The Planets

The Solar System

• The solar system is made up of the Sun and all the objects that travel around it

• Planets and their moons, asteroids and comets all revolve around the Sun

• Planets also rotate

Orbital Period

• When an object revolves around a much larger object, it is said to be in orbit

• The time taken for a planet to complete one full revolution around the Sun is its orbital period

• The Earth’s orbital period is 365.25 days

Rotational Period

• Planets also rotate (spin)

• The time taken for a planet to complete one full rotation is its rotational period

• The Earth’s rotational period is 23h 56 min

Comparing Planets

• The rotational period, orbital period, mass and diameter of the other planets are always compared to that of Earth

• Distances are given using the astronomical unit (AU) – equal to the average distance from Earth to the

Sun

The Planets

• Planets are split into three groups:

1.Inner Planets (Terrestrial Planets)

2. Outer Planets (Gas Giants)

Mercury, Venus, Earth and Mars

Jupiter, Saturn, Uranus and Neptune

3. Dwarf Planets

Pluto, Ceres, Eris, Haumea, Makemake

Mercury

• The Roman name for Hermes (the messenger)

Distance from Sun 0.39 AU

Diameter 0.38

Mass 0.06

Rotational Period 59 days

Orbital Period 88 days = 0.24 years

Average Surface

Temperature

350ºC

Surface: Covered with craters

Number of moons 0

Fun Fact: Not visible at night

Venus

• The Roman name for Venus (goddess of love)

Distance from Sun 0.72 Au

Diameter 0.95

Mass 0.88

Rotational Period 243 days

Orbital Period 225 days = 0.62 years

Average Surface

Temperature

470ºC

(hottest)

Surface: Many volcanoes

Number of moons 0

Fun Fact: Rotates east to west

Earth

• Also known as “home”

Distance from Sun 1 Au

Diameter 1

Mass 1

Rotational Period 1 day

Orbital Period 1 year

Average Surface

Temperature

22ºC

Surface: 70% water

Number of moons 1

Fun Fact: Only planet known to sustain life

Mars

• Roman name for Ares (God of War)

Distance from Sun 1.52 Au

Diameter 0.53

Mass 0.11

Rotational Period 25 days

Orbital Period 687 days = 1.88 years

Average Surface

Temperature

-23ºC

Surface: Reddish coloured soil

Number of moons 2 (Phobos & Deimos)

Fun Fact: Atmosphere is mostly carbon dioxide

Jupiter

• Roman name for Zeus (chief of the 12 Olympians)

Distance from Sun 5.27 Au

Diameter 11.25

Mass 318

Rotational Period 10 hours

Orbital Period 12 years

Average Surface

Temperature

–150ºC

Number of moons 63

Fun Fact: Largest planet

Saturn

• Latin name for Cronus (Father of Zeus)

Distance from Sun 9.54 Au

Diameter 9.45

Mass 95

Rotational Period 11 hours

Orbital Period 30 years

Average Surface

Temperature

–180ºC

Number of moons 60

Fun Fact: - Rings are composed of

ice-covered rock & dust

- Less dense than water

Uranus

• Named after the Greek god of the sky (Zeus’s grandfather)

Distance from Sun 19.19 Au

Diameter 4.01

Mass 15

Rotational Period 17 hours

Orbital Period 84 years

Average Surface

Temperature

–210ºC

Number of moons 27

Fun Fact: Rotates on an axis tilted 90° to the solar plane

Neptune

• Roman name for Poseidon (Ruler of the Sea)

Distance from Sun 30.06 AU

Diameter 3.96

Mass 17

Rotational Period 16 hours

Orbital Period 165 years

Average Surface

Temperature

–220ºC

Number of moons 13

Fun Fact: Appears blue because of methane gas

Pluto

• Roman name for Hades (Ruler of the dead)

Distance from Sun 39.5 AU

Diameter 0.19

Mass 0.002

Rotational Period 8 days

Orbital Period 248 years

Average Surface

Temperature

–220ºC

Number of moons 1

Fun Fact: Was classified as a planet until mid-2008

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The Other Dwarfs

• Ceres – Located in the asteroid belt– Largest object in the asteroid belt

• Haumea– Orbits the Sun beyond Neptune– Has two moons

The Other Dwarfs

• Makemake– Orbits the Sun beyond Neptune– The brightest object in the Kuiper Belt, other

than Pluto

• Eris– Orbits the Sun beyond Neptune– The largest of the dwarf planets– Has one moon (Dysnomia)