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 Planet Study Guide



 Rocky world with almost no atmosphere

Sun appears 9 times as large as it does from the Earth because Mercury is the

Closest planet to the sun

Moves more quickly around the sun than any other planet (88 days to complete one revolution)

Named after speedy messenger of the Roman gods

 No rings

 No moons

 Temperature cold at night Hot during the day





Named for the Roman goddess of beauty and love

Same diameter, mass and density as earth so astronomers call it the Earth's twin

Very thick cloud covering (5 times as dense as earth)

Year shorter than day

95% of its atmosphere is C02

Has craters

 no rings

 no moons

 Brightest planet in the sky

 2nd planet from the sun

 Closest planet in size to the earth

 Covered in volcanic rock



Similar size to Venus

70% of its surface is covered by water

78% of is atmosphere is Nitrogen

Only known planet to support life

Has one moon

Has seasons due to the tilt of its axis


MARS (The Rusty Planet)

Known as The Red Planet (rust)

 Surface is rocky and heavily cratered

 Martian soil is coated with a reddish compound called iron oxide (commonly known as Rust!)

In ancient times this color reminded people of blood and they though of Mars as a warrior planet

Named after the Roman god of war

Two tiny moons that circle Mars are called Phobos and Deimos (from the Greek-words for fear and terror)

4th planet from the sun

 Gravity close to 1/3 of Earth's

 2 moons (Phobos and Deimos)

 4 large, inactive volcanoes


 Has a rotation time most similar to Earth's

 People once thought there were canals on the surface, but they were wrong




One hundred Earths could be strung around Jupiter as if they were a string of pearls

 Jupiter is so big and bright in the night sky that the Romans named this planet after their king of gods

 Made primarily of hydrogen and helium gases

At its core, scientists believe temperatures may reach 5 times that of the sun

5th planet from the sun

Shortest rotation time (shortest day – 10 hours)

Largest planet

 Hotter than earth

 Known for "Great Red Spot"

The red spot is a very large storm that has lasted for centuries

SATURN- (A world of many rings)

Famous for its rings

Rings made from rocks and ice

It's rings were discovered by Galileo

It's rings are made mainly of icy particles

Voyager revealed that Saturn has at least seven major rings, lettered from A to G

Saturn spins so fast that it is flattened at the poles and bulges at the equator

Has more moons (satellites) and rings than any other planet

31 satellites discovered so far

6th planet from the sun – the 2nd largest planet

Gas planet

Least dense planet – if there was an ocean large enough to fit Saturn it would float on it

Very little atmosphere – made of helium

It's moon. Titan, is larger than the planet. Mercury 


URANUS - (A planet on its side)

Most distant planet that can be seen with the unaided eye

Known as one of the giant twins (along with Neptune)

Named for the father of Saturn in Roman mythology

With the discovery of Uranus, the solar system doubled because Uranus is almost twice as far from the sun as Saturn

A gas giant covered by a thick atmosphere made of hydrogen, helium and methane

Entire planet is tinged with a greenish-blue color

Covered by an ocean of superheated water that may have been formed from melted comets

The axis of Uranus is tilted at an angle of about 90° so Uranus seems to be tipped completely on its side.

 Has eleven known rings

 7th  planet from the sun

Gas planet

21 known satellites





Named for the Roman god of the sea

Neptune and Uranus are often called the twin giants because they are about the same size, mass and temperature

They both glow with a blue-green color

Surface is probably an ocean of water and liquid methane, covering a rocky core

Has five rings made of dust and rock

Has eight moons

Voyager discovered new moons and rings around Neptune in 1989


 PLUTO (A double planet)

Named for the Roman god of the underworld

Smallest and least massive planet

Farthest known planet from the sun

May be an escaped moon of Neptune

Made mainly of various ices, primarily methane ice

Pluto’s moon’s name is Charon.

Charon is about half the size of Pluto.  Because of the closeness in size, astronomers consider Charon and Pluto to be a double planet.



Only an average –size star

Largest object in the solar system

About 109 times the diameter of the Earth

If the sun were hollow, more than 1 million Earths’ could fit inside

Surface temperature is about 10,000° F

About 4.6 billion years old

Made of extremely hot gases

Four main layers of the sun (corona, chromosphere, photoshere, core)




Often called a "snowball in space"



Also known as a "shooting star"



May be made of rocks, metals or a combination of the two

Known as “flying mountains” or “minor planets”

Most are small and irregularly shaped but a few are huge