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Pearson Prentice Hall
Physical Science: Concepts in Action
Chapter 25
The Solar System
25.1 Exploring the Solar System
• Objectives:
• 1. Compare and contrast the geocentric and
heliocentric models of the solar system
• 2. Describe the orbits of the planets around
the sun and explain how gravity and inertia
keep the planets in orbit
• 3. Name the components of the solar
system
• 4. Identify different technologies used for
exploring the solar system
Geocentric vs. Heliocentric
• The geocentric model is from ancient
Greece
• In the geocentric model, Earth is stationary
while objects in the sky move around it
• In the heliocentric model, Earth and the
other planets revolve around the sun
• Imagine the path of Earth’s orbit traced on
a table
• Def: the ecliptic plane is the path of Earth’s
orbit
Gravity plus Inertia & Components of
the Solar System
• Gravity and inertia combine with each
other to keep the planets in orbit
• Without gravity, planetary inertia
would cause them to fly off in space
• The components of the solar system
are the sun, the planets, their moons,
and a variety of smaller objects that
mostly revolve in the same plane
around the sun
Exploring the Solar System
• Modern technology including telescopes, piloted
spacecraft, & space probes has allowed
scientists to explore the solar system
• Def: a space probe in an unpiloted vehicle that
carries scientific instruments into space and
transmits information back to Earth
• NASA launched 2 vehicles, Spirit & Opportunity
to land on Mars in 2004 for a 3 month mission
• They are still sending information back to Earth
today
• The scientist who monitors them is at UNR
25.2 The Earth-Moon System
• Objectives:
• 1. Explain why the moon lacks atmosphere
& the effect this has on the range of
temperature on the moon
• 2. Describe the features of moon’s surface
• 3. State a theory about the formation of the
moon
• 4. Explain the phases of the moon, tides &
eclipses & interpret diagrams of these
events
No Atmosphere/Surface Features
• Moon’s gravity is too weak to hold onto
gas molecules
• The lack of atmosphere allows moon’s
surface temperature to vary
tremendously
• The major surface features are maria,
highlands and craters
• Def: maria are low, flat plains formed by
ancient lunar lava flows
Features plus Formation
• Def: highlands are rough mountainous regions
that cover most of moon’s surface
• Lunar highlands are light-colored areas that
surround the maria
• Def: craters are round depressions caused by the
impact of high speed meteoroids
• Def: meteoroids are chunks of rock that move
through the solar system
• Scientists hypothesize that the moon was formed
after an enormous collision in Earth’s history
• The collision was probably caused by rocky debris
which was plentiful & hit many planets about 4.6
billion years ago when Earth formed
Phases of the Moon & Eclipses
• Def: the different shapes of the moon visible
from Earth are called phases
• The moon’s phases are caused by changes in
the relative positions of the moon, sun & Earth
as the moon revolves around the Earth
• Def: an eclipse occurs when the shadow of one
body in space falls on another
• Def: a solar eclipse occurs when the moon casts
a shadow on a portion of Earth’s surface
• Def: a lunar eclipse occurs when Earth casts a
shadow on the moon
8 Phases of the moon
New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not
visible (except during a solar eclipse).
Waxing Crescent - The Moon appears to be partly but less than one-half
illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated
is increasing.
First Quarter - One-half of the Moon appears to be illuminated by direct
sunlight. The fraction of the Moon's disk that is illuminated is increasing.
Waxing Gibbous - The Moon appears to be more than one-half but not fully
illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated
is increasing.
Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to
be completely illuminated by direct sunlight.
Waning Gibbous - The Moon appears to be more than one-half but not fully
illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated
is decreasing.
Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight.
The fraction of the Moon's disk that is illuminated is decreasing .
Waning Crescent - The Moon appears to be partly but less than one-half
illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated
is decreasing.
Lunar Eclipse
Tides
• Def: tides are the regular rise and fall of ocean
waters
• Tide are caused mainly by differences in the
moon’s gravitational pull on Earth
• The sun’s gravity affects tides about half as much
as the moon
• Def: spring tide is the combined forces of the
gravity of the sun and the moon
• Def: neap tide is the least tide possible & is due
to first or third quarter moon being at right
angles to the Earth (compared to sun’s position)
• The solar system is the sun and the planets
that orbit around it
• The four planets closest to the sun are the
terrestrial planets
• Def: terrestrial planets are planets similar in
structure to Earth
• The four inner planets are all small, dense
and rocky
• All have a crust, mantle and iron core
• Five planets have been known for centuries:
Mercury, Venus, Mars, Jupiter & Saturn
25.3 The Inner Solar System
• Objectives:
• 1. Compare the terrestrial planets
and describe characteristics of
each
• 2. Define asteroids and state
alternative hypotheses about how
they were formed
Compare and Describe
• Mercury is the smallest and closest to the sun
• Venus is called the evening star or morning
star
• Venus’s atmosphere has the greenhouse gas
effect due to large amounts of CO2 which
traps heat and raise temperature
• The CO2 also causes it to rain sulfuric acid
when it combines with the sulfur in the
atmosphere
• Earth’s atmosphere is suitable for water to
exist as a liquid
• Mars is a major source of study right now,
including experimentation with rovers from
NASA named Spirit and Opportunity
• They landed on Mars in 2004
• The rovers were designed to send information
for 3 months, but functioned for years yielding
information about Martian water and soil
• Spirit was mobile on the Red Planet for over
five years and then functioned as a stationary
science platform for another year before
getting killed off by a Martian winter it
couldn’t avoid”
• As of January 2012, Opportunity still works &
will spend the Martian winter in a sunny
spot until the engineers wake it up in Martian
spring
• In August 2012, NASA landed a much larger,
very expensive rover called Curiosity
• Its mission is to see if Mars ever had the right
conditions to support life
• Mars shows evidence of having had a lot of
water in its past
• other missions to Mars, including manned
missions are being considered
• Mars is sometimes called the “red planet”
Asteroids
• Def: asteroids are small rocky bodies
orbiting the sun
• The region in the solar system where
they are found is called the asteroid belt
• The asteroid belt is between Mars and
Jupiter
• Scientists hypothesize that asteroids are
remnants of the early solar system that
never came together to form a planet
The Inner Solar System
25.4 The Outer Solar System
• Objectives:
• 1. Compare the gas giants and describe
characteristics of each
• 2. Distinguish between planets and dwarf
planets
• 3. Distinguish between comets and
meteoroids and describe their
characteristics
• 4. Locate and describe the Kuiper belt and
Oort Cloud
Gas Giants
• The four outer planets (Jupiter, Saturn,
Uranus and Neptune) are gas giants
• Def: gas giants are planets composed mainly
of hydrogen and helium
• The four gas giants are thought to have small,
dense cores, and dense atmospheres
composed mostly of hydrogen and helium
• Def: a ring is a disk make many small particles
of rock and ice in orbit around a planet
• All of the gas giants have rings
• Jupiter is the largest and most massive
planet in our solar system
• Jupiter has at least 63 moons
• Saturn’s rings are the largest and most
visible from Earth
• Saturn has at least 56 moons, but is
known for its moon named Titan
• Titan is larger than Mercury
• Uranus is believed to have a mantle of
liquid water and dissolved ammonia
• The axis of Uranus’s rotation is tilted
more than 90°
• Neptune’s bluish color comes from the
methane in its atmosphere
• Its largest moon is called Triton and it
has a thin atmosphere and an icy
surface
Dwarf Planets
• Def: a dwarf planet, like a planet, is
spherical and orbits the sun directly, but
a dwarf has not cleared the
neighborhood (more on that in a
moment)
• The definition of planet is that it is a
celestial body in orbit around the sun,
has self-gravity, is not a satellite and
clears the neighborhood around its orbit
• A satellite is any object orbiting a planet,
whether natural or man-made
• Pluto does not “clear the neighborhood” because
it is part of a sea of objects that occupy the same
region of space
• Pluto and its moon Charon have an elliptical orbit
that sometimes crosses into Jupiter’s orbit, thus
lending support to those who want to reclassify it
• Planets must have sufficient force to get other
objects out of their way
• Under the new definition as many a 12 planets
have been proposed
• Officially at this time there are 8 planets in our
solar system
• The astronomers in 2006 came up with the
following proposals & definitions:
• 1. Planets: The eight worlds starting with
Mercury and moving out to Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune
• 2. Dwarf planets: Pluto and any other round
object that "has not cleared the
neighborhood around its orbit, and is not a
satellite."
• 3. Small solar system bodies: All other
objects orbiting the sun
• The Pluto issue will continue to play out for
some time & is not yet settled
Comets, Meteoroids, Kuiper & Oort
• Def: comets are dusty pieces of ice and
rock that partially vaporize when they
pass near the sun
• Def: meteoroids are pieces of rock,
usually less than a few hundred meters in
size, that travel through the solar system
• At the edge of the solar system beyond
Neptune are Kuiper and beyond Kuiper is
Oort
• Most of the objects in the Kuiper belt lie in a
doughnut shaped region close to the ecliptic
plane
• Def: the ecliptic plane is the plane in space
containing Earth’s orbit (the path of Earth’s
orbit)
• Pluto is in the Kuiper belt
• Beyond the Kuiper belt is a great reservoir of
comets called the Oort cloud
• Occasionally objects from the Oort cloud
enter the inner solar system as comets
25.5 The Origin of the Solar System
• Objectives:
• 1. State the nebular theory
• 2. Relate the nebular theory to
the orbits, composition and size
of the planets
The Nebular Theory
• Scientists believe the solar system was
formed by the nebular model
• The nebular theory state that the solar
system formed from a rotating cloud of
dust and gas
• Def: a protoplanetary disk is a large disk
shaped cloud of dust and gas resembling a
giant fried egg rotating in space
• Most of the mass is concentrated in the
center
• The planets eventually formed from the outer
parts of the disk
• The central mass eventually became the sun
• Def: planetesimals were asteroid-like bodies
that eventually combined to form planets
• Def: accretion is the process of adding mass
by colliding with other planetesimals
• The cloud may have been flat as it collapsed,
laying in one plane creating the orbits
• Accretion occurs when small particles collect
and stick together to form large masses
• planetesimals attracted more and more
matter leading to moon sized protoplanets
with their own gravity
• The terrestrial planets ended up close to the
sun and are small and rocky
• This is because the inner solar system was too
hot during formation for ice-forming
compounds to condense
• The gas giants are large and have low densities
because the outer solar system was cool
enough for ice-forming compounds to
condense