Download The Inner Planets - Germantown School District

THE INNER PLANETS
LESSON 4
OBJECTIVES
• Students will be able to describe the characteristics
that the inner planets have in common.
• Students will be able to identify the main
characteristics that distinguish each of the inner
planets.
WHAT DO THE INNER PLANETS HAVE
IN COMMON?
• The inner planets are small and dense and have
rocky surfaces.
• Often called terrestrial planets which means “Earth”
• All have relatively high densities.
• Rich in rocky and metallic materials, including iron
and silicon.
• Each has a solid surface.
• All have atmospheres except Mercury.
DATA
Planet
Mercury
Venus
Earth
Mars
Diameter
(km)
4,879
12,104
12,756
6,794
Period of
rotation
(Earth days)
58.9
244
1.0
1.01
Average
distance
from sun
0.39
0.72
1.0
1.52
Period of
revolution
(Earth days)
88
224.7
365.2
687
Number of
moons
0
0
1
2
HOW DO THEY DIFFER?
• Size
• Composition
• Distance from the sun
MERCURY
•
•
•
•
Temperature range 430°C to below -170°C
Smallest terrestrial planet
Not much larger than Earth’s moon
Interior made up of dense metal iron
Surface- flat plains and craters; no water and not
much atmosphere
Atmosphere- small in mass= weak gravity, gas
particles easily escape into space, small amounts of
sodium and other gases have been detected around
Mercury
Exploring Mercury- most information comes from
space probes
Mariner 10 flew by Mercury 3 times in 1974 and 1975
Mercury Messenger passed Mercury several times and
began orbiting in 2011
VENUS
• Similar in size and mass to Earth, called “Earth’s
twin”
• Density and internal structure similar to Earth
• Thick atmosphere
• Unusual pattern of rotation
• Hottest surface of any planet
Atmosphere- so thick that it is always cloudy; at
the surface you would be quickly crushed by the
weight of its atmosphere; pressure is 90 times
greater than the pressure of Earth’s atmosphere;
you couldn’t breathe on Venus because its
atmosphere is mostly carbon dioxide
Rotation- takes about 7.5 Earth months to revolve
around the sun and 8 months to rotate once on
its axis; rotates from east to west; maybe because
a large object struck Venus billions of years ago
causing it to change direction or Venus’s thick
atmosphere could have somehow altered its
rotation
Hot Planet- receives more solar energy than Earth
because its closer to the sun; much of the
radiation is reflected by Venus’s atmosphere;
some radiation reaches the surface and is later
given off as heat; carbon dioxide in atmosphere
traps heat so well that it has the hottest surface;
average surface temperature is 460°C
Greenhouse effect- trapping of heat by the
atmosphere
Exploring VenusVenera 7 landed in 1970
Magellan probe landed in 1990
Venus Express
EARTH
• Only planet in the solar system where you could live
easily
• Has liquid water
• Suitable temperature range
• Atmosphere for living things to survive
Water Planet- about 70% of Earth’s surface is covered
with water
Temperature- if Earth were a little closer to
the sun, it would be so hot that liquid water
would evaporate; if it were a little farther
away and colder, water would always be
solid ice
Atmosphere- has enough gravity to hold on
to most gases that make up Earth’s
atmosphere; only planet with an atmosphere
that is rich in oxygen; like Venus, Earth
experiences a greenhouse effect; traps less
heat than Venus’s atmosphere; without the
atmosphere, Earth would be much colder
MARS
• Called the “red planet”
• Reddish color is due to the breakdown of iron-rich
rocks, leaving a rusty dust behind
• Too cold for liquid water
• Does have water ice now and liquid water in the
past
Atmosphere- more than 95% carbon dioxide;
has few clouds but very thin compared to
clouds on Earth; temperatures range from
-140°C to 20°C
Water and Ice- atmosphere is so thin that any
liquid water would quickly turn into a gas; water
is located in the planet’s two polar ice caps
made entirely of frozen water located under the
surface
Volcanoes- some regions have giant volcanoes
that are rarely active anymore; Olympus Mons is
the largest volcano in the solar system
Mars’s Moons- has two very small moons that
are covered with craters
1. Phobos- larger about 22km across
2. Deimos- even smaller 13km across
Exploring Mars- recent missions have focused
on finding signs of water and possible life on
Mars
Spirit and Opportunity- found traces of salts and
minerals that form in the presence of water
Phoenix mission- took samples of soil and found frozen
water near the north polar cap
Mars Express spacecraft- detected methane gas in
Mars’s atmosphere