Moons of our Solar System

by Mr. McKinsey, November, 2007

A Moon for Every Planet?

• Most planets have moons. Even dwarf planets have moons. Only Mercury and Venus do not have moons.

• Moons vary in size, in composition, and in many other ways.

Gravity

• The sun’s gravity keeps planets, moons, comets

and asteroids in our solar system.

• Each planet’s gravity keeps its moon or moons

in orbit around the planet.

• The pull of gravity depends on the size of the

objects and their distance from each other.

• Close objects pull harder than distant ones.

Moon Characteristics

• Atmosphere

• Moon diameter

• Surface appearance

• Distance from host planet

• Size compared to host planet

• Amount of reflected light (albedo)

Comparing Moons

Moons of our

Solar System are

large and small,

smooth and rough,

near and far.

Moon Atmospheres

Moon Atmosphere?

Earth’s Moon No

Phobos No

Io Yes!

Ganymede No

Triton Yes!

Jupiter’s Galilean moons

Io has an atmosphere.

Moon Diameters

Moon Diameter in Kilometers

Earth’s Moon 3,476.2

Phobos 22.4 (average)

Io 3,643.2

Ganymede 5,262.4

Triton 2,706.8

Earth’s Moon and Neptune’s Triton to the same scale.

• Largest moon in the solar system

Ganymede -8th largest world

Io

12th largest world

Surface Appearance

Moon Surface Appearance

Earth’s Moon Rocky, cratered

Mars’ Phobos Rocky, smooth

Jupiter’s Io Rocky, volcanic

Jupiter’s Ganymede Cratered, icy, grooved

Triton Icy, volcanic

Phobos, moon of Mars

Phobos photographed from Mars

Io has activevolcanoes.

Io’s Volcanoes

• Volcanic eruptions change Io’s surface

Ganymede

Ganymede’s complex surface has grooves, craters, lava flows, mountains, and water ice.

Neptune's Triton from a distance of 530,000 kilometers (330,000 miles).

Distance from Moon to Planet

Moon Distance from Moon to Planet in Kilometers

Moon 384,467

Phobos 6,000

Io 421,600

Ganymede 1,070,400

Triton 354,760

Neptune (top) and its moon, Triton (bottom)

Ratio of Moon Diameter to

Planet Diameter, as % of Planet Diameter

Moon Ratio Expressed as a %

Earth’s Moon 27.37%

Mars’ Phobos 0.33%

Jupiter’s Io 2.60%

Jupiter’s Ganymede 3.76%

Triton 5.52%

Jupiter seen below its moon, Io

Reflected Sunlight (Albedo)Moon Percent of Sunlight

Reflected by Moon Surface (Albedo)

Earth’s Moon 7% (0.07)

Phobos 6% (0.06)

Io 61% (0.61)

Ganymede 42% (0.42)

Triton 7% (0.07)