Transcript Chapter 29

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
• 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.”
• Some aspects of planetary motion were difficult to
explain and therefore...
• In 1543, Copernicus suggested that the Sun was
the center of the solar system, a heliocentric
Overview of Our Solar System
Gravity and Orbits
– The planets revolve around the sun due to its large
gravitational force.
– The planets move in an elliptical orbit, all in the same
The Terrestrial Planets
The 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 Jovian 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.
Categorizing Planets
• Size is the major difference, but they also differ
in density, chemical make-up and rate of
• The terrestrial planets are smaller, denser, made
of rocky and metallic substances and rotate
slower. They also have less satellites, the most
being two for Mars.
• The Jovian (or outer) planets are larger, have a
rig or rings, are less dense (Jupiter could float
on water!) made of gasses and ice and have
many satellites. Jupiter has 63 satellites!
Educated Earth
The Terrestrial Planets
• Mercury is located closest to the Sun and has no
• Mercury is about one-third the size of Earth
and has a smaller mass and radius.
• A day is actually longer than a year on Mercury
because of its very slow rotation. Mercury has
a slow spin of 1407.6 hours so in two of
Mercury’s years, three of Mercury’s days have
The Terrestrial Planets
– Mercury has essentially
no atmosphere, and what
little does exist is composed
primarily of oxygen and
– The daytime surface
temperature on Mercury
is 700 K (427ºC), while
temperatures at night fall
to 100 K (–173ºC). It is the
largest temperature range.
The Terrestrial Planets
– Most of what we know about Mercury is based on
radio observations and images from a United
States space probe mission in 1974 & 5, called
Mariner 10.
– Mercury’s surface is covered with craters, making it
look similar to the moon.
– The plains are thought to have formed from lava
flows, much like the moon.
The Terrestrial Planets
– 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. It’s possible these
were lost in an early collision.
The Terrestrial Planets
• 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.
• Venus rotates slowly counterclockwise with one
day equaling 243 Earth days.
• It has a retrograde rotation, meaning it rotates
backwards from all the other planets. It may be
due to an early collision.
The Terrestrial Planets
– Venus was studied in 1978 by Pioneer-Venus and in
1989 the Magellan missions 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- our twin!
– Venus is called “Earth’s Twin” because its
size/diameter, mass and density are similar to
Earth. Therefore, the internal structure is most
likely similar.
Venus - temperature and pressure
– Venus is the hottest planet in the solar system,
hot enough to melt lead at 464°C!
– The atmospheric pressure on Venus is 92 Earth
atmospheres, compared to 1 on earth.
The Terrestrial Planets
– The atmosphere is made of
CO2 and Na. Therefore it
has an efficient greenhouse
effect. The clouds will
actually rain sulfuric acid.
There are lots of clouds
which leads to a “Runaway
Greenhouse Effect” making
it the hottest planet.
The Terrestrial Planets
• 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
• Mars is the fourth planet
from the Sun. It is called
the “Red Planet” because
of iron oxide (rust) in the
• Mars is smaller and less
dense than Earth.
• It has two irregularly-shaped moons, Phobos and
Deimos. They are captured asteroids.
Studying Mars
• Missions include Mariner 4, Mariner 9, Mars
Climate Orbiter and the Mars Explorer Rover
Mission in 2003.
• The rovers, Spirit and Opportunity are there still
sending back information.
The Terrestrial Planets
– Atmosphere is made mostly of carbon dioxide. (similar
to Venus)
– 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 has four gigantic shield volcanoes including
Olympus Mons, the largest mountain in the solar
– An enormous canyon, Valles Marineris, more than
4000km long, lies on the Martian equator and splits the
Tharsis Plateau.
The Terrestrial Planets
– Other surface features include dried river and lake beds
and channel runoff. These suggest the existence of
liquid water once on the surface of Mars.
– Mars has ice caps of frozen carbon dioxide covering
both poles that grow and shrink with the seasons on
– Water ice lies beneath the carbon dioxide ice in the
northern cap and we believer there might be liquid
water under the surface of Mars.
The Terrestrial Planets
– 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 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 is 5th from the sun and is the
largest planet. Its diameter is 11
times ours and only 10 times less
than the sun. It makes up 70% of all
matter in our solar system.
• Jupiter has a banded appearance as a result
of flow patterns in its atmosphere.
• It has the Great Red Spot, a giant storm the size
of Earth.
• Jupiter has been explored by 5 U S space probes,
Pioneer 10 and 11, Voyager I and II, and
Spacecraft Galileo.
The Gas Giant Planets
– Jupiter has a low density, it
could actually float on
– Hydrogen and helium make
up the
majority of Jupiter’s
atmospheric gas.
The Gas Giant Planets
– At less than 10 hours, Jupiter has the shortest day in
the solar system.
The Gas Giant Planets
Moons and Rings
• Has 63 moons, at last count. Jupiter’s four largest
moons, Io, Europa, Ganymede, and Callisto, are called
Galilean satellites. Three of these are larger than our
moon and all are larger than Pluto!
• There is volcanic activity on Jupiter’s closest major
moon, Io.
– Europa is believed to possibly have a subsurface
ocean of liquid water.
– Jupiter, like the other three gas giant planets,
has rings.
The Gas Giant Planets
• 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. The other missions were Pioneer 10
and 11 and Voyager I and II.
The Gas Giant Planets
-- Like Jupiter, Saturn rotates rapidly for its size
and has flowing belts.
– Its density and structure are
similar to Jupiter. Saturn has
a small solid core with a large
gaseous outside.
– Saturn’s atmosphere is
dominated by hydrogen
and helium but it also
includes ammonia ice.
– Has magnetic field 1000 times Earth’s
The Gas Giant Planets
Moo ns and Rings
– Saturn’s ring system is the most striking, it 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 ring particles are probably debris left over when
a moon was destroyed either by a collision or
Saturn’s gravity. They are made up of pieces of rock
and ice, from microscopic bits up the size of houses.
The Gas Giant Planets
Moons and Rings
– It now has 31 known satellites
– Titan is the largest, it is larger than Earth’s moon, and
its atmosphere is made of nitrogen and methane.
Methane may exist in three states there as water does
on Earth
The Gas Giant Planets
• 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 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
– 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
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
• 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 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
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, 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
• 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
• 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.
– 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.
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
– 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.
Other Objects in the Solar System
Formation of Our Solar System
– Asteroids are rocky remnants of the early solar
system. Most (95%) are found in the asteroid
belt between Mars and Jupiter.
– These planetesimals remained there because
Jupiter’s gravitational force prevented them from
merging to form a planet.
– From 1 mile diameter up to Ceres that is 584miles in
diameter. One, Ida, even has its own moon. They have
weird, oblong shapes. They can exist as moons of other
planets such as Phobos and Deimos that are moons of
Formation of Our Solar System
Other Objects in the Solar System
– 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.
So a “falling star” or “shooting star” is actually a
• A meteor
shower may
occur when
particles from
a comet burn
up in the
as Earth
intersects a
comet’s orbit.
Meteor Crater
Other Objects in the Solar System
• A meteorite is part of a meteoroid, that does not
completely burn up, that collides with the ground.
Formation of Our Solar System
• Comets are small, icy bodies that have highly
eccentric orbits around the Sun and are remnants
from solar system formation. “Dirty snowballs”
• 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
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
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
Comet Hale-Bopp
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
B. the streak of light produced
when interplanetary material
burns up upon entering Earth’s
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
• 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
• 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
• 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
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.
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