6th Grade Science: The Solar System
• Section 1: An Overview of The Solar System
• Section 2: The 9 Planets of The Solar System
What’s in Our Solar System?
• Our Solar System consists of a central star
(the Sun), the nine planets orbiting the sun,
moons, asteroids, comets, meteors,
interplanetary gas, dust, and all the “space”
in between them.
• The nine planets of the Solar System are
named for Greek and Roman Gods and
• The Sun’s age is about 5 billion years.
• Its energy comes from nuclear fusion (where hydrogen is
converted to helium) within its core. This energy is
released from the Sun in the form of heat and light.
Geocentric vs. Heliocentric Theory
• Geocentric Theory (or “Ptolemaic” Theory
– pronounced “Tole-ah-may-ic”) is an
ancient view of the universe based primarily
on religion, philosophy, and mathematical
• Heliocentric Theory (or “Copernican”
Theory) is a revised view of the universe
based on the studies of Nicholas
Copernicus, who was a mathematician in
Geocentric Theory: Basic Beliefs
1. The cosmos (or universe)
1. Is geocentric: has the earth as its center with
the sun and other planets revolving around the
2. Is geostatic: the earth itself does not move
2. Celestial bodies move in uniform, circular
motion around a central point.
3. Celestial bodies are composed of a fifth element:
4. The cosmos is “finite,” which means that it does
not go on forever.
Heliocentric Theory: Basic Beliefs
1. The earth rotates daily on its axis.
2. The earth and the planets revolve around
the sun (a heliocentric model).
3. The earth’s orientation is fixed in space
because of the conical axial motion of the
The 9 Planets of the Solar System
• Planets are categorized according to
composition and size. There are two main
categories of planets:
– small rocky planets (Mercury, Venus,
Earth, Mars, and Pluto)
– gas giants (Jupiter, Saturn, Uranus, and
Life on Mars
What did it possibly look like?
Mr Links’ pictures with the aliens
The Relative Size of the Planets in
the Solar System
Characteristics of Small Rocky Planets
• They are made up mostly of rock and metal.
• They are very heavy.
• They move slowly in space.
• They have no rings and few moons (if any).
• They have a diameter of less than 13,000
• Mercury has a revolution period of 88 days. A
revolution period is the time it takes for a planet to
complete one full orbit around the sun. This is also
called a year.
• Mercury has extreme temperature fluctuations,
ranging from 800°F (daytime) to -270°F
• Even though it is the closest planet to the sun,
recent radar info suggests there is ICE on Mercury!
Scientists believe the ice is protected from the sun’s
heat by crater shadows. It is covered with meteorite
impacts and barely has a trace of an atmosphere.
• Venus is the brightest object in the sky after the
sun and moon because its atmosphere reflects
sunlight so well. People often mistake it for a star.
• The atmosphere of Venus has a large amount of
carbon dioxide gas. Carbon dioxide traps heat in
Venus’s atmosphere, causing the surface
temperatures to increase greatly. We call this
effect the Greenhouse Effect. Venus’s
Greenhouse Effect is so strong that its maximum
surface temperature may reach 900°F.
• Venus has no moons. It has thick yellowish
clouds composed of sulfuric acid driven by fast
winds. Its surface is dry and dusty with craters,
mountains, and volcanoes.
• Earth is the only planet known to support living
• Earth’s surface is composed of 71% water.
– Water is necessary for life on Earth.
– The oceans help maintain Earth’s stable temperatures.
– Water is a primary cause of Earth’s surface weathering.
• Earth has a distinct atmosphere.
– It helps screen harmful radiation from the sun.
– It prevents meteorites from reaching Earth’s surface.
– It traps heat to help maintain Earth’s stable
• Earth has one moon.
• It takes the same amount of time for the moon to rotate once
on its axis as it does for it to orbit the earth (27.3 days).
Thus, the same side of the moon always faces us.
• The moon’s surface is covered in dust and rocky debris
from meteor impacts. It has no water or atmosphere. The
dark areas of the moon are called maria (Maria is a Latin
word meaning “seas”). Maria are large craters which have
been filled by solidified lava.
• The moon reflects light from the sun onto the earth’s
surface. Sometimes the moon may appear reddish-brown in
color as the sunlight is deflected through dust in the earth’s
• The moon’s gravitational effects on the earth are most
apparent in the “coming” and “going” of the tides
• Mars has permanent ice caps at its poles. The ice
caps are composed mostly of frozen carbon
dioxide (what we call “dry ice”).
• Mars has the largest volcano in our solar system:
Olympus Mons. Olympus Mons is approximately
24 km high (15 miles).
• Atmospheric dust makes Mars’s sky pink in color.
• Mars has two moons: Phobos and Deimos
• Pluto is the only planet not visited by spacecraft.
We are not sure of its composition. Based on
current data, scientists believe it is a small, rocky
• Pluto seems to lie on its side: its equator points
straight up, and one of its poles points directly at
• Pluto has only one moon (Charon). Pluto’s moon
is half the size of Pluto itself, which is unusually
large for a moon. Because they are so close in size,
sometimes Pluto and its moon are considered to be
a double planet system.
• Pluto was located and named in 1930.
Characteristics of Gas Giants
• They are made up mostly of gases
(primarily hydrogen & helium).
• They are very light for their size.
• They move quickly in space.
• They have rings and many moons.
• They have a diameter of less than 48,000
• Jupiter is the largest and most massive planet: it’s diameter
is 11 times bigger than that of the Earth’s. Overall, Jupiter
is about 318 times the size of Earth. Jupiter is composed
almost entirely of hydrogen and helium.
• Because Jupiter rotates so quickly, it’s clouds form belts
(low-lying, relatively warm cloud layers) and zones (bright,
high-altitude, cooler cloud layers) that encircle the planet.
• Jupiter’s characteristic Great Red Spot is an enormous
storm, consisting of a spiraling column of clouds big
enough to contain three Earths. The clouds are colder than
the surrounding areas, and so the Great Red Spot sits about
five miles above the upper cloud layer.
• Jupiter has 16 known moons.
• Saturn, like Jupiter, is composed almost entirely of
hydrogen and helium. Saturn is the least dense of
all the planets. In fact, Saturn’s density is less than
that of water.
• Saturn has many rings composed primarily of ice
with some ice-coated rocky particles. Saturn’s
rings are very wide (they extend outward to about
260,000 miles from the surface) but very thin (less
than 1 mile thick).
• Saturn has 18 known moons, some of which orbit
inside the rings!
• Uranus is tilted on its axis at 98°. Because of its
strongly tilted axis of rotation, Uranus essentially
spins on its side as it orbits the sun.
• Uranus is blue in color due to methane gas in its
• Uranus has 11 dark rings surrounding it. These
rings contain some of the darkest matter in our
• Uranus has 15 known moons, and scientists
suspect more lurk within its rings.
• Neptune has the fastest winds on the solar
system: up to 2000 km/hr.
• Neptune is also blue in color due to methane
gas in its atmosphere.
• Neptune has a Great Dark Spot in its
atmosphere. The Great Dark Spot is a huge
storm the size of Earth.