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Moons
The satellites of the solar system
Moons of our solar system
• As of July 2009, there are 336 known natural
moons in our solar system. 168 moons orbit
the "full-size" planets (Earth, Mars, Jupiter,
Saturn, Uranus, and Neptune), while 6 moons
orbit the smaller "dwarf planets" (Ceres, Pluto,
Haumea, Makemake, and Eris). Others orbit
asteroids and Trans-Neptunian objects.
• Mercury and Venus have no moons
Which planet? How many?
•
•
•
•
•
•
•
•
•
Earth – 1 moon – Luna
Mars – 2 moons
Jupiter – 63 moons
Saturn – 62 moons
Uranus – 27 moons
Neptune – 13 moons
Pluto – 3 moons
Haumea – 2 moons
Eris – 1 moon
• When we consider
that Saturn could
have as many as 1
million moons, the
question arises,
“What constitutes
a moon?”
What is a moon?
• A moon is a natural satellite of a celestial
body. It can orbit a planet, an asteroid,
etc.
• Usually a moon orbits either a planet or a
dwarf planet
• The official size of a moon is still being
debated and it does not appear that it will
be settled soon.
Ten largest moons in the solar system
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Ganymede - Jupiter - 5268 kilometers in diameter
Titan - Saturn - 5150 kilometers in diameter
Callisto - Jupiter - 4806 kilometers in diameter
Io - Jupiter - 3636 kilometers in diameter
Moon - Earth - 3474 kilometers in diameter
Europa - Jupiter - 3122 kilometers in diameter
Triton - Neptune - 2706 kilometers in diameter
Titania - Uranus - 1578 kilometers in diameter
Rhea - Saturn - 1528 kilometers in diameter
Oberon - Uranus - 1523 kilometers in diameter
Oddball moons
• Triton travels around Neptune backwards and could
be a captured body from the Kuiper Belt. In fact,
Triton may look a lot like Pluto.
• Titan, the second largest moon in the solar system, is
an icebox Earth, with a thick atmosphere, methane
meteorology, and youthful surface.
• Ganymede’s icy mantle could contain a liquid ocean
layer, but evidence for that is not conclusive.
Which is the largest moon in the solar
system?
a.
b.
c.
d.
Luna
Ganymede
Titan
Triton
The planet with the most moons is
a.
b.
c.
d.
Saturn
Jupiter
Neptune
Venus
A moon is….
a. Anything that orbits a celestial body that’s
bigger than a breadbox
b. a natural satellite of a celestial body
c. Bigger than a truck
d. A natural satellite of a celestial body that
orbits a planet in the same direction as the
planet’s rotation
The moon that orbits it’s planet in the
direction opposite the planet’s rotation is
a.
b.
c.
d.
Ganymede
Io
Triton
Titan
How do we know what we know about
the moons?
•
•
•
•
•
•
•
Mariner 1-10 – 1962 to 1973
Pioneer 10 and 11 – 1972 and 1973
Voyager 1 & 2 – 1977
Galileo – 1989
Cassini - 1997
LRO (Lunar Reconnaissance Orbiter) - 2009
Hubble (1990) and Kepler (2009)
Luna – the Earth’s
moon
Luna
• The Earth’s only natural satellite
• Second brightest object in our sky
• Albedo of Luna is .07 (reflects 7% of the light
that hits it), surface is color of charcoal
• Fifth largest satellite in the solar system
• 1/4th the diameter of the Earth
• 1/81st of the Earth’s mass
• Synchronous rotation with the Earth – we
always see the same side of the moon
The two sides of the moon
The side we always see
The “dark side of the moon”
Actually we see more than we know…
• Due to the lunar
libration, or a slow
rocking back and forth
motion, we actually see
about 59% of Luna’s
surface on the side that
faces us.
The side hardly anyone sees…
• Taken by Clementine
spacecraft, this is a
mosaic picture of the
south pole of Luna
What we see changes…
• What we see depends on the phase of the moon
from the sliver of a new moon to a full moon when
the moon is behind us, reflecting the Sun’s light
What we see also depends on how
close Luna is to the Earth…
What is the cause of the rocking
back and forth motion?
• May be due to
extended influence of
Earth’s gravity on the
moon while it is
retreating from the
Earth
• Moon’s core is actually
off-center
What are the numbers?
• Moon Numbers
Size: 3,476.2 kilometers -- 0.2725 Earths -14th largest solar system body
Orbit: 384,400 kilometers from Earth
Calendar: 1 lunar day = 29.53 Earth days
• Our Moon is retreating (moving away) at
about 3.8 centimeters (1.5 inches) per year.
Our moon orbits the Earth
a.
b.
c.
d.
24,000 km away.
384,000 km away.
Whenever it feels like it.
Every couple of months or so.
Luna is the ________ largest satellite
in the solar system.
a.
b.
c.
d.
Second
Third
Fourth
Fifth
Internal structure of our Moon
• Geologically distinct
mantle, crust and core
• Solid inner core is
probably high in iron
content approximately
240 km in diameter
• Liquid iron outer core
and an area of partially
melted boundary
between core and
mantle
Crust
• The dark, featureless areas are called maria,
thought by early observers to be seas on the
surface
• Mare are solidified pools of basaltic lava
• Maria are found almost exclusively on the side
facing the Earth and make up 31% of the
surface
• Lighter colored regions, terrae, are highlands
• It is not made of cheese…sorry
• Neither is there a man in the moon
Where did it come from?
Three traditional theories
1.Moon and Earth developed at the same time
(condensation hypothesis)
2.Moon was made of material that came from
the Earth (fission hypothesis)
3.Moon was captured by the Earth’s gravity
(capture hypothesis)
Large-impact hypothesis
• Large celestial body struck the Earth in it’s
early stages
• Most of the iron merged with Earth and
differentiated into the core
• Most iron poor debris formed a ring around
Earth that accreted into Luna
• Evidence? Composition of lunar rocks, signs
of intense heat,