Section 28.4
Other Solar System Objects
Objectives
Distinguish between planets and dwarf planets.
Identify the oldest members of the solar system.
Describe meteoroids, meteors, and meteorites.
Determine the structure and behavior of comets.
Section 28.4
Other Solar System Objects
Rocks, dust, and ice compose the remaining
2 percent of the solar system.
Review Vocabulary
smog: air polluted with hydrocarbons and
nitrogen oxides
Section 28.4
Other Solar System Objects
New Vocabulary
dwarf planet
Kuiper belt
meteoroid
comet
meteor
meteor shower
meteorite
Section 28.4
Other Solar System Objects
Dwarf Planets
In the early 2000s, astronomers began to
detect large objects in the region of the
planet Pluto, about 40 AU from the Sun,
called the Kuiper belt.
• Classification in order of decreasing size
• 1. Planets
• 2. Dwarf planets
• 3. Other solar system objects.
Section 28.4
Other Solar System Objects
Dwarf Planets
In 2003 an object, now known as Eris, was
discovered that appeared to be the same
size, or larger, than Pluto.
At that time, the scientific community began
to take a closer look at the planetary status
of Pluto and other solar system objects.
Section 28.4
Other Solar System Objects
Dwarf Planets
Ceres
In 1801, Giuseppe Piazzi discovered a large
object, which was given the name Ceres, in
orbit between Mars and Jupiter. Ceres is the
largest asteroid. Scientists had predicted that
there was a planet somewhere in that region,
and it seemed that this discovery was it.
However, Ceres was extremely small for a
planet.
Section 28.4
Other Solar System Objects
Dwarf Planets
Ceres
In the century following the discovery of Ceres,
hundreds of thousands of other objects were
discovered in the area between Mars and
Jupiter. Therefore, Ceres was no longer thought
of as a planet, but as the largest of the asteroids
in what would be called the asteroid belt.
Section 28.4
Other Solar System Objects
Dwarf Planets
Pluto
Since its discovery by Clyde Tombaugh in
1930, Pluto has been an unusual planet. It
is not a terrestrial or gas planet; it is made
of rock and ice.
Section 28.4
Other Solar System Objects
Dwarf Planets
Pluto
Pluto has a long, elliptical orbit that overlaps
the orbit of Neptune. It is also smaller than
Earth’s Moon. It has three moons, two of
which orbit at widely odd angles from the
plane of the ecliptic.
Section 28.4
Other Solar System Objects
Dwarf Planets
How many others?
With the discovery of objects close to and
larger than Pluto’s size, the International
Astronomical Union (IAU) chose to create a
new classification of objects in space called
dwarf planets.
Section 28.4
Other Solar System Objects
Dwarf Planets
How many others?
The IAU has defined a dwarf planet as an
object that, due to its own gravity, is spherical
in shape, orbits the Sun, is not a satellite, and
has not cleared the area of its orbit of smaller
debris.
Section 28.4
Other Solar System Objects
Dwarf Planets
How many others?
Currently the IAU has limited the dwarf planet
classification to Pluto, Eris, and Ceres, but
there are at least 12 other objects whose
classifications are undecided.
Section 28.4
Other Solar System Objects
Visualizing the Kuiper Belt
Recent findings of objects beyond Pluto,
in a vast disk called the Kuiper belt,
have forced scientists to rethink what
features define a planet.
Section 28.4
Other Solar System Objects
Small Solar System Bodies
Once the IAU defined planets and dwarf
planets, they had to identify what was left.
In the early 1800s, a name was given to the
1)rocky planetesimals between Mars and
Jupiter— the asteroid belt.
Section 28.4
Other Solar System Objects
Small Solar System Bodies
2)Objects beyond the orbit of Neptune have
been called trans-Neptunian objects, Kuiper
belt objects, comets, and members of the
Oort cloud. The IAU calls all these objects,
collectively, small solar system bodies.
Section 28.4
Other Solar System Objects
Small Solar System Bodies
Asteroids
There are thousands of asteroids orbiting the
Sun between Mars and Jupiter. As asteroids
orbit, they occasionally collide and break into
fragments. When an asteroid fragment, or any
other interplanetary material, enters Earth’s
atmosphere, it is called a meteoroid.
Section 28.4
Other Solar System Objects
Small Solar System Bodies
Asteroids
As a meteoroid passes through the
atmosphere, it is heated by friction and burns,
producing a streak of light called a meteor.
If the meteoroid does not burn up completely
and part of it strikes the ground, the part that
hits the ground is called a meteorite.
Section 28.4
Other Solar System Objects
Small Solar System Bodies
Kuiper belt
The Kuiper belt is a group of small solar
system bodies that are mostly rock and ice.
Most of these bodies probably formed in
this region—30 to 50 AU from the Sun—
from the material left over from the
formation of the Sun and planets.
Section 28.4
Other Solar System Objects
Small Solar System Bodies
Kuiper belt
The Kuiper belt appears as
the outermost limit of the
planetary disk. The Oort
cloud surrounds the Sun,
echoing its solar sphere.
Section 28.4
Other Solar System Objects
Comets
Comets are small, icy bodies that have highly
eccentric orbits around the Sun.
Located in Kuiper belt and Oort cloud.
Ranging from 1 to 10 km in diameter, most
comets orbit in a continuous distribution that
extends from the Kuiper belt to 100,000 AU
from the Sun. The outermost region is known
as the Oort cloud.
Section 28.4
Other Solar System Objects
Comets
Comet structure
When a comet comes within 3 AU of the
Sun, it begins to evaporate and forms a
head and one or more tails. The head is
surrounded by an envelope of glowing gas,
and it has a small solid core.
Section 28.4
Other Solar System Objects
Comets
Comet structure
A comet’s tail always
points away from the
Sun and is driven by
a stream of particles
and radiation.
Section 28.4
Other Solar System Objects
Comets
Periodic comets
Comets that repeatedly return to the inner
solar system are known as periodic comets.
Each time a periodic comet comes near the
Sun, it loses some of its matter, leaving
behind a trail of particles.
Section 28.4
Other Solar System Objects
Comets
Periodic comets
When Earth crosses the trail of a comet,
particles left in the trail burn in Earth’s
upper atmosphere, producing bright
streaks of light called a meteor shower.
Most meteors are caused by dust particles
from comets.
CH
Study Guide
Key Concepts
Section 28.4 Other Solar
System Objects
Rocks, dust, and ice compose the
remaining 2 percent of the solar system.
 Dwarf planets, asteroids, and comets formed
from the debris of the solar system formation.
 Meteoroids are planetesimals that enter
Earth’s atmosphere.
CH
Study Guide
Key Concepts
Section 28.4 Other Solar
System Objects
 Mostly rock and ice, the Kuiper belt objects
are currently being detected and analyzed.
 Periodic comets are in regular, permanent
orbit around the Sun, while others might
pass this way only once.
 The outermost regions of the solar system
house the comets in the Oort cloud.
CH
Our Solar System
28.1 Section Questions
Which scientist first observed the moons of
Jupiter with a telescope?
a. Nicolaus Copernicus
b. Tycho Brahe
c. Isaac Newton
d. Galileo Galilei
CH
Our Solar System
28.1 Section Questions
Which observation provided evidence for the
heliocentric model of the solar system?
a. the nightly motion of the stars
b. the rising and setting of the Sun
c. the retrograde motion of planets
d. the occurrence of meteor showers
CH
Our Solar System
28.1 Section Questions
Kepler determined the relationship between a
planet’s orbital period (P) and the length of its
semimajor axis (a). Which equation correctly
represents this relationship?
a. P3 = a2
b. P2 = a3
c. P = a2
d. P2 = a
CH
Our Solar System
28.2 Section Questions
Earth is the only planet known to have life.
a. true
b. false
CH
Our Solar System
28.2 Section Questions
Which inner planet has the highest average
surface temperature?
a. Mercury
b. Venus
c. Earth
d. Mars
CH
Our Solar System
28.2 Section Questions
Which hypothesis has been suggested to
explain the scarps on Mercury?
a. Mercury’s crust shrank and cracked.
b. Mercury once had plate tectonics.
c. Mercury was eroded by flowing water.
d. Mercury’s surface was covered by lava.
CH
Our Solar System
28.3 Section Questions
Which gas gives Uranus and Neptune their
blue color?
a. hydrogen
b. helium
c. methane
d. nitrogen
CH
Our Solar System
28.3 Section Questions
How many of the four gas giant planets
have rings?
a. one
b. two
c. three
d. four
CH
Our Solar System
28.3 Section Questions
Which elements have the highest abundance
in gas giant planets?
a. iron and nickel
b. hydrogen and helium
c. silicon and oxygen
d. calcium and magnesium
CH
Our Solar System
28.4 Section Questions
Which solar system object is most abundant
in the Oort cloud?
a. rocky planets
b. asteroids
c. comets
d. dwarf planets
CH
Our Solar System
28.4 Section Questions
What causes most meteor showers?
a. dust from the paths of comets
b. asteroids breaking up in the atmosphere
c. pieces from the Moon or Mars
d. particles left from the interstellar cloud
CH
Our Solar System
28.4 Section Questions
Which characteristic must a dwarf planet have?
a. It must be smaller than Pluto.
b. It must be beyond Neptune.
c. It must be rocky.
d. It must be spherical.
CH
Our Solar System
Chapter Assessment
Questions
Which inner planet has retrograde rotation?
a. Mercury
b. Venus
c. Earth
d. Mars
CH
Our Solar System
Chapter Assessment
Questions
Suppose that two objects in space move apart
until the distance between them is double. How
does the gravitational force between these
objects change?
a. It decreases by a factor of two.
b. It decreases by a factor of four.
c. It decreases by a factor of eight.
d. It decreases by a factor of ten.
CH
Our Solar System
Chapter Assessment
Questions
Which statement describes the gas giant planets?
a. They have a high density.
b. They have a thin atmosphere.
c. They have a cratered surface.
d. They have many moons.
CH
Our Solar System
Chapter Assessment
Questions
Which planet has an axis of rotation that is
nearly in its orbital plane?
a. Jupiter
b. Saturn
c. Uranus
d. Neptune
CH
Our Solar System
Chapter Assessment
Questions
How do comet tails form?
CH
Our Solar System
Chapter Assessment
Questions
Possible answer: As a comet approaches
the Sun, ices in the comet vaporize, or turn to
gas. Dust is also released as the comet
dissipates. Particles and radiation streaming
away from the Sun then push the gas and
dust away from the Sun. The gas often forms
a blue tail that points directly away from the
Sun. The dust sometimes forms a separate
white tail because it is not pushed as much by
the solar particles and radiation.
CH
Our Solar System
Standardized Test
Practice
Who described the behavior of gravity?
a. Tycho Brahe
b. Clyde Tombaugh
c. Nicolaus Copernicus
d. Isaac Newton
CH
Our Solar System
Standardized Test
Practice
Which characteristic distinguishes Earth from the
other inner planets?
a. the presence of an atmosphere
b. the presence of an iron core
c. the presence of volcanoes
d. the presence of surface oceans
CH
Our Solar System
Standardized Test
Practice
Examine the illustration. What relationship
exists between the areas of the segments of
the planet’s orbit?
CH
Our Solar System
Standardized Test
Practice
Answer: Kepler’s second law states that
a planet sweeps out equal amounts of
area in equal amounts of time. Therefore,
each segment of the planet’s orbital
ellipse has the same area.
CH
Our Solar System
Standardized Test
Practice
Where are most of the asteroids in the
solar system?
a. between the orbits of Mercury and Venus
b. between the orbits of Earth and Mars
c. between the orbits of Mars and Jupiter
d. between the orbits of Uranus and Neptune
CH
Our Solar System
Standardized Test
Practice
How is Pluto classified by astronomers?
a. as an outer planet
b. as a dwarf planet
c. as a large comet
d. as a small solar system body