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Wright, David. "Travel Guide to the Solar
System." Chain Reaction 3 (2001): 12-15.
Excerpt from Chain Reaction Volume 3, Number 1,
Fall 2001
Pages 12-15
http://chainreaction.asu.edu
Chain Reaction Magazine
is produced by the Office of Research Publications and
published by the Vice Provost for Research at Arizona
State University. The publication of Chain Reactionis
not financed bystate appropriated funds.Persons or
publications wishing to reprint articles, illustrations, or
photographs carried in Chain Reactionshould contact the
editor.Clippings of published excerpts are appreciated.
Correspondence regarding editorial contentshould be sent
to the Editor at:
Chain Reaction Magazine
ASU Research Publications
P.O. Box 878206
Tempe, AZ 85287–8206
Tel: 480.965.1266
Fax: 480.965.9684
E-mail address: [email protected]
Editor: Conrad J. Storad
Art Director: Michael Hagelberg
Senior Writer: Diane Boudreau
Contributing Writers: Jack Farmer, Charles Kazilek,
Matthew Shindell, Lynette Summerill, David Wright
Contributing Photographers: Brad Archer, Jack Farmer,
Sheri Klug, Laurie Leshin, Kim McDonald, Michael Milstein,
NASA, John C. Phillips
WHAT ARE PLANETS MADE OF?
the rocky planets
Of the nine planets in our solar system, the four inner planets–
Mercury, Venus, Earth, and Mars–are relatively small, dense, and rocky.
The rocky layers are mainly silica. The centers of these planets are metal,
mostly iron and nickel. The outer planets include Jupiter, Saturn, Uranus,
and Neptune. Each is primarily a large ball of dense gas, mainly hydrogen,
with some methane, ammonia and helium. Pluto is the outermost
of the nine planets. It is a very small, rocky ball of ice and frozen methane.
M e rc u ry
Ve n u s
E a rt h
Mars
and
P lu t o
[
T R AV E L G U I D E
TO THE
Solar
System
C A T A L Y S T S
make things happen.
They speed up reactions
and make some ingredients combine
that could not without them.
by
David Wright
Earth is just one of nine planets
This
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that orbit Sol, the star we call the sun.
Scientists have learned a lot about our solar neighborhood during
the past few decades. Planetary geologists study the extreme conditions on Earth and other planets in an effort to understand what those
bodies are like and how they formed. Astrobiologists study life under
Earth’s most hostile conditions in an effort to predict where life might
exist on other planets. To date, the only place life has been found is on
the surface of the Earth. And the surface is just one part of our planet–a thin
zone between the atmosphere and crust. Earth can be divided into layers
like an onion: atmosphere, crust, mantle, outer core and inner core.
Conditions everywhere but the surface appear intolerable to life. Ten miles
above Earth’s surface, the temperature is 110 degrees below zero. The pressure
is only one-tenth of that found at the surface. The upper atmosphere is
bombarded with high-energy solar radiation. The gases there are chemically
reactive. Earth’s crust is made of pieces called tectonic plates. Earthquakes can
e
r
occur as a result of the incredibly slow but powerful motion of tectonic plates
sphe
atmost
u
Cr
ates
sliding next to each other. Volcanoes are found in the areas where these
silic
Solid
tle–
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plates crunch together. Below the crust lies the mantle. It is made of
s
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rocky materials, mostly silica. Below the mantle lie the outer and
ica
id sil
–Sol
core
r
e
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inner cores, made of molten iron and nickel. Gravity squeezes
Ou
on
ir
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ickl
all of Earth’s layers toward the center. The temperature
re–N
r co
Inne
at the inner core is 13,000 degrees Fahrenheit.
That’s as hot as the surface of the sun. The pressure at Earth’s
center is 4 million atmospheres. That’s 50 times greater than
the pressure needed to make diamonds! Compared to Earth as
a whole, the surface has only a very narrow range of conditions.
C h a i n R e a c t i o n . 3
12
the gas planets
Ju p i t e r
Sat u r n
Uranus
Ne p t u n e
New Star
Watching the Earth
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Scientists use satellite images
to study comets, asteroids, and
other planets. At ASU, researchers
use the same technology to study
cities and deserts right here on Earth.
The Advanced Spaceborne Thermal
Emission Radiometer (ASTER) peers
down at the Earth from a NASA
satellite launched in early 2000.
The device is part of the Mission to
Planet Earth project. ASTER produces
both color and infrared images of
the Earth. Scientists use different
techniques to analyze the images,
which can reveal a wealth of information. Phoenix is among 100 cities
being studied as part of this project.
The project also focuses on deserts
around the world, including Arizona's
Sonoran Desert. Scientists will watch
these areas for changes in size and
vegetation, among other things.
All the outer gas-giant
planets have rings like
Saturn’s. However, they
are so thin and faint that
they were unknown until
recently. Scientists were
able to detect the rings
with powerful new telescopes, and by visiting
spacecraft.
THEMIS used both infrared and visible light to make this image.
Infrared light reveals the temperature of the Earth. Most of the view is of the night
side of Earth. The instrument measured temperatures of minus 58 degress Fahrenheit
in Antarctica and about 48 degress Fahrenheit in Australia. The readings were
within a few degrees of temperatures measured by humans on the Earth.
13
h t t p : / / c h a i n re a c t i o n . a s u . e d u
Ea rt h i s a v e ry s p e c i a l p l ac e .
PLANET
Of course, we humans have a biased opinion about this planet,
because the temperature, pressure, and chemical composition
on Earth are ideal for supporting a wide variety of life forms.
However, conditions on planetary neighbors in our solar system
are quite different. Compared to these other places, the surface
of Earth seems rather mild, but that’s what makes it home.
T
H I N G S
T O
D O
W H E N
Y O U
d
diameter
Earth=1 (7,926miles)
gravity
Earth=100%
istance
Earth=1
IF YOU WEIGH 100LB ON EARTH,
WHAT YOU WEIGH ON EACH PLANET?
MERCURY
.39
. 38
38%
AU
DISTANCES WITHIN
THE SOLAR SYSTEM ARE OFTEN
MEASURED IN ASTRONOMICAL UNITS—
1 AU IS EQUAL TO THE AVERAGE
DISTANCE BETWEEN THE EARTH
AND THE SUN
V I S I T
Mercury: Fry in solar radiation–you need sunscreen of 250 SPF
Venus: Get cooked, crushed and dissolved in acid
Mars: Puff up and freeze
Jupiter: Weigh as much as you and your best friend together
T R AV E L G U I D E T O T H E
Solar
System
[
T HE
SUN is made mostly from the
two lightest elements in the universe,
hydrogen and helium. Despite the
ultra-light building materials, the sun
has almost 100 times more mass than
all the rest of the planets in the solar
system combined. The sun's crushing
gravity squeezes and heats gases
to temperatures of 15 million degrees–
hot enough to trigger nuclear fusion
reactions. These reactions power the
sun and result in the light we see and
the heat we feel here on Earth. Above,
the image shows huge loops of ionized
gas that follow magnetism that swirls
out from our sun. The loops are many
times bigger than the entire Earth.
C h a i n R e a c t i o n . 3
Mercury is the planet closest to the sun.
It receives tremendous amounts of solar
radiation. There is almost no atmosphere
to help distribute this energy evenly. The
temperature on the sunlit side of Mercury
is 800 degrees Fahrenheit, hot enough to
melt lead into a gooey soup. But a different
world exists on the dark side. Temperatures
there can plunge to a frigid 280 degrees
below zero. No other planet is so different
from one side to the other. Mercury also
lacks an atmosphere to protect the surface
from meteorite impacts. As a result, Mercury
is heavily cratered, just like Earth’s moon.
Venus is Earth’s closest planetary neighbor.
The second planet does not receive as much
solar radiation as Mercury. However, Venus
has an atmosphere heavy in carbon dioxide,
a powerful greenhouse gas. The thick atmosphere traps heat from the sun causing the
temperature on Venus to soar above 900
14
degrees Fahrenheit. That’s hotter than
the sunny side of Mercury! On Venus, thick
clouds of sulfuric acid are blown around by
hurricane winds of up to 220 miles per hour.
The air pressure there is about 90 times sea
level on Earth, which would not make for
a pleasant visit. You would be cooked,
crushed, and dissolved in minutes.
Here on Earth, a wide range of conditions
produce many different environments for
living things. The Earth’s poles are frigid.
The equator is sweltering. The atmosphere
at the highest mountaintops is too thin for
humans to breathe. At the bottom of deep
ocean trenches, the pressure of seawater
is so great it can crush a submarine. Near
a volcano, acidic gases burn skin, lungs,
and eyes. Near the Dead Sea and Great
Salt Lake, soil is severely alkaline. Yet most
of Earth’s surface supports life that is well
suited to its environment.
VENUS
EARTH
MARS
JUPTIER
SATURN
URANUS
NEPTUNE
PLUTO
.94
1.0
.53
11.2
9.4
4.0
3.9
.18
91%
10 0 %
38%
23 0 %
93%
8%
115%
5%
AU
AU
AU
.72 1.0 1.5 5.2 9.5 19.2 30 39.4
AU
↑
AU
AU
AU
AU
Our sun is a relatively small, medium temperature star. Astronomers call it a yellow dwarf.
Giant, hot stars such as Rigel–found in the constellation Orion–give off much more light
at wavelengths of blue and ultraviolet. Cooler, red-giant stars such as Betelgeuse
(pronnounced “beetle juice”)–also found in Orion–have a huge wispy outer atmosphere.
Betelgeuse would fill our Solar System from the sun to the orbit of Mars.
Asteroids found here
Earth’s orbit
Neptune’s orbit
Pluto’s orbit
Mars is known as the Red Planet because
it is covered with red iron oxide dust.
The atmosphere contains mostly carbon
dioxide, some nitrogen, and a little water
vapor. The atmospheric pressure on Mars
is only 1/100th Earth’s, yet there are strong
winds that kick up the red dust into storms
than can cover the entire planet and last for
a year or more. Standing on Mars, the sky
would appear pink from tiny particles of iron
oxide in the atmosphere. There is water on
Mars, but the average temperature is a frigid
40 degrees below zero. Most of that water
is frozen as tiny ice crystals found in clouds
or as part of the large ice caps that cover
the planet’s poles. During the Martian winter,
it gets so cold that carbon dioxide from the
atmosphere condenses, covering the polar
ice caps with a frosting of dry ice.
One of the best-known features on Jupiter
is the Great Red Spot, first observed by
astronomers on Earth more than 300 years
ago. The spot is actually a giant storm large
enough to swallow two Earths. Wind speeds
within the storm can reach hundreds of miles
per hour. Below Jupiter’s atmosphere lies
an outer mantle, which is made of liquid
molecular hydrogen and helium. Below that,
the inner mantle is made of liquid metallic
hydrogen, a form of hydrogen unknown on
Earth. Jupiter’s rocky core is much larger
than Earth. It also is extremely hot–more
than 54,000 degrees Fahrenheit! Jupiter also
has an unsolved mystery. Because it is so
far from the sun, the giant planet receives
very little solar radiation. Yet Jupiter radiates
more energy than it receives from the sun.
No one knows why.
Jupiter is the largest gas giant. A fish bowl
the size of Jupiter could hold 1,300 Earths,
yet Jupiter is only 318 times heavier than
Earth. Why? Because Earth is four times
denser than Jupiter. The atmosphere of
Jupiter contains mostly hydrogen, some
helium, and trace amounts of water,
ammonia, and other gases. Its upper atmosphere is about 180 degrees below zero.
Saturn, Uranus, and Neptune are gas
giants similar to Jupiter. They are made of
hydrogen and helium, mostly in liquid form.
Each of these planets is very cold on the
surface and extremely hot at the core.
They also are very far away from the sun.
Daylight on Saturn is only like twilight
on Earth, and even dimmer on Neptune.
Pluto is the smallest planet.
Astronomers at the Lowell Observatory
in Flagstaff, Ariz., discovered Pluto
in 1930. It is the only planet known to
have solid methane ice. Some scientists
believe Pluto is about the same today
as it was when the solar system was
formed 4.6 billion years ago.
In addition to the nine planets, there
are 61 moons within our solar system.
Some of these moons have dramatically
different conditions. Triton is a moon
of Neptune. At 391 degrees below zero,
Triton is the coldest object in the solar
system. Jupiter’s moon Io has many
active volcanoes that shoot plumes
of lava hundreds of miles above the
surface. On Miranda, a moon of Uranus,
cliffs stretch more than 12 miles high.
Asteroids, comets, and meteors fill
out the picture. A few asteroids such
as Vesta are large enough to qualify
as tiny planets, though none have
atmospheres. All these small bodies
are thought to be remnants of the
original formation of the solar system,
mere crumbs left after the monster
gas giants gobbled most of the gas
and dust available to form planets.
David Wright is a research professional
at ASU’s Center for Solid State Science.
He is also a mentor for the “Science is Fun”
internship in the ASU Service Learning Program.
For more information, see the article on page 32.
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