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The Planets
SPACE
Learning Goals

To be able to describe
the planets of our solar
system
Classifying a Planet

To be considered a planet, a celestial object must:
1.
Orbit a star (such as the Sun) and no other celestial object
2.
Contain enough mass so that its gravity pulls it into a round
or spherical shape
3.
Be able to clear other celestial objects out of its orbit
Planetary Motion - Revolution

All of the planets revolve, or travel around the Sun

The orbits are elliptical, or oval-shaped

Earth completes one revolution around the Sun in about 365
days, which we call 1 year

The other planets take different amounts of time to complete
one revolution (Mercury – 88 days; Neptune – 164 years)

Discovered in 1930
Planetary Motion - Rotation

Planets also rotate, or spin or turn on an axis

An axis is an imaginary line around which an object rotates

Earth’s axis runs from pole to pole

Most planets rotate in a west-to-east direction, similar to Earth

Venus rotates in the opposite direction
Planetary Motion - Rotation

Earth’s rotation causes our day and night

Earth completes one rotation every 24 hours, which is one day

The amount of time a planet takes to rotate is equal to the
length of one day on that planet
Mercury
Mercury

Closest to the Sun

Hot days (430 °C); Cold nights (-170 °C)

Mercury is 0.38 AU from the Sun

Revolution of 88 days (= 1 year)

Rotates once every 59 days (= 1 day)

No moons

Temperatures range from -170 °C at night to 430 °C during the day

Mariner 10 first visited in 1974 & 1975, Messenger began orbiting in 2011
Venus
Venus

Volcanoes (toxic atmosphere)

Brightest in night sky after Moon

Hottest planet (450 °C, max 480 °C)

Venus is 0.72 AU from the Sun

Revolution of 224.7 days

Rotation of 243 days

Diameter is 0.95 times Earth’s

No moons

Opposite rotation to Earth
Earth
Earth

Liquid water

Sustains life

Earth is 1 AU from the Sun

Revolution of 365 days

Rotation of 24 hours

Diameter is 12, 740 km

1 moon (the Moon)

Temperatures range from -85 °C to 65 °C
Mars
Mars
Red soil (red planet)
 Most studied planet
 Evidence of water, volcanoes, glaciers in the past
 Mars is 1.52 AU from the Sun
 Revolution – 687 days (1.88 years); Rotation 24.6 hours
 Diameter is 0.53 times Earth’s




2 moons (Phobos and Deimos)
Temperatures range from -133 °C to 27 °C
Mariner 4 flyby in 1965, 2 Viking landers in 1976, Mars Pathfinder in 1997,
Mars Surveyor (2000’s), Mars Science Laboratory (2012)
Terrestrial Planets Relative Sizes
Jupiter
Jupiter

Largest planet

Great Red Spot – giant hurricane

63 known moons (Io, Europa, Ganymede, Callisto)

Jupiter is 5.20 AU from the Sun

Revolution of 11.9 years

Rotation of 9.9 hours

Diameter is 11.0 times Earth’s

Temperature around -153 °C
Jupiter

Visited by Pioneer 10 in 1973, then Pioneer 11, Voyager
1 and 2, Ulysses, Cassini-Huygens, and Galileo orbited it
for 8 years

1994, comet Shoemaker-Levy 9 was torn apart and
pieces crashed into Jupiter
Saturn
Saturn

Over 1000 rings

62 known moons (Titan)

Saturn is 9.5 AU from the Sun

Revolution of 29.46 years

Rotation of 10.2 hours

Diameter is 9.4 times Earth’s

Temperature around -185 °C

Visited by Pioneer 11 (1979), Voyager 1 and 2, Cassini (recent)
Uranus
Uranus

Rotates on its side

27 moons and some rings
(1977)

Strong winds

Uranus is 19.2 AU from the
Sun

Temperature around -210 °C

Visited by Voyager 2 in 1986

Revolution of 83.75 years


Rotation of 17.2 hours
Discovered as a planet in
1781

Diameter is 4 times Earth’s
Neptune
Neptune
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Predicted and then discovered in 1846

Neptune is 30 AU from the Sun
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Revolution of 164.8 years
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Rotation of 16.1 hours

Diameter is 3.9 times Earth’s
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13 Moons and some rings

Temperature around -220 °C

Visited by Voyager 2 in 1989
Relative Size of Jovian Planets
Distances from Sun
Tilt of Planets
Dwarf Planets

A dwarf planet is a celestial object that orbits the Sun and
has a spherical shape, but does not clear its orbit

Five recognized dwarf planets: Ceres, Pluto, Haumea,
Makemake, Eris

Scientists estimate another 70 000 icy objects beyond
Neptune

Pluto takes 248 years to orbit Sun, Eris takes twice as long
Asteroid Belt

An asteroid belt is located between the
orbits of Mars and Jupiter

The dwarf planet Ceres is located in the
asteroid belt
The Moon
The Moon

Earth’s only natural satellite

About 384,000 km from Earth

The moon revolves around Earth and rotates on
its axis every 27.32 days

For this reason, we always see the same side of
the moon

Diameter is 0.27 times Earth’s

Gravity is 1/6 of Earth’s

The Moon is responsible for tides on Earth
Success Criteria

I CAN describe the similarities and differences
among the planets in our solar system