Download Exploring the Solar System - The Federation of Galaxy Explorers

Federation of Galaxy Explorers
The Solar System
LEARNING OBJECTIVES
Upon completion of this chapter Mission Team members will be able to state distances of objects
within the solar system in terms of light-time, describe the sun as a typical star, relate its share of
the mass within the solar system, and compare the terrestrial and jovian planets. You will be
able to describe the environment in which the solar system resides.
Mission Team Leader’s Note: This mission may also be conducted with viewgraph slides
available from the Galaxy Explorers Web Site. Slides will enhance the Galaxy Explorers
understanding and visual experience.
DISCUSSION
Hello, my name is fill in name. Today we’re going to learn about our solar system. The solar
system has been a topic of study from the beginning of history. For nearly all that time, people
have had to rely on long-range and indirect measurements of its objects. In other words, much of
our exploration has been done from right here on Earth. Only in recent decades have we sent
probes to distant planets. Much has been learned in recent years, but many mysteries remain.
The solar system consists of an average star we call the sun, the planets Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes the satellites (or moons) of the
planets, numerous comets, asteroids, meteoroids, and the interplanetary medium like dust and
gas, which permeates interplanetary space. The sun is the richest source of electromagnetic
energy in the solar system. The next closest star is a red dwarf star called Proxima Centauri, or
the North Star. It is a distance of about 4.3 light years. (Each light year is the distance light
travels in a year, at about 186,000 miles per second, or nearly 6 trillion miles per year.)
The Sun
The sun is a typical star. Its spectral classification is "G2 V." G2 basically means it's a yellowwhite star, and the roman numeral V means it's a "main sequence" dwarf star (by far the most
common) as opposed to super giant, or sub-dwarf, etc.
The sun dominates the gravitational field of the solar system; it contains about 99.85% of the
solar system's mass. The planets, which condensed out of the same disk of material that formed
the sun, contain only about 0.135% of the mass of the solar system. Satellites of the planets,
comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%.
Inner Planets
The inner planets are often called terrestrial or rocky planets. They are called “inner” because
they are closer to the sun. They are Mercury, Venus, Earth, and Mars.
Mercury
Mercury is only about one-third the size of the Earth. It is smaller than any other planet except
Pluto. Mercury is very close to the Sun and has no substantial atmosphere. These factors
contribute to the fact that the surface of Mercury has the greatest temperature range of any planet
or natural satellite in our solar system. The surface temperature on the side of Mercury closest to
the Sun reaches 427 degrees Celsius, a temperature hot enough to melt tin. On the side facing
away from the Sun, or the night side, the temperature drops to -183 degrees Celsius. Scientists
have detected a magnetic field surrounding Mercury, though it is not as strong as the field
around the Earth. Scientists theorize that Mercury's field is due to an iron-bearing core or
possibly to the solar winds. Mercury's atmosphere is very thin and is composed of helium and
sodium. The surface of Mercury has been shaped by three processes: impact cratering where
large objects struck the surface resulting in crater formation, volcanism where lava flooded the
surface, and tectonic activity where the planet's crust moved in order to adjust to the planetary
cooling and contracting. Mercury does not have any naturally occurring satellites.
Venus
Venus and Earth are similar in size, composition, and mass. They differ in that Venus does not
have oceans or human life, and its temperature during the day reaches 484 degrees Celsius
(about 900 degrees Fahrenheit). The daytime temperature is so hot it could melt lead. The dense
atmosphere is composed of carbon dioxide and sulfuric acid that acts as a greenhouse and traps
the heat. Venus revolves around the Sun in a circular orbit once every 225 Earth days.
Venus rotates slowly on its axis in a clockwise direction, which is referred to as a "retrograde"
rotation because it is the opposite of the other eight planets. A rotation takes 243 Earth days, so
a Venusian day is longer than a Venusian year. What's more, Venus rotates in exactly the
opposite direction of Earth. Earth and most of the other planets turn counterclockwise, from
west to east; but Venus turns clockwise, from east to west.
As with the other inner planets, the surface of Venus has been shaped by impact craters, tectonic
activity, and volcanoes which scientists believe to be ongoing. The volcanic activity is believed
to be the source of the sulfur found in the atmosphere. Venus does not have any naturally
occurring satellites (moons).
Because of its lovely brightness, that object was named after the beautiful Roman goddess of
love: Venus. Venus is the brightest of all the stars and planets in the sky. Only the Sun and the
Moon are brighter. Because of the Sun's brightness, Venus can only be seen just before sunrise
or just after sunset. When it is to the east of the Sun, Venus shines in the evening sky like a
jewel and is called the Evening Star. When west of the Sun, it shines before dawn as the
Morning Star. The ancients thought the Morning Star and the Evening Star were two different
objects. Today, we know that they are one object, not two.
When Venus is on the same side of the Sun as we are, it can be as close to Earth as 23.7 million
miles (that's 38.1 million kilometers). Venus is closer to Earth than any other large object,
except for our own Moon. In 1761, and again in 1874, a rare event called a solar transit occurred
when Venus moved across the disk, or face, of the Sun. By watching this transit of Venus across
the disk of the Sun, astronomers could tell that Venus had an atmosphere that contained clouds.
When we view Venus through a telescope, all we see are its yellowy clouds, even though it is the
planet closest to Earth. For many years this thick cloud cover kept astronomers from learning
much at all about Venus's surface, but that didn't stop them from speculating about the planet.
Because Venus has such a thick layer of clouds, many people thought it must have a lot of water
on its surface. Some scientists even theorized that Venus's clouds might help reflect the intense
sunlight it was subject to because of its nearness to the Sun. They reasoned that such reflection
might even keep Venus's surface from getting too hot. Other scientists of the past, and many
science fiction writers as well, pictured Venus as a young planet and imagined that it looked a lot
like Earth did during the age of dinosaurs. They pictured Venus as a tropical world with warm
oceans and lots of plant and animal life. Some people even looked upon Venus as Earth's twin
since the two planets are about the same size. They were all wrong.
Scientists believe the current conditions on Venus are caused by what we call the greenhouse
effect—called that because it simulates the muggy conditions in a greenhouse. Because Venus is
nearer to the Sun than Earth is, it was always warmer. More of its oceans would have
evaporated, putting more water vapor in the atmosphere. Water vapor traps more of the Sun's
heat, just as in a greenhouse. Eventually, there would be no oceans left, and the temperature
would become as hot as the inside of a furnace. We can't be sure that this is what happened on
Venus. Whatever happened, Earth has been lucky--at least until now. But many people are
afraid that our polluted air will raise the level of carbon dioxide and will cause the same thing to
happen here someday. It's up to us to prevent Earth from becoming another overheated Venus.
Earth
Water and gases were trapped in the rocks but slowly fizzed out to form Earth's vast oceans and
Earth's atmosphere. Even today, gases escape from within our planet. Slowly, the heaviest parts
of the Earth--metals such as iron--settled to the center and melted to form a hot metal core.
Around the core a rocky mantle formed. The mantle is hot enough to be slightly soft, and slowly
moves. The Earth's crust is not solid but is broken into many pieces called plates. These plates
move slowly but steadily, so Earth's face is constantly changing.
Hundreds of millions of years ago, all of Earth's continents were in one supercontinent. We call
this continent Pangaea. Slowly, Earth's moving plates pulled Pangaea apart into the seven
continents, as we know them today. Where the plates pull apart, hot rock comes up from
beneath and forms mountains in the middle of ocean floors. The largest mountain range on Earth
lies under the middle of the Atlantic Ocean. Sometimes the tops of the mountains are visible
above the ocean. We call these mountaintops islands. If measured from their underwater bases,
the Hawaiian Islands are the tallest mountains on Earth. Just as the plates are pulling apart in
some places, they must come together in other places. This collision of plates can cause the
crust to crumple. Tens of millions of years ago, India bumped into Asia, and the crumpling of the
crust created the Himalaya Mountains. Sometimes the plates rub past one another.
Earthquakes and volcanoes are Earth's way of adjusting to changing pressures at and below its
surface. But these things can have terrible results, destroying homes and killing hundreds or
even thousands of people.
Earth's amazing gaseous atmosphere is responsible for making life possible on this, the third
planet from the Sun. Our atmosphere contains water vapor which helps to moderate our daily
temperatures. Our atmosphere contains 21% 0xygen, which is necessary for us to breathe, 78%
nitrogen, and .9% argon. The other 0.1% consists of water vapor, carbon dioxide, neon, methane,
krypton, helium, xenon, hydrogen, nitrous oxide, carbon monoxide, nitrogen dioxide, sulfur
dioxide, and ozone. These latter elements are important to have because they help to absorb
harmful solar radiation before it can reach the surface of the Earth. If present in larger amounts,
most of these latter elements would be poisonous to humans. The atmosphere protects us from
meteors as well. Due to the friction generated between a meteor and the atmospheric gases, most
meteors burn up before hitting Earth's surface as a meteorite.
Mars
If we left the Earth,.....and flew off away from the Sun,......Mars would be the first planet we
come to. Mars is much smaller than Earth--it's only half as wide and just one-tenth as massive.
Mars is colder, too, because it is farther from the Sun. Yet of all the planets in our solar system,
Mars is most like the Earth. A day on Mars lasts twenty-four and one-half hours, about the same
length as a day on Earth.
The orbit of Mars around the Sun is extremely elliptical. Because the distance between the Sun
and Mars varies, temperatures range from -125 degrees Celsius in the Martian winter to 22
degrees Celsius in the Martian summer. The Martian atmosphere is composed of over 95%
carbon dioxide. Solar winds carry the thin, weak atmosphere away because Mars has a weak
gravitational and magnetic field. At the Martian poles are polar ice caps that shrink in size during
the Martian spring and summer. The Martian surface is covered by various rocks and a soil that
is rich in an iron-laden clay. The presence of iron explains the planet's reddish-orange
appearance. Mars contains highlands that occur in the southern hemisphere and are composed of
the oldest, most heavily cratered crustal material. Mars also contains lowlands that are found in
the northern hemisphere.
And Mars's axis is tipped so that it has seasons like Earth's. For a long time, people looked at
Mars and wondered if it had living creatures. If so, what were they like? In 1877, Percival
Lowell, an American astronomer, thought he had the answer. He thought that Mars was
inhabited by intelligent beings. Lowell studied narrow, dark markings that had been found on
Mars. He thought these were canals, dug by intelligent Martians that brought water from the
icecaps to the desert areas of Mars. Many people agreed.
Lowell was wrong and Mars turned out to be a dead world. It has many craters like those on the
Moon, and its atmosphere is only 1/100 as thick as Earth's. The "canals" that Percival Lowell
had seen were probably optical illusions. There are, however, deep canyons and large peaks that
are inactive volcanoes. The reddish peaks of Mars would tower above Mount Everest.
The Mars's atmosphere has almost no oxygen and that its surface is as cold as Antarctica or
colder. The Viking probe also found strange markings that look like dry river channels. Perhaps
in the past Mars had liquid water forming rivers and lakes. In that case, what happened to the
water? Is it now frozen in the soil? We believe so.
Traces of carbon and water have also been detected on the two moons, or satellites, of Mars.
Compared to the moon that orbits the Earth, which is a large globe, the moons of Mars are small
and shaped like potatoes. Phobos is 17 miles (or 27 kilometers) across at its longest; and
Deimos, the other moon, is only 10 miles (or 16 kilometers) across. Visitors to Phobos or
Deimos would see Mars looming large and red.
Future probes will collect samples of Mars's soil and send them back to Earth. Then we can test
this soil in great detail. We could even learn more if spaceships carried astronauts to Mars. This
would not be easy, for it might take around two years to make the trip. Perhaps the world could
work together to send people to Mars. They could explore our mysterious neighbor and study its
craters, volcanoes,......canyons, icecaps,... ...glaciers,... ...and whatever else they find. After we
visit Mars, we will be able to form colonies there. Imagine domed cities on the surface. The
early Mars settlers might even be able to make the planet more like Earth. Maybe large supplies
of water can be brought in from the asteroids or from the Martian soil itself.
If the right gases are added, the Martian atmosphere can be changed to grow warmer and to have
air that we can breathe. It may take many, many years, but perhaps this mysterious neighbor can
someday become......a little Earth.
Asteroids
The solar system has a millions of rocky and metallic objects that are in orbit around the Sun but
are too small to be considered full-fledged planets. These objects are known as asteroids or
minor planets. Most, but not all, are found in a band or belt between the orbits of Mars and
Jupiter. Some have orbits that cross Earth's path, and there is evidence that asteroids have hit
Earth in the past. One of the least eroded, best preserved examples of this is the Barringer
Meteor Crater near Winslow, Arizona.
Asteroids are material left over from the formation of the solar system. One theory suggests that
they are the remains of a planet that was destroyed in a massive collision long ago. More likely,
asteroids are material that never coalesced into a planet. In fact, if the estimated total mass of all
asteroids was gathered into a single object, the object would be only about 1,500 kilometers (932
miles) across‹less than half the diameter of our Moon.
Much of our understanding about asteroids comes from examining pieces of space debris that
fall to the surface of Earth. Asteroids that are on a collision course with Earth are called
meteoroids. When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk
of space matter to incinerate in a streak of light known as a meteor. If the meteoroid does not
burn up completely, what's left strikes Earth's surface and is called a meteorite. One of the best
places to look for meteorites is the ice cap of Antarctica.
Of all the meteorites examined, over 90 percent are composed of silicate (stone), and about six
percent are composed of iron and nickel; the rest are a mixture of the three materials. Stony
meteorites are the hardest to identify since they look very much like terrestrial rocks.
Since asteroids are material from the very early solar system, scientists are interested in their
composition. Spacecraft that have flown through the asteroid belt have found that the belt is
really quite empty and that very large distances separate asteroids.
Outer Planets
Jupiter
Jupiter is a large gas planet whose rapid rotation causes the planet to flatten at the poles and
bulge at the equator. Jupiter emits twice as much heat as it absorbs from the Sun, which indicates
it has its own internal heat source. Astronomers estimate the core temperature at 20,000 degrees
Celsius, approximately three times greater than the temperature of the Earth's core. The planet's
powerful magnetic field is thought to be generated by the electric currents produced by
pressurized hydrogen in the mantle. Jupiter's atmosphere is thought to be composed of hydrogen,
helium, sulfur, and nitrogen. Clouds in the atmosphere move in alternating bands from east to
west or west to east. Lightning, more powerful than any that has been experienced on Earth, has
been noted in Jupiter's atmosphere. Also in Jupiter's atmosphere are oval features that are
thought to be circular winds. The most prominent of these is the Great Red Spot, a hurricanelike storm that has been seen in Jupiter's southern hemisphere since Jupiter was first discovered.
Jupiter has at least sixteen natural satellites (and may have over 28) . One of these satellites, Io,
is volcanically active. Instruments aboard the space probe Galileo have detected surface
temperatures on Io higher than any other planetary body in our Solar System. Voyager 2, also a
space probe, has confirmed that Jupiter is surrounded by a system of thin rings. The majority of
the rings are made up of very small particles thought to be debris from meteoroid collisions.
Saturn
Saturn is a large gas planet with an atmosphere composed of hydrogen and helium. Saturn's rapid
spin tends to flatten out the poles while causing a bulge at its equator. The winds in Saturn's
atmosphere reach speeds up to 1800 kilometers per hour! Astronomers see large white spots (or
clouds) on Saturn, which they believe, are storms. Just like Jupiter, Saturn emits twice as much
heat as it absorbs from the Sun indicating it also has an internal heat source. Saturn has an
extensive ring system that is formed by a thousand individual rings. The rings appear to contain
water ice and dust. The thickness of the rings ranges from 10 to 100 meters and the rings vary in
brightness. There are gaps between some rings, while other rings appear to be braided together.
Astronomers believe the rings developed from particles that resulted from the break-up of
naturally occurring satellites. The particles in the rings closer to the planet orbit the planet at a
faster speed than the particles in the rings farther from the planet. There are satellites within the
rings that result in the gaps that are present between some rings. As with Jupiter, the pressurized
hydrogen in Saturn's mantle produces electric currents that create a strong magnetic field around
the planet. Saturn has at least 18 naturally occurring satellites.
Uranus
Uranus is unique in our solar system because it is tilted 98 degrees. When viewed from Earth, it
appears to rotate on its side! At different times throughout its orbit, we can actually view one of
the planet's poles head-on. The atmosphere is composed of hydrogen, helium, and methane. The
temperature in the upper atmosphere is so cold that the methane condenses and forms a thin
cloud layer that gives the planet its blue-green appearance. The winds on Uranus blow mainly to
the east and can reach speeds up to 600 kilometers per hour. The rapid spin of Uranus influences
the winds in the atmosphere. Uranus has a very strong magnetic field. This planet has a system
of rings that was not discovered until 1977. The ring system contains eleven dark rings
composed of varying sized particles. Satellites embedded in the rings create gaps between the
rings. Uranus has at least 20 natural satellites, both within the rings and outside of the rings.
Neptune
From the data collected, we know that Uranus and Neptune are very similar in composition.
Neptune has a mantle of liquid hydrogen while the atmosphere is a combination of ammonia,
helium, and methane. In the upper atmosphere, methane freezes and forms an ice cloud which
casts a shadow on the clouds below. Neptune has bands in its atmosphere where wind speeds
may reach 2000 kilometers per hour! Neptune has large, dark ovals on its surface which
astronomers believe are hurricane-like storms. Neptune generates more heat than it absorbs from
the Sun, indicating it has its own internal heat source. Neptune has a very strong magnetic field.
It also has a ring system consisting of four rings; two thin and two thick. The rings are composed
of dark particles that vary in size. Neptune has eight natural satellites, four of which orbit within
the rings. The largest satellite is Triton. Due to Triton's retrograde orbit, its density, and its
composition, astronomers theorize that Triton was not originally a satellite of Neptune. They
theorize that Triton was captured by Neptune's gravitational pull, forcing it into an orbit around
the planet. Triton is thought to be a combination of rock and ice. Its surface temperature is -245
degrees Celsius, and it has a thin atmosphere of nitrogen and methane.
Pluto
Pluto is tilted 122.5 degrees on its axis. It has an extreme elliptical orbit. Because of the shape of
Pluto's orbit, it actually slips inside of Neptune's orbit once every 248 Earth years for a period of
twenty years. Pluto has one natural satellite, Charon, which is half the size of Pluto. Because
Pluto and Charon are comparable in size, many scientists consider them to be a double planet
(but many scientists don't consider Pluto a planet at all!). Studies conducted using a spectroscope
have detected methane frost on Pluto and water frost on Charon. Like Triton, Neptune's satellite,
Pluto has an atmosphere of nitrogen and methane. Pluto's atmosphere appears to extend out to
include Charon, which suggests that they may share an atmosphere. Through the Hubble Space
Telescope, Charon appears to be bluer in color than Pluto. During the time in its orbit when Pluto
is farthest from the Sun, its atmosphere condenses and falls to the surface as frost.
Distances Within the Solar System
The most common unit of measurement for distances within the solar system is the astronomical
unit (AU). One AU equals the mean distance from the sun to Earth, roughly 150,000,000 km.
Another way to indicate distances within the solar system is terms of light time, which is the
distance light travels in a unit of time. Distances within the solar system, while vast compared to
our travels on Earth's surface, are comparatively small-scale in astronomical terms. For
reference, Proxima Centauri (the North Star), the nearest star at about 4 light years away, is over
265,000 AU from the sun.
Light Time
3 seconds
3 minutes
8.3 minutes
1 hour
11 hours
1 year
4 years
Approximate Distance
900,000 km
54,000,000 km
149,600,000 km
1,000,000,000 km
80 AU
63,000 AU
253,000 AU
Example
~Earth-Moon Round Trip
~Sun to Mercury
Sun to Earth (1 AU)
~1.5 x Sun-Jupiter Distance
Voyager-1 (April, 2001)
Light Year
~Next closest star
Mission Team Leaders Notes: A choice of several activities is available.
ACTIVITIES
RESOURCES/MATERIALS: Maps of the community, state, country, and world, a globe, an
illustration or model of the solar system, a spring scale, various objects to be weighed, string,
pencils, and paper.
1. By using a series of maps, you can help the Galaxy Explorer visualize the enormity of the
universe. Start with a map of the community and continue with a state map, then a map of the
country, a globe of the world, and finally an illustration of the solar system.
2. To help the Galaxy Explorers learn the positions of the planets, make up a phrase using the
first letter of each planet's name in the order of their distances from the sun. For example: "My
Very Educated Mother Just Sat Upon Pink Nests" (Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus, Neptune, Pluto). Note that until 1999, the orbit of Pluto was closer to the sun than that
of Neptune.
3. Let the Galaxy Explorers act out the parts of the sun and the Earth. Have them demonstrate
the rotation of the Earth and its revolution around the sun.
4. Galaxy Explorers can use colored Styrofoam balls to construct a model of the solar system.
Have the Galaxy Explorers choose a planet, research the planet, and then present this
information to the other Mission Team members. At this time, the Mission Team can make a
living model of the solar system. They can write information about the planets on the models.
Mission Teams can also make 3D models out of clay or salt dough or other model material.
Hang the model from the ceiling.
5. The Mission Team can use a spring scale to measure the gravitational pull or weight of
several objects. They can compare the gravitational pull and construct a chart of their results.
6. Draw, color, and label "scale" pictures of the planets. Jupiter is about 11 times bigger than
Earth. Scale means that Jupiter's picture is about 11 times bigger than Earth's. Use rulers, a
compass, or measured string to draw circles in the following sizes
Name
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Diameter
1
3
3
1 1/2
33 1/2
28 1/2
12
11 1/2
½
Radius
1/2
1 1/2
1 1/2
3/4
16 3/4
14 1/4
6
5 3/4
1/4
If you’re feeling adventurous you can try some of Solar System’s larger moons as well.
Name
Ganymede
Titan
Callisto
Io
Moon
Europa
Triton
Charon
Planet
Jupiter
Saturn
Jupiter
Jupiter
Earth
Jupiter
Neptune
Pluto
Diameter
1
1
1
1
1
1/2
1/2
1/2
Radius
½
½
½
½
½
¼
¼
¼
This Mission Plan is largely the work of volunteers supporting NASA Goddard Space Flight Center’s Starchild
program. Acknowledgement is made to the primary authors Joyce Dejoie (left) - Teaches 6th grade science and
gifted math classes at Lakeside Middle School in Evans, GA. She holds a BA in psychology from UCLA and
Master and Specialist in Education degrees from Augusta College (now Augusta State University). Proir to
relocating in Georgia, Mrs. Dejoie taught 5th grade at Union School and English as a Foreign Language at the
Haitian American Institute in Port-au-Prince, Haiti. In addition to volunteering her time to co-author StarChild, she
is an avid reader, student of foreign languages, theater-goer, and traveler. She also spends tremendous amounts of
time seeking Snickers bars and misplaced reading glasses!
Elizabeth "Libby" Truelove (right) - Teaches 8th grade science at Dickerson Middle School in Marietta, GA. She is
also a veterinarian. She graduated from the University of Tennessee College of Veterinary Medicine in 1985. She
received her teaching credentials from Paine College in 1998. She was chosen as Lakeside Middle School and
Columbia County Teacher of the Year for 1999-2000. Dr. Truelove likes to travel, read, attend concerts, and shop
for pieces to add to her Dickens Village Collection. She also enjoys long walks with her dogs and taking
photographs. She has a daughter, Randi, of whom she is proud, and a husband, Jim, who is a font of creative ideas.
He is especially proud of his "Mathy Way" contribution to StarChild.