitational force
One astronomical unit (AU) is equal to the average
distance between Earth and the Sun, or 1.496 × 108 km.
The average distance between the Sun and each planet
are measured in astronomical units, and therefore these
distances are relative to Earth’s average distance from
the Sun.
Chapter Assessment
Short Answer
6. What is precession? How will the night
sky change?
Precession is the wobble in Earth’s rotational
axis. Once cycle of precession takes 26 000
years to complete. Currently, the axis leaving
the north pole points toward the star Polaris.
By approximately 14 000 A.D. the axis will
point toward the star Vega.
Chapter Assessment
Short Answer
7. Why is Jupiter the largest of the gas
giant planets?
Jupiter was the first gas giant planet to form. As
Jupiter increased in size through mergers of icy
planetesimals, its gravity began to attract
additional gas, dust, and planetesimals, causing
Jupiter to grow even larger. The other gas giants
formed in the same way, but could not grow as
large because Jupiter had collected so much of
the material in the vicinity.
Chapter Assessment
True or False
8. Identify whether the following statements are
true or false.
______
false The atmosphere of Mars is similar in
composition to Earth.
______
false Jupiter is the only gas giant planet without rings.
______
true The Oort cloud lies more than 100 000 AU from
the Sun.
______
true Earth is the only planet in the solar system
where water exists in liquid, solid, and gas form.
______
true Jupiter has the shortest day in the solar system.
Image Bank
Chapter 29 Images
Image Bank
Chapter 29 Images
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Chapter 29 Images
Image Bank
Chapter 29 Images
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