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The Solar System

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[edit] Introduction

Wikijunior books welcomes you to the children's book "Solar System". Outer space is perhaps the final frontier for man. Even though the rest of the solar system objects may seem like tiny dots from Earth, our celestial neighbors are still important to learn about. The importance of this task has led many experts here at Wiki to donate their time and talents to bring this volume together.

Wikibooks is a project of the Wikimedia Foundation, aimed at providing free, easily available, quality reading for adults and children to promote the global spread of knowledge. Traditional publishing houses make the bulk of their income from re-issues of classic books, new books by authors with long track records, or celebrities who are famous in their own right. The chances of a truly good new work being published solely on the basis of merit skyrocket when the traditional business model is overturned and the wellspring of new talent out there is tapped using the 'net.

With this project we have reached a crossroads between the books of yesterday and the encyclopedia of everything for tomorrow. Simply by reading this book and telling your friends about it, you have advanced the cause of free access to information and of democratizing the field of publishing. Thank you, and once again, welcome.

[edit] What is in the night sky?

What is up there in the sky? During the day, you can often see puffy clouds floating high in the air, and a huge ball of gas called the Sun. But when you look up on a cloudless night, you can see other things up there: the Moon and many, many stars. What are they? How many are there? How large are they? Can I touch them? These are only some of the questions human beings have pondered in the past and continue to ponder.

People have invented telescopes to see these planets and stars better. Stars are very hot balls of gas. Planets look like stars to the naked eye, but if you look at them every night for a month or so, you will notice how they move across the sky. That is because they are moving in their orbit around the sun, just like Earth! There are eight major planets in our solar system: Mercury, Venus, Earth, and Mars are the inner planets; Jupiter, Saturn, Uranus, and Neptune are the outer planets. There are also smaller objects in the outer regions call "dwarf planets". These include Pluto.

[edit] How is the Solar System measured?

When we look at things in the Solar System, we try to measure what we see. This allows us to compare the many objects and to know how and where they will move. To make it easy to share what we know with each other, a common method is used. Most of the world now measures the Solar System using the metric system. This system is a set of values that can be used to measure everything.

In this book, all of the measured values are in the metric system. This was first used in Europe during the eighteenth century. It was meant to replace all of the older systems of measuring things, such as the English system that used units such as feet, inches, pounds, and degrees Fahrenheit. The use of the metric system has made it much easier for people to agree on common sizes for things that are sold and to share information.

The types of values that are shown in this book are length, mass, temperature, and time. Length is used for values such as the size of a planet or the distance of a moon from a planet. Mass can be thought of as the weight of something if it was on the surface of the Earth. So if you weigh 30 kilograms on Earth, your mass is 30 kilograms. If you went somewhere where there was no gravity you would weigh nothing at all, but you would still have a mass of 30 kg. So the weight measures the pull of gravity on something with a given mass.

In the metric system, the length of something is measured in metres. A typical adult is about 1.7 metres high. One metre, in the old English system, is a little longer than 3 feet, 3 inches. The metre is sometimes shortened to an m. 'Metre' is spelled 'meter' in the United States.

For longer distances, the kilometre is used ('kilometre' is spelled 'kilometer' in the United States). A kilometre is a thousand metres. In the old English system, a kilometre is equal to about five-eighths of a mile. It is often shortened to km.

Mass is usually measured in grams. A thousand grams is called a kilogram. The kilogram is often shortened to kg. In the old English system, a kilogram is equal to about 2.2 pounds.

Finally, the temperature of something is measured in degrees Celsius. A degree is sometimes written as a little circle to the right of a temperature value. So 25° means twenty five degrees. The Celsius scale is based upon the temperatures at which water freezes and boils. At 0° Celsius, water at the surface of the Earth will freeze. When the temperature reaches 100° Celsius, water will begin to boil. Celsius is often shortened to C.

[edit] Introduction for Parents, Guardians, and Educators

The Solar System is a Wikijunior book written by a group of volunteers and made freely available to Internet users, printers, and distributors under the terms of its license. It is the result of cooperation between The Beck Foundation, The Wikimedia Foundation, and volunteer writers and editors.

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Next Topic: Solar System

[edit] Solar System

Template:Robert Horning Do you ever wonder about the things in the sky—the Sun, the Moon, the stars? People have been watching the sky for a long time, trying to figure out what is out there. We keep coming up with new ways to learn more about outer space.

Planets are big balls of rock or gas that move around stars. We live on one we call the Earth, which moves around a star we call the Sun. There are at least seven other planets moving around the Sun and a lot of other smaller things as well. All these things together are called a system. The Latin word for the Sun is Sol, so we call this system the Solar System.

A long time ago, people didn't realize that all these things in the Solar System move around the Sun. They thought everything moved around the Earth, including the Sun. This seems sensible, because the Earth doesn't feel as if it's moving, does it?

About 500 years ago, however, a man named Copernicus suggested that all the planets moved around the Sun.^[1] Then, about 100 years later, a man called Galileo began looking at the sky with a new invention: the telescope. He showed that it was very likely that all the planets moved around the Sun. Soon, more and more people started using telescopes to study the sky. They began to learn how the planets and the other things in the Solar System moved.^[2]

Now, we send rockets into space to learn more. Astronauts travel around the Earth. Some of them have landed on the the Moon. Robots can fly to other planets to take pictures. We can see things that people like Copernicus and Galileo could only dream about.

We can use very large telescopes to see what has happened to other stars. We compare pictures of distant stars with pictures of the Sun. We can use thousands of pictures of the planets to learn more about Earth. We use what we learn about all the things in the Solar System to figure out how it was formed. We can also guess what might happen to it in the future.

[edit] What is in the Solar System?

At the center of the Solar System is the Sun. It is a star, like the billions of other stars in the sky. The other stars are very, very far away, so they look tiny. The Sun is important to us because it gives us heat and energy that allows life. None of the life on Earth could exist without the Sun.^[3]

The rest of the things in the Solar System orbit (travel around) the Sun. The planets are the largest of these. Each planet is a little like the Earth. But the planets are also very different from each other.

Many of the planets have moons. A moon orbits a planet. Mercury has no moons.^[4] Earth has one. Jupiter has 63!^[5]

The planets closest to the Sun are called the inner planets. These are Mercury, Venus, Earth, and Mars. Then comes a big ring of asteroids, chunks of rock much smaller than planets. This ring is called the asteroid belt. Within the asteroid belt, there is a dwarf planet named Ceres. Then come the outer planets: Jupiter, Saturn, Uranus, and Neptune. Farther out there are two dwarf planets, Pluto and Eris.

Beyond the orbit of Neptune is another big ring of things like the asteroids, called the Kuiper belt. Kuiper (said "KYE-per") was the last name of the person who first wrote about it. Most of the things in the Kuiper belt are hard to see through telescopes.

After the Kuiper belt comes the Oort cloud. Scientists think this is where comets come from. It is very far away, many times farther away than Pluto is from the Sun (over a thousand times). It is near the edge of the Solar System.^[6] (Yes, "Oort" was the last name of the person who first wrote about it.)

In between all the other things is dust. The pieces of dust are very far apart, but they shine in the light of the Sun. Before dawn, in September or October, they glow in the East. We call this the zodiacal glow.^[7]

When pieces of space dust hit the Earth's atmosphere, they burn brightly. We call them shooting stars or meteors.

The Sun creates solar wind—a kind of gas that blows away from the Sun into space. This gas travels out past the planets into outer space. The edge, where the solar wind meets the wind from other stars, is called the heliopause. That is about 100 times as far from us as the Earth is from the Sun.^[8] Beyond that is a lot of empty space. The nearest star to our Sun is thousands of times farther away than the size of the entire solar system. The Universe is a really huge place!^[9]

[edit] What holds it together?

Why do all of the planets orbit the Sun? Why do moons orbit planets? Why doesn't the Sun move off and leave the planets behind? The answer to all of these questions has to do with gravity. Gravity is a force that is a property of mass. It pulls things together.

We don't notice the pull from the Sun because it also pulls on the Earth by the same amount. But the Sun's gravity is strong enough to keep the Earth from shooting away. Even though the Earth is going fast, it keeps turning to go around the Sun. It is like they were tied together with an invisible string. In the same way, moons orbit many of the planets. They are kept there by gravity. The Sun itself does not sit still in space. The entire Solar System is orbiting the center of our galaxy. The whole thing stays together because of the force of gravity^[10].

[edit] About mass

Everything is made out of matter. The amount of matter is called mass. Two bananas have twice the mass of one banana. The more mass a thing has, the more gravity pulls it and the more its gravity pulls other objects. We don't notice the pull from a banana because it is so much less than the pull from the Earth. If you stand on the ground and let go of a banana, gravity will pull it down towards the center of the Earth. It will hit the ground. If you could throw the banana hard enough at the right angle, it would go into orbit around the Earth. That is how rockets put astronauts into orbit. If you threw the banana really, REALLY hard in the right direction, it would fly away from Earth and never come back; but our arms are not that strong.

The force of gravity from anything is strongest very close to that thing, and weaker further from it. Scientists use weight to mean how hard gravity pulls us. Astronauts weigh less on the moon because it has less mass. It does not pull as hard. We actually weigh a tiny bit less on top of a tall mountain than we do in a lower place. This is because we are farther from most of the Earth.^[11]

[edit] Who discovered the Solar System?

Anyone who looks up at the sky enough can see seven bright objects. These are the Sun, our Moon, Mercury, Venus, Mars, Jupiter, and Saturn. People have known about them for a very long time. Ancient people thought they were related to gods. In Babylon, they named the days of the week after them. Almost everyone was sure that all these things were orbiting the Earth. They did not know we lived in a Solar System.

In 1543, Nicholaus Copernicus figured out that the planets orbit the Sun. Only the Moon orbits the Earth. But he was afraid to say so for most of his life^[12]. Then Galileo Galilei pointed a telescope at the sky. He found moons orbiting Jupiter. He was certain Copernicus was right, and he got in trouble for saying so. It took seventy years to convince scientists that the planets orbit the Sun^[13]. Now, almost everyone on Earth understands that we live in a Solar System.

People made better telescopes and found more things in the sky – moons^[14], new planets^[15], and asteroids^[16]. More things, like the dwarf planet Eris, are being found today.^[17]

[edit] How have we explored the Solar System?

The Sun's image shines on a sheet of paper in 1625. Never let the Sun shine in your eyes

The Voyager 2 space craft.

Before the telescope, people explored the sky with their eyes. They saw how the planets seemed to "wander" through the sky. They learned to predict where the Sun, the moon, and planets would be in the sky. They built some observatories -- places for watching the sky. They watched the Sun and stars to tell the time of year. In China, they even knew when the moon would block the Sun^[18]. Most people thought that celestial bodies could cause war or peace on Earth.^[19]

After telescopes were first made, people kept making them better. Astronomers saw that planets are not like stars. They are worlds, like the Earth. They could see that some planets have moons.^[20] They began to think about what these worlds were like. At first, some thought that the other planets and moons had people or animals living on them. They thought about how it would be to live on these other worlds.^[21] Then they made telescopes better and saw that there are no plants or animals on the Moon^[22] or on Mars.^[23]

Now, we can explore by going to some of the other worlds. Twelve Astronauts walked on the Moon about 35 years ago. They brought rocks and dirt back to Earth.^[24] Spacecraft flew by Venus, Mars, and the outer planets. The pictures they took showed us a lot of what we know about these worlds.^[25] Robots landed on Mars in 1971, 1976, and 1997. They took thousands of pictures of the planets. Two robots, "Spirit" and "Opportunity", are working on Mars right now. They send photos and movies back to Earth. They also check rocks to find out what the rocks are made of.^[26]

So far, we have not found any life except on Earth. Maybe tiny one-celled life once lived on Mars. Maybe there is life under the ice on Jupiter's moon Europa. New spacecraft are being planned to look for life on these worlds.^[27]

[edit] How was our Solar System formed?

Our Solar System is part of the Milky Way galaxy. Galaxies are big mixes of dust, gas, stars, and other things. Inside our Milky Way galaxy are clouds of dust and gas where stars are born. Our Solar System was created in this kind of cloud. A part of the cloud began to get smaller and less spread out. It formed a big, spinning disk of gas and tiny pieces of dust. This disk was thickest at the middle. The middle slowly collapsed until it became the Sun. We are still trying to learn how the planets were formed. Most scientists think that they were formed from the left over gas and dust.

The Sun and planets start to form out of a disk of dust and gas.

This is how it could have happened. The rest of the disk continued to spin around the Sun. The tiny pieces of dust hit each other and some of them stuck together, next the bits of dust slowly collected to form grains, these in turn joined to form lumps the size of gravel, then pebbles, and then rocks. The rocks crashed together into mountains. The mountains crashed together to make bigger things. These big things swept up most of the rest of the disk to form the planets, moons, and asteroids.^[28]

The Sun got hotter as it collapsed. It began to glow. The temperature at the center reached a million degrees. The Sun started to make a lot of light and heat. This light and heat swept away most of the leftover dust and gas between the inner planets. This light and heat are the sunlight we see and feel every day on Earth. ^[29]

[edit] What will happen to the Solar System?

In another five billion years, the Sun will use up most of its hydrogen fuel. It will enter the final stages of its life. The middle of the Sun will shrink down and become even hotter. The outer layer of the Sun will grow much bigger than it is now. It will form a red giant.

It will be so big that some of the nearest planets will be inside it. These planets will burn away. Which planets get destroyed will depend on how much mass the Sun has left.^[30] A strong solar wind will blow some of the outer layers of gas away from the Sun. The Sun will have less mass. The Sun’s gravity will be less. All of the planets will move further away from the Sun.^[31]

After it has been a red giant for a while, the Sun will start to burn helium. It will shrink down and will not be a red giant any more. It will use the helium up in about a billion years. Then it will become a red giant once again. More gas will blow away for a few hundred thousand years.

A planetary nebula^{[Note 1]} will form. The nebula could last for a few thousand to a few tens of thousands of years. It will glow in the light of the Sun.^[32]

At the center, the Sun might shrink into a tiny star called a white dwarf. That kind of star is about the size of Earth. It would take about 100 of these white dwarfs, stacked end to end, to be as wide as the Sun is today. The Sun will not have any more fuel to burn. It will have lots of heat left over and will keep getting cooler and dimmer. Then its light will go out in a hundred billion years from now.^[33]

Next Topic: The Sun

[edit] Notes

[edit] References

1. ↑ http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#q21
2. ↑ http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#galileo
   See also Drake, Stillman (translator) (1957). Discoveries and Opinions of Galileo (1610 Letter to the Grand Duchess Christina). Anchor, NY. ISBN 0385092393.
   
3. ↑ http://imagine.gsfc.nasa.gov/docs/science/know_l1/sun.html
4. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mercury&Display=Moons
5. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=Moons
6. ↑ http://solarsystem.nasa.gov/index.cfm
7. ↑ http://www.gsfc.nasa.gov/scienceques2001/20020301.htm
8. ↑ http://antwrp.gsfc.nasa.gov/apod/ap020624.html
9. ↑ "Outside Our Solar System" in http://vathena.arc.nasa.gov/curric/space/spacover.html
10. ↑ "Gravity is the force responsible for keeping the Earth and other planets in our solar system in orbit around the Sun." from Cosmic Glue, http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970108b.html
11. ↑ Definitions of Mass, Gravity, and Weight from http://ksnn.larc.nasa.gov/webtext.cfm?unit=float
12. ↑ http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#q21
13. ↑ http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#galileo
14. ↑ Calinger, Ronald S. "Huygens, Christiaan." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar268300.;
    http://www.nasa.gov/worldbook/huygens_worldbook.html
15. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Uranus
16. ↑ http://solarsystem.nasa.gov/planetselector.cfm?Object=Asteroids
17. ↑ http://www.space.com/scienceastronomy/050729_new_planet.html;
    http://science.nasa.gov/headlines/y2005/29jul_planetx.xml;
    http://www.jpl.nasa.gov/news/news.cfm?release=2005-126
18. ↑ Eclipse2001 museum http://museumeclipse.org/about/history.html
19. ↑ Varadaraja V Raman (2000). Glimpses of Ancient Science and Scientists. Xlibris Corporation. ISBN 073881363X.
    page 339 "The Chaldeans ... were also the first to suspect... that the Sun, the moon, the planets and the constellation of stars, all affect human life and destiny.... These beliefs gradually spread .. to Egypt, China, Greece, India, and Rome, for example ... astrology is still very popular."
20. ↑ http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#galileo
21. ↑ http://vesuvius.jsc.nasa.gov/er/seh/mars.html;
    Sagan, Carl (1973). Mars and the Mind of Man. Harper and Row. ISBN 0060104430.;
    Verne, Jules (1995). From the Earth to the Moon. North Books. ISBN: 1582871035.;
    From the Earth to the Moon on Project Gutenberg -- http://www.gutenberg.org/etext/83;
22. ↑ http://www.space.com/reference/mars/history.html
23. ↑ http://www.hq.nasa.gov/office/pao/History/SP-350/ch-15-4.html (bottom of page)
24. ↑ http://spaceflight.nasa.gov/history/apollo/index.html
25. ↑ http://www.solarviews.com/eng/sc_hist.htm
26. ↑ http://marsrovers.jpl.nasa.gov/home/
27. ↑ http://www.nasa.gov/missions/solarsystem/Why_We_12.html; http://www.infoplease.com/spot/astronomy1.html
28. ↑ http://planetquest.jpl.nasa.gov/science/origins.html
29. ↑ http://rst.gsfc.nasa.gov/Sect19/Sect19_2a.html
30. ↑ Which planets may get destroyed http://www.public.iastate.edu/~lwillson/FuturSun.pdf
31. ↑ Outline of Sun's death http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html
32. ↑ Planetary nebulae http://www.seds.org/messier/planetar.html
33. ↑ Has information on white dwarf stars http://math.ucr.edu/home/baez/RelWWW/tests.html

[edit] Mercury

Contents 1 Introduction 2 What is in the night sky? 3 How is the Solar System measured? 4 Introduction for Parents, Guardians, and Educators 5 Solar System 5.1 What is in the Solar System? 5.1.1 What holds it together? 5.1.1.1 About mass 5.2 Who discovered the Solar System? 5.3 How have we explored the Solar System? 5.4 How was our Solar System formed? 5.5 What will happen to the Solar System? 5.6 Notes 5.7 References 6 Mercury 6.1 What is Mercury? 6.2 How big is Mercury? 6.3 What is Mercury's surface like? 6.4 How long is a day on this planet? 6.5 How long is a year on Mercury? 6.6 What is Mercury made of? 6.7 How much would Mercury's gravity pull on me? 6.8 Who is this planet named after? 6.9 References 7 Venus 7.1 How big is Venus? 7.2 What is the surface like on this planet? 7.3 How long is a day on Venus? 7.4 How long is a year on Venus? 7.5 What is Venus made of? 7.6 How much would Venus's gravity pull on me? 7.7 Who is this planet named after? 7.8 How long would it take people to get there? 7.9 References 8 Earth 8.1 How big is the Earth? 8.2 What is its surface like? 8.3 Why is there life on Earth? 8.4 What about the Earth's moon? 8.5 How long is a day on this planet? 8.6 How long is a year on this planet? 8.7 What is the Earth made of? 8.8 How much does the Earth's gravity pull on me? 8.9 Who is it named after? 8.10 References 9 Moon 9.1 How big is the moon? 9.2 What is the moon's surface like? 9.3 How long is the Moon's revolution? 9.4 How long is a year on the moon? 9.5 What is the moon made of? 9.6 How much would the moon's gravity pull on me? 9.7 Who is the moon named after? 9.8 References 10 Mars 10.1 How big is the planet? 10.2 What is its surface like? 10.3 How long is a day and year on this planet? 10.4 What is it made of? 10.5 How heavy would I be on Mars? 10.6 Who was it named after? 10.7 References 11 Jupiter 11.1 How big is the planet? 11.2 What is the surface like on Jupiter ? 11.3 What are its rings like? 11.4 What are its moons like? 11.4.1 Amalthea Group 11.4.2 Io 11.4.3 Europa 11.4.4 Ganymede 11.4.5 Callisto 11.4.6 Other moons 11.5 How long is a day on this planet? 11.6 How long is a year on this planet? 11.7 How much would Jupiter's gravity pull on me? 11.8 Who is it named after? 12 Saturn 12.1 How big is the planet? 12.2 What is its surface like? 12.3 What are its rings like? 12.4 What are its moons like? 12.4.1 Shepherd moons 12.4.2 Mimas 12.4.3 Enceladus 12.4.4 Tethys 12.4.5 Dione 12.4.6 Rhea 12.4.7 Titan 12.4.8 Hyperion 12.4.9 Iapetus 12.4.10 Phoebe 12.4.11 Other moons 12.5 How long is a day on this planet? 12.6 How long is a year on this planet? 12.7 What is it made of? 12.8 How much would Saturn's gravity pull on me? 12.9 Who is it named after? 12.10 References 13 Uranus 13.1 How big is Uranus? 13.2 What is the surface of Uranus like? 13.3 What are the rings around Uranus like? 13.4 What are its moons like? 13.4.1 Miranda 13.4.2 Ariel 13.4.3 Umbriel 13.4.4 Titania 13.4.5 Oberon 13.4.6 Other Moons 13.5 How long is a day on Uranus? 13.6 How long is a year on Uranus? 13.7 What is Uranus made of? 13.8 How much would Uranus's gravity pull on me? 13.9 Who is Uranus named after? 13.10 References 14 Neptune 14.1 How big is this planet ? 14.2 What is its surface like? 14.3 What are its rings like? 14.4 What are its moons like? 14.4.1 Inner Moons 14.4.1.1 Proteus 14.4.1.2 Triton 14.4.1.3 Nereid 14.4.2 Outer Moons 14.5 How long is a day on this planet? 14.6 How long is a year on this planet? 14.7 What is it made of? 14.8 How much would Neptune's gravity pull on me? 14.9 Who is it named after? 14.10 References 15 Pluto 15.1 How big is Pluto? 15.2 What is its Surface like? 15.3 What are Pluto's moons like? 15.4 How long is a day on Pluto? 15.5 How long is a year on Pluto? 15.6 What is it made of? 15.7 How much would Pluto's gravity pull on me? 15.8 Who is Pluto named after? 15.9 Is Pluto a planet? 15.10 References

[edit] What is Mercury?

Template:Robert Horning/Coolfacts

Mercury is the closest planet to the Sun. It is a terrestrial planet. That means a planet made from rock like Earth. It does not have a gas atmosphere, so there is no weather. For a long time, only one spacecraft, Mariner 10, had visited Mercury. In January 2008, the MESSENGER spacecraft went by Mercury. It will go by Mercury two more times before starting to go around the planet in 2011.

[edit] How big is Mercury?

Mercury is 4879 km across. Mercury's diameter is just less than half the diameter of the Earth. It is the smallest planet in the Solar System. Only dwarf planets like Pluto are smaller. Mercury's small size and its closeness to the Sun sometimes make it difficult to see without a telescope or binoculars. The best time to spot Mercury in the sky is just after the sun goes down at night or shortly before it rises in the morning.

[edit] What is Mercury's surface like?

Mercury has craters like those on the Earth's moon. The largest crater on Mercury is the Caloris Basin. It is about 1300 km wide. It was created by a huge asteroid hitting Mercury. The asteroid was probably 100 km wide, but it hit Mercury's surface so hard that it made a much bigger hole.

Template:Robert Horning The surface also has big cliffs called scarps. They were made long ago when Mercury cooled down. It shrank, causing the surface to get wrinkled in some places. This wrinkling created the scarps.

There may also be ice on the top and bottom of Mercury. Like the Earth, these areas (called poles) don't get much warmth from the Sun. Any ice there won't melt.

It is very hot during the day (over 400°C) because Mercury is so close to the Sun. At night it is very cold because Mercury loses almost all its heat since there is almost no atmosphere to keep the warmth there. The temperature can fall to almost -175°C.

[edit] How long is a day on this planet?

Mercury rotates (spins around) much more slowly than the Earth. It takes Mercury 58 days to spin once. Because Mercury orbits the sun very quickly, a day on Mercury lasts longer than 58 days. If you were standing on Mercury, at the equator and timed how long it took the sun to go from directly overhead to sunset to sunrise and then rise directly overhead again, it would take 176 Earth days. These long days and nights allow for the temperatures to rise as high, and fall as low, as they do.

[edit] How long is a year on Mercury?

Mercury has the shortest year in the Solar System. It is about 88 Earth days long.

It used to be believed that the same side of Mercury always faced the Sun. In order for this to be true, Mercury would have to take the same amount of time to rotate (spin around) as it does to circle the sun. Through careful observation we now know that Mercury's rotation is somewhat faster than its orbit. Because of the way the orbit and rotation work together, on Mercury, a day is actually almost twice as long as a year.

[edit] What is Mercury made of?

The center of Mercury is made of iron in partly-molten (liquid) form. We know that it is iron at the center because the planet generates a magnetic field. It contains more iron for its size than any other planet in the Solar System. The rest of Mercury, its thick crust, is made of a special type of rock called silicate rocks. There are craters near the poles that are constantly in shadow. Some of these craters contain ice. There is a huge crater on Mercury called Caloris Basin. It was formed when a comet hit the planet and lava or molten rock filled the impact crater. The round wall of this crater is over 2km tall.

[edit] How much would Mercury's gravity pull on me?

If you were on Mercury, it would pull you down less than half (38%)as much as the Earth. An item that weighs 100 Newton on Earth, would only weigh 38 Newton on Mercury.

[edit] Who is this planet named after?

In Roman mythology, Mercury was the messenger of the gods. He wore a hat and sandals with wings on them, allowing him to travel around the world very quickly. The planet Mercury was named after him because it moves around the Sun faster than any other planet in the Solar System. It moves nearly 48 km every second!

Next Topic: Venus

[edit] References

NASA's Solar System Exploration[1]
Arnett, Bill. The Nine Planets[2]
Worldbook Online [3]
Worldbook@NASA, "Mercury"[4]
NASA Planetary Fact Sheet [5]
Hamilton, Calvin J. . Solarviews.com, "Mercury" [6]
Encyclopedia Mythica, "Mercury" [7]
Col, Jeananda. Enchanted Learning/Zoom Astronomy [8] 1998-2005
Usborne Internet-Linked Science Encylopedia, Usborne Publishing Ltd. ISBN 0794503314[9]
Dickinson, Terrence. The Universe and Beyond . Firefly Books ISBN 1552093611

[edit] Venus

Venus is the second closest planet to the Sun. It is a terrestrial planet. This means that we think it was created in a similar way to our planet Earth and is made of rock.

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[edit] How big is Venus?

Venus is almost the same size as the Earth. This is one reason why Venus is sometimes thought of as Earth's "twin". Venus has a diameter of about 12,100 km. It has also been visited by many probes.

[edit] What is the surface like on this planet?

The surface of Venus is very different from the surface of the Earth. It is very dry and hot enough to melt lead. The pressure on the surface is very strong. It is the same as being 1 km (3,280 feet) below the surface of the sea on Earth (sort of)

Channels that look like rivers have formed on Venus. Scientists think these channels are formed from erupting lava. The lava flows along as it cools down, creating the channels. One feature only Venus seems to have is unusual volcanoes called arachnoids. These are volcanoes that have formed differently from other volcanoes we have found in the Solar System. We don't know exactly how they were formed. Venus also has volcanoes like those on Earth.

Parts of the surface of Venus look something like continents. The largest of these areas is called Ishtar Terra. Deep basins like those under the Earth's oceans have also been discovered. On Venus, though, they have no water. Features like mountain ranges and meteor craters have also been found on Venus. One of the highest mountains on Venus, Maxwell Montes, is about 11 km taller than Mount Everest, the highest mountain on Earth.

[edit] How long is a day on Venus?

Venus rotates (spins around) even more slowly than Mercury. One full rotation of Venus takes about 243 Earth days. Venus also rotates in the opposite direction to the other planets in the Solar System. One day on Venus, from noon to noon, depends on the length of the year as well as the rotation time, and is about 117 earth days.

[edit] How long is a year on Venus?

One year on Venus is almost 225 Earth days long. This is less time than it takes Venus to rotate on its axis and less than two Venus days. A year is shorter than a day on venus (245 days).

[edit] What is Venus made of?

The surface of Venus, its crust, is covered in rock. The core of Venus is made of nickel-iron. The atmosphere around Venus is very thick and is made of carbon dioxide, nitrogen, and poisonous gasses that create high pressure and trap in heat.

[edit] How much would Venus's gravity pull on me?

If you were on Venus, it would pull you down almost as strongly as Earth. The atmosphere exerts a pressure at the surface more than 90 times Earth's normal sea-level pressure.

[edit] Who is this planet named after?

Venus is named after the Roman goddess of love. Sometimes it can be seen shining brightly just before dawn or just after sunset. Some people like the Aztecs and the Greeks, gave Venus two names – one for the morning and one for the evening.

Because Venus and the Earth are the same size, scientists call Venus "Earth's sister planet". For a long time most scientists thought that Venus had plants, animals, and possibly even people. However because Venus is so hot we now know that it is impossible for anything to live there.

[edit] How long would it take people to get there?

It could take around a year to get there.

[edit] References

Volcano World, "Lava Flows"[10]
Astronomy Picture of the Day [11]
Alder Planetarium[12]
Mount Everest [13]
Windows to the Universe[14]
NASA's Solar System Exploration[15]
Arnett, Bill. The Nine Planets[16]
Worldbook Online [17]
Worldbook@NASA, "Mercury"[18]
NASA Planetary Fact Sheet [19]
Hamilton, Calvin J. . Solarviews.com, "Mercury" [20]
Encyclopedia Mythica, "Mercury" [21]
Col, Jeananda. Enchanted Learning/Zoom Astronomy [22] 1998-2005
Usborne Internet-Linked Science Encyclopedia, Usborne Publishing Ltd. ISBN 0794503314[23]
Dickinson, Terrence. The Universe and Beyond . Firefly Books ISBN 1552093611

Next Topic: Earth

[edit] Earth

Earth is the planet we live on. It is the only planet in the Solar System with liquid water on its surface. It is also the only planet we know to have life on it.

[edit] How big is the Earth?

The Earth is nearly 13,000 km wide. It's the largest terrestrial planet in the Solar System.

The Earth's mass is about 5,973,700,000,000,000,000,000,000 kg. That's a lot. But it is little compared with Jupiter (319 Earths) and tiny compared with the Sun (335,789 Earths) or other stars!

[edit] What is its surface like?

The Earth's surface is made of rock. Most of it is underwater, but not all. Islands of rock rise up out of the water. The biggest islands are called continents, of which there are seven: North America, South America, Europe, Asia, Africa, Australia, and Antarctica. The largest bodies of water are called oceans, of which there are four: Pacific, Atlantic, Indian, and Arctic. Some authorities classify the Southern as a fifth ocean.

The Earth's surface is made up of huge plates. They are like huge jigsaw pieces made of rock. These plates move very, very slowly, carrying the continents with them. They can rub beside each other, push against each other, or even move away from each other. If there are gaps between them, hot molten rock can rise up and make volcanoes. Where the plates rub or push against each other, earthquakes may happen. When two plates push each other's rock upwards, mountains are formed.

Earth has many kinds of environments. It is cold and icy in places like Antarctica. It is hot and dry in deserts like the Sahara in Africa and Death Valley in the United States. It is cold and dry in deserts like Siberia in Russia. Where it is warm and wet, rainforests grow.

[edit] Why is there life on Earth?

Wherever we have looked on Earth, we have found living things. They may be very small, like bacteria, but they are there. We have found bacteria where it is very cold, very hot, very deep, very high or very dark.

What all living things on Earth seem to need is liquid water. Wherever you can find some water, there are almost always living things there too, even if you can't see them. If we find liquid water somewhere else in the Solar System, scientists think we might find some living things there too. If we don't, there is always the rest of the universe to explore!

There is another possibility. All the living things we know need liquid water. But maybe somewhere else there are living things that don't need water. Perhaps we will need to learn how to recognize them.

[edit] What about the Earth's moon?

Earth has one moon we call... the Moon!  Sometimes it is called by its name in Latin, Luna, so we don't get confused with other planets and their moons. The Moon has also been called Selene (pronounced "suh-LEE-nee") which is Greek for moon.

Recently we have also found some other objects that seem to go around the Earth. The largest one, called Cruithne (pronounced "cru-EE-nyuh"), is three miles wide. It orbits (goes around) the Sun in a way that makes it appear to orbit Earth.

When Earth was young, a comet hit Earth and split off a section of the Earth that is now the moon.

[edit] How long is a day on this planet?

A day on Earth is 24 hours long. That's daytime and night time. A 24 hour day is how long it takes the Earth to spin around once. On the half of the Earth that is facing the sun it is daytime and on the half of the Earth that is facing away from the sun it is nighttime.

The spin of the earth is also the reason why the sun appears to rise in the east and to set in the west. Although it looks like the sun is moving from the surface of the earth, it is really the surface of the earth that is moving. The reason we do not feel like we are spinning is because the earth is so big compared to the size of people.

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[edit] How long is a year on this planet?

A year on Earth is about 365 and 1/4 days long. That's how long it takes the Earth to orbit the Sun once. Approximately every four years we have a leap year. A leap year contains an extra day in our calendar on February 29th in order to account for the 1/4 of a day left over each year.

[edit] What is the Earth made of?

When a planet is made of rock, we call its surface the crust. Below the Earth's crust is hot molten rock. It is in a layer called the mantle. The hot molten rock is what comes out of volcanoes. It's then called lava.

Under the mantle is the core of the Earth. We think it is made from solid iron and nickel, surrounded by hot molten iron. The temperature there is very very hot!

The Earth's crust is very thin compared to the mantle and the core. But it is very thick to us. Nobody has drilled all the way through it yet. Even the deepest underground mines are far away from reaching its deepest base.

[edit] How much does the Earth's gravity pull on me?

It's easy to find your weight on Earth by using a scale. You have weight because the Earth's gravity pulls you towards its center. Normally, the ground or the floor get in the way, making you feel 'stuck' to them.

There are several kinds of scales:

1) Comparing of 2 masses (weights). You put the thing(s) you want to weigh on one pan (like some marbles), and then you put several "weights" on the other pan until the pointer shows that both pans have equal weights on them. Then you look at the pan with the known weights on it, and add them all up. The total is the mass of the thing(s) you want to weigh.

2) A spring balance usually has a hook on it, with a pan. You put the thing(s) you want to weigh on the pan, the spring is pulled, and the greater the weight, the further the spring is pulled. That distance, calibrated in pounds or kilogram (or whatever), is usually shown either on a dial or on a linear scale.

3) There are also electronic scales that give a properly calibrated reading—grocery stores, for example, use these.

NOTE: Gravity varies slightly depending on the location where you want to get the weight; spring balances and some electronic scales can, in theory, read slightly different weights at different places because of that, but usually in practice that difference is too small to be noticed. But, because the balance type of scales work differently from the spring or electronic types, they will always read the true, correct mass. They would even give the same mass on the Moon, where gravity is much less than on Earth.

Did you know? that Sir Isaac Newton was the first person to realise that the force pulling you down to the ground was the same force that keeps the planets going around the Sun? The story goes that he thought of this when he saw an apple fall from a tree.

Gravity is a very important force. As well as keeping you firmly stuck to the Earth, it keeps the Moon going round the Earth, The Earth going around the Sun and the Sun going around the center of the Milky Way galaxy. Gravity also makes stars and planets a nice round ball shape. In fact without gravity there wouldn't even be a Sun, Moon or Earth because the material that they are made of would just float away into space.

[edit] Who is it named after?

The word earth is used for both planet Earth and soil. Other names had been used for Earth such as Gaia and Tellus. Gaia is the Greek goddess (meaning Mother Earth). Tellus is the Roman name of the same goddess.

Next Topic: Moon

[edit] References

"It is also the only planet we know..." [24] [25]
"The Earth is nearly..." [26] [27]
"The Earth's mass..." [28]
"Earth's surface is made of..." [29] [30]

[edit] Moon

Template:Robert Horning/Coolfacts

[edit] How big is the moon?

Most of the planets in the Solar System are much bigger than their moons, but the Earth and the Moon are much closer in size. The Moon is just under 3,500 kilometers (km) wide and the Earth is about 12,600 (km). That's only about one third of the size of the Earth as you can see in the picture below. Because of this, the Earth and Moon together are sometimes called a binary or double planet system.
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[edit] What is the moon's surface like?

The Moon does not have any atmosphere. It also doesn't have any liquid water on its surface. During the day it becomes very hot, but at night it is icy cold. A person visiting the Moon needs an air supply and a special suit.

The Moon has many craters on its surface. The largest one is called the South Pole-Aitken Basin and is roughly 2500 km across.

We think nearly all the craters on moons or planets were made by huge rocks hitting them a long time ago. They are called impacts.

Some of the craters on the Moon look as if they have rays coming out of them. These rays are rocks thrown across the Moon by the impacts that made the craters. Some of the craters around the bottom of the Moon may have ice in them.

There are also darker areas called maria (said "MARR-ee-ah"). These are large pools of lava that cooled a long time ago. Most maria are on the side of the Moon we see from Earth. The lighter areas on the Moon are highlands.

[edit] How long is the Moon's revolution?

The Moon takes just over 27 Earth days to rotate (rotate means spin around) once.

[edit] How long is a year on the moon?

The Moon also takes just over 27 days to orbit (move around) the Earth. This is why we always see the same side of the Moon when we look from the Earth. We call this side the near side. The other side we call the far side. In 1959 a probe sent back pictures of the far side. That was the first time anyone saw what it looked like.

[edit] What is the moon made of?

The surface of the Moon is made of rocks and dust. The outer layer of the Moon is called the crust. The crust is about 70 km thick on the near side and 100 km thick on the far side. It is thinner under the maria and thicker under the highlands. There may be more maria on the near side because the crust is thinner. It was easier for lava to rise up to the surface.

We think the Moon has a small core (center) about 300 km across. The core is composed of solid iron. Because the core is solid, the moon does not have its own magnetic field.

[edit] How much would the moon's gravity pull on me?

If you were on the Moon, it would pull you down about a sixth as much as the Earth does, so you'd weigh a sixth as much. So would anything else. That's why it was much easier for the astronauts visiting the Moon to pick up rocks there.

[edit] Who is the moon named after?

The names Moon and month both come from the ancient Greek name for the Moon, Mene. There have been other names for the Moon, like Selene and Luna. Selene was the Greek goddess of the Moon. Luna was the Roman goddess of the Moon. The Roman people also associated their goddess Diana with the Moon.

Next Topic: Mars

[edit] References

"The moon is just under..." [31] [32]
"So the Earth and the moon together..." [33] [34]
"The Moon does not have any atmosphere." [35] [36]
"During the day it becomes..." [37] [38]
"The largest one is called..." [39] [40]
"These rays are rocks..." [41]
"Some of the craters around the bottom..." [42] [43]
"There are also darker areas..." [44] [45]
"The lighter areas..." [46]
"The Moon takes just over 27..." [47] [48]
"We call this side..." [49] [50] [51]
"The other side we call..." [52] [53]
"The surface of the Moon..." [54] [55] [56] [57]
"...it would pull you down..." [58] [59]
"The names "Moon" and..." [60] [61] [62]

[edit] Mars

Mars is the fourth planet from the Sun. It is called a terrestrial planet because it has a rocky surface like the Earth.

[edit] How big is the planet?

Mars is the second smallest of the eight major planets in the Solar System. Only Mercury is smaller. It is nearly 7,000 kilometres (km) wide; just over half the width of the Earth. Its volume is about 15% of the Earth. Since a lot of the Earth is covered by water, the total surface area of the Mars is nearly as large as all of the land on the Earth. It is possible that its size may eventually prevent human colonies.

[edit] What is its surface like?

The surface of Mars is a lot like a desert on Earth; it is very dry and dusty, but it is also very cold. There are a lot of loose rocks and dunes of fine sand. Crater impacts mark the surface, but these are not as common as on the Moon. One of the craters is the huge Hellas Planitia. It is about half the size of the continental United States. The southern half of the planet has more craters than in the north. The south is also higher in elevation.

There is an area on Mars called the Tharsis Bulge, which has four huge volcanoes. These volcanoes have not erupted for millions of years. The largest volcano is called Olympus Mons. It is 27 km tall, making it the highest mountain in the Solar System; much higher than Mount Everest on Earth. It is 625 km across and takes up an area as big as the US state of Arizona. Mars also has a huge canyon called the Valles Marineris. It is much bigger than the Grand Canyon on Earth. It is 4000 km long, up to 7 km deep and up to 200 km wide. Scientists think that when the Tharsis Bulge was created, the surface of Mars cracked to form the Valles Marineris.

Like the Earth, Mars has ice caps at its poles. They are made from ice and frozen carbon dioxide. During the Martian winter, the southern cap grows as carbon dioxide from the atmosphere freezes. The cap shrinks again during the Martian summer.

In some places, there are dry channels that look like they were made by running water. So, a long time ago Mars may have had lakes and streams made of water. Now all of the water is frozen into ice under the surface.

There is an atmosphere on Mars, but it is very thin. There is also much more carbon dioxide in it than oxygen. (Oxygen is the gas we want when we breathe in; carbon dioxide the gas we get rid of when we breathe out.) So, we would need spacesuits to visit Mars. The atmosphere helps protect the surface from smaller meteorites.

When Mars comes closest to the Sun, the atmosphere can stir up storms of dust. Some of these storms are gigantic; they can cover the entire planet in clouds of dust. Dust storms on Mars can last for hundreds of days and reach wind speeds of 200 kilometres per hour. Huge storms like these have been seen from the Earth through telescopes.

Template:Robert Horning Template:Robert Horning/Mars

[edit] How long is a day and year on this planet?

One day on Earth is only 39 minutes and 35 seconds shorter than a day on Mars (1.026 Earth days). A year on Mars is almost two Earth years long (687 Earth days).

Much like the Earth, the axis of rotation of Mars is tilted at an angle. This tilt causes seasons on Mars as it travels around the Sun. Summer occurs on the half of the planet that is tilted toward the Sun, and winter on the other half. After half a Martian year has passed the seasons are reversed. But these seasons are about twice as long as on Earth.

[edit] What is it made of?

The outer, rocky surface of Mars is called the crust. Most of the crust is made from basalt, a type of rock made when lava grows cold.

Like the Earth, Mars has a thick layer of rock below the crust called the mantle. The mantle is much hotter than the crust, and the mantle rock is partly molten. But the crust on Mars has grown thick, so the lava from the mantle no longer reaches the surface. There are volcanoes on Mars, but they are no longer active.

At the center of Mars is a core made of the metals iron and nickel. If Mars were the same size as the Earth, the core of Mars would be smaller then the Earth's core. So a larger amount of Mars is made out of rock. Because rock is lighter than the metals in the core, Mars has a lower density than the Earth.

[edit] How heavy would I be on Mars?

If you were on Mars, you would be lighter, as Mars' gravity only has a force about two fifths as strong as the that of Earth's. You could lift objects that weigh almost three times as much compared to similar objects here on the Earth. You could jump up almost three times higher, and it would take much longer to fall to the ground from the same height.

Even though it looks as though you would be like a comic-book hero on Mars, there are some things you couldn't do. Although a big rock would weigh less and you could pick it up, it would still have the same mass. If you tried to catch it, it would knock you over, and if it landed on you it would crush you. A car on the surface of Mars would need the same amount of power to speed up, although going uphill would be less of a problem. It may, however, need more room to stop. Because of the reduced gravity a vehicle would not "grip" the ground on Mars as strongly, but the constant mass would keep the vehicle moving just as strongly, making it easy to go into a skid.

[edit] Who was it named after?

In Roman mythology, Mars was the god of war and agriculture. The planet Mars was named this because Mars is red like blood.

Next Topic: Asteroid belt

[edit] References

• Steven W. Squyres, Mars, World Book Online Reference Center, World Book, Inc., 2004. [63] [64]
• "a terrestrial planet" [65]
• "How big is the planet?" [66] [67]
• "How long is a day on this planet?" [68] [69]
• "What is it made of?" Steven W. Squyres, ibid.

[edit] Jupiter

Jupiter is by far the largest planet within our Solar System: two and a half times larger than all of the other planets put together. It is the fifth planet from the Sun and one of the brightest planets. Jupiter is sometimes called a "gas giant" because most of this planet is made up of liquid and gas.

[edit] How big is the planet?

Jupiter is 142,984 km or about 11 Earths in diameter at the equator. That makes it about one tenth as big as the Sun! You could fit about 1,400 Earths into the volume of Jupiter. It is 133,709 km or 10 Earths in diameter from pole to pole. Jupiter's rapid rotation makes it bulge out at the equator.

Jupiter's magnetic field is the largest single planetary thing in the Solar System. It is 26 million kilometers across, making it about 20 times bigger than the Sun. It has a tail that extends past Saturn's orbit. If it could be seen from Earth, it would appear to be five times the size of the full moon.

[edit] What is the surface like on Jupiter ?

The surface we see is not solid. This enormous planet has a relatively small solid and rocky core. Liquids and gases surround this core and blend with the atmosphere.

Jupiter is a cloudy, windy and stormy planet. It is always covered by a layer of clouds, and wind speeds of 600 km/h are not uncommon. The storms are visible as swirls, bands and spots. A particularly violent storm, about three times Earth's diameter, is known as the Great Red Spot. This storm has been in existence for nearly 300 years!

The layer of clouds is divided into several bands. The lighter colored bands are called zones and the darker bands are called belts. The colors are caused by small changes in the temperature and chemistry. Each band rotates in the opposite direction from its neighbors. Along the edges where the bands meet, these winds collide and create swirling patterns.

The stormy atmosphere of Jupiter has flashes of lightning just like on Earth. However these can be up to 100 times more powerful. The lightning is made by water near the tops of the clouds.

[edit] What are its rings like?

Jupiter's rings are dark and hard to see. They are made of tiny particles that meteors knocked off Jupiter's small inner moons and debris left over from comets and other objects that came close to the surface of Jupiter. In fact, until the Voyager spacecraft arrived near Jupiter and took closeup pictures of the rings of Jupiter, scientists didn't even know that it even had rings at all. Two rings are clearly from material that can be associated with two sets of the inner moons of the planet.

These are the names of the rings and their sizes:

Rings of Jupiter

Ring Name	Inner Radius	Outer Radius
Halo	100,000 km	122,000 km
Main	122,000 km	129,000 km
Gossamer (inner)	129,000 km	182,000 km
Gossamer (outer)	182,000 km	225,000 km

[edit] What are its moons like?

Jupiter has 63 known moons. There are four major moons that were discovered by Galileo in 1610. Those moons are Io, Europa, Ganymede and Callisto. They are called the Galilean moons. There are often eclipses on Jupiter's cloud tops by the Galilean moons.
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[edit] Amalthea Group

There are four small moons orbiting inside Io's orbit. That group is called the Amalthea group because Amalthea is the largest one. They are all small and potato shaped. Amalthea is very red. The material of Jupiter's rings came from meteors knocking it off of those moons.

[edit] Io

Io (pronounced EYE-oh) is Jupiter's closest major moon. It is 3643.2 km across, slightly larger than Earth's Moon. It has the most spectacular volcanoes in the solar system and molten sulfur lakes. Any craters formed by asteroids hitting the surface are quickly covered up by the volcanic activity. Io's core is made of molten iron and is surrounded by a rock shell. Unlike Jupiter's other moons, there is very little water on Io. Scientists think that when Jupiter was forming, it was hot enough to dry out Io, but not the other major moons. In Roman mythology, Io was a beautiful young woman that Jupiter loved.

[edit] Europa

Europa is 3,121.6 km across, about ten percent smaller than Earth's Moon. It is made of silicates and has a layer of smooth water ice 10 to 30 km thick. The ice has long cracks in it and very few craters. It looks like the sea ice on Earth. The ice had slid around at the cracks. There is liquid water under the ice up to 100 km below the surface. There are also some large spots on the surface. In Roman mythology Europa was courted by Jupiter in the form of a bull.

[edit] Ganymede

Ganymede is 5262.4 km across, making it 380 km wider than Mercury. It is Jupiter's largest moon and the largest moon in the Solar System. It had plate tectonics like Earth. There are older, darker regions and newer areas with grooves where the plates have moved. Newer craters have bright rays around them from material thrown up by impacts. Older craters look flat and faded because the icy surface does not hold the shape of the crater as well as rock does over long periods of time. Ganymede may have an iron and sulfur core with a silicate mantle and an icy shell. It may be like Io except with a layer of ice on it. In Roman mythology Ganymede was a beautiful young man who Jupiter kidnapped and made cupbearer to the gods on Mt. Olympus.

[edit] Callisto

Callisto is 4820.6 km across, about the same size as Mercury. It has many craters. Like craters on Ganymede, the older craters had faded. The largest crater is Valhalla. It has a bright center 600 km across with rings around it up to 3000 km across. Callisto is made of silicates and ice. There is a 200 km thick icy crust with a liquid water sea under it. In Roman mythology Callisto was turned into a bear by Jupiter's jealous wife Juno. Later Jupiter placed her in the stars as The Great Bear.

[edit] Other moons

The other moons are tiny ones in several groups outside the orbits of the major moons, there is a small moon, Themisto and four groups of little moons that orbit very far from Jupiter.

[edit] How long is a day on this planet?

One Jupiter day is about 10 Earth hours long. You have to say "about" because different parts of Jupiter rotate about its axis at different speeds. This is caused by the fact that Jupiter is mostly gases that are in constant motion and sometimes going in opposite directions. Some efforts have been made to try and measure the rotation speed of the inner rocky core of Jupiter, but that has proved to be quite difficult to accomplish due to the magnetic fields that surround Jupiter and the very active radio energy that is generated by the atmosphere of Jupiter, which interferes with measuring techniques like radar that has been used to measure the surface of Venus and Mars.

[edit] How long is a year on this planet?

One year on Jupiter is 4,335 Earth days or 11.87 Earth years long.

A Jupiter year is about equal to four-tenths (or two-fifths) of a Saturn year. Thus after every two Saturn years, Jupiter has completed five full orbits about the Sun. So after 59 years, Saturn and Jupiter will be back in nearly the same position. When the orbits of two planets are simple ratios of each other like this, it is called a resonance.

[edit] How much would Jupiter's gravity pull on me?

If someone were floating close to the cloud tops of Jupiter, it would pull them down with a force about two and a half times as strong as the force of Earth's gravity.

Jupiter's rapid rotation causes the equator to bulge out. This would also cancel out about 10 percent of gravity's force on them if they were at the equator. The amount of this counteraction becomes lower the closer they get to the poles.

[edit] Who is it named after?

Jupiter is named after the chief of the Roman gods, also called Zeus in ancient Greece. It was so named because of the planet's enormous size, which dominates all the others.

Next Topic: Saturn

[edit] Saturn

Saturn is the sixth planet from the sun, and is a giant gas giant.

Template:Robert Horning

[edit] How big is the planet?

Saturn is 120,536 km or 9.449 Earths wide at the equator.^[1]

[edit] What is its surface like?

Saturn is mostly gas and liquid.^[2] Saturn may have a small core of rock and ice.^[3] The atmosphere has bands, but they are not as colorful as Jupiter's.

[edit] What are its rings like?

Saturn's rings are composed of rock and ice particles ranging in size from specks of dust to the size of a house. Some particles might even be a few kilometers wide! The particles in the rings are actually spaced far apart. It would be easy to pass through the rings.^[4]

[edit] What are its moons like?

Saturn has 56 moons, and many of them have names.^[5]The size of Saturn's moons and the size of the chunks of ice in its rings are similar, which means that we can never know the exact number of moons. ^[6] New moons are still being discovered. Saturn's biggest moon is named Titan, and is large enough to be a planet in its own right!

[edit] Shepherd moons

There are small potato-shaped moons in or near Saturn's rings. They control the ring particles with their gravity. That is why they are called shepherd moons. Six of them are known, and there may be more.^[7]

[edit] Mimas

Mimas is mostly made of water ice with a small amount of rock.^[8] It has a large crater for its size called Herschel. It is 130 km across, making it about a third as big as Mimas.^[9] The crater makes Mimas look like the Death Star from the Star Wars movies.

[edit] Enceladus

Enceladus is made of ice. It is denser than other icy moons. That suggests it also has some rock inside.^[10] It has smooth areas, cracks and some craters. The smooth areas are younger. Craters there have been erased within the past 100 million years. Water vapor was found over a smooth area around the south pole. The cracks and grooves suggest tectonics similar to Ganymede's. Some ridges similar to Europa's ridges were also found. Those suggest oceans like Europa's under some areas of Enceladus.^[11]Tidal forces from Dione could be powering some of this activity. It is because Enceladus orbits Saturn twice for every orbit by Dione. This makes Dione and Saturn tug on Enceladus. This is similar to how Europa and Ganymede's tidal forces on Io power Io's volcanoes.^[12]

[edit] Tethys

Tethys is an icy moon that has many craters, including the huge Odysseus. It is 400 km across, 1/5th as big as Tethys is. The crater had become flattened because the icy material does not hold its shape as well as rock would. There is also a large valley called Ithaca Chasma. It is 3 to 5 km deep, 100 km wide and 2000 km long, three fourth of the way around Tethys.^[13]

There are two moons, Telesto and Calypso, which share Tethys' orbit. Telesto is ahead of Tethys and Calypso is behind it.^[14]

[edit] Dione

Dione is made of lots of ice and maybe some rock in the core. It has lots of craters. The craters are flattened because the ice does not hold their shape as well as rock. One side has bright white lines that are fractures. Two moons share Dione's orbit. Helene is ahead of Dione and Polydeuces is behind it.^[15]

[edit] Rhea

Rhea is an icy moon similar to Dione with some rock in the core. It has many craters mostly on one side, and the other side has some bright white icy areas.^[16]

[edit] Titan

Titan is the largest moon of Saturn and the second largest one in the solar system.^[17] It is the only moon in the Solar System that has a thick atmosphere. The atmosphere is made of nitrogen, argon, methane and various organic compounds.^[18] Its surface has light and dark areas and few craters. However, the Cassini probe discovered a huge crater 440 km wide.^[19]

[edit] Hyperion

Hyperion is made of water ice with a little rock. It is potato shaped. It wobbles instead of rotating in the same way other moons do.^[20]

[edit] Iapetus

Iapetus is almost entirely ice.^[21] It has a light area called Roncevaux Terra that has craters.^[22] There is a big dark area called Cassini Regio that covers half of Iapetus. The dark material may be from Phoebe. Some of it is on the bottom of craters. Some huge craters and a ridge had been discovered in Cassini Regio by the Cassini probe. The ridge stretches 1300 km along the equator. It is up to 20 km high, which is over 2.26 times higher than Mount Everest.^[23] More huge craters were found in Roncevaux Terra when Cassini went by Iapetus again.^[24]

[edit] Phoebe

Phoebe is made of ice and rock. It looks dark because it has a layer of dark material on the outside. It also looks rough.^[25]

[edit] Other moons

There are two groups of small outer moons. Phoebe is part of the second outermost group.^[26]

[edit] How long is a day on this planet?

One day on Saturn is about 10 hours and 39 minutes in Earth time.^[27]

[edit] How long is a year on this planet?

One year on Saturn is about 29.46 Earth years long. That is 10,760 Earth days!^[28]

[edit] What is it made of?

Saturn has a rocky core. Around the core, there is ice. Above the ice is liquid metallic hydrogen. On top of that is gaseous hydrogen. There is no place where the hydrogen suddenly turns from a gas to a liquid.

The gaseous hydrogen makes up most of Saturn's atmosphere. Other gases there include helium and some other gases. There may be rain made of helium falling through the hydrogen. There is also ammonia on the surface.^[29]

[edit] How much would Saturn's gravity pull on me?

If you were floating close to the cloud tops of Saturn, it would pull you down with a force only a little stronger than the force of Earth's gravity.^[30] The effects of Saturn's large radius and its mass almost cancel each other out, making the force only a little bigger. So, if you weighed 100 lbs. on Earth, you would weigh 106 lbs. on Saturn.

[edit] Who is it named after?

Saturn is named after the Roman god of agriculture. He taught people how to farm. He was the father of Jupiter. Saturday is named after him.^[31]

[edit] References

1. ↑ http://www.nineplanets.org/saturn.html; http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
2. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=OverviewLong
3. ↑ http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=166
4. ↑ http://www.nineplanets.org/saturn.html; http://www.solarviews.com/eng/saturnrings.htm; http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings
5. ↑ http://www.nineplanets.org/saturn.html
6. ↑ http://www.factmonster.com/ce6/sci/A0860937.html
7. ↑ http://saturn.jpl.nasa.gov/faq/saturn.cfm#q13
8. ↑ http://www.nineplanets.org/mimas.html
9. ↑ http://www.nineplanets.org/mimas.html
10. ↑ http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20050830_CHARM_Esposito.pdf; http://www.ifa.hawaii.edu/faculty/jewitt/kb/phoebe.html
11. ↑ http://www.nineplanets.org/enceladus.html; http://www.nasa.gov/home/hqnews/2005/jul/HQ_05208_cassini_watery_world.html;
12. ↑ http://www.bbc.co.uk/science/space/solarsystem/saturn/enceladus.shtml; http://www.spacedaily.com/news/cassini-01e3.html
13. ↑ http://www.nineplanets.org/tethys.html
14. ↑ http://apod.gsfc.nasa.gov/apod/ap020519.html
15. ↑ http://www.nineplanets.org/dione.html; http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dione; http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Polydeuces
16. ↑ http://www.nineplanets.org/rhea.html; http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Rhea
17. ↑ http://www.nineplanets.org/titan.html; http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Titan
18. ↑ http://www.nineplanets.org/titan.html; http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Titan
19. ↑ http://www.nineplanets.org/titan.html; http://www.nasa.gov/mission_pages/cassini/media/cassini-021605.html
20. ↑ http://www.nineplanets.org/hyperion.html
21. ↑ http://www.nineplanets.org/iapetus.html
22. ↑ http://www.seasky.org/solarsystem/sky3g8.html
23. ↑ http://www.solarviews.com/cap/pia/PIA06166.htm; http://www.solarviews.com/eng/iapetus.htm; http://www.nineplanets.org/iapetus.html; http://antwrp.gsfc.nasa.gov/apod/ap030831.html
24. ↑ http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2763
25. ↑ http://www.solarviews.com/eng/phoebe.htm
26. ↑ http://www.factmonster.com/ce6/sci/A0860937.html
27. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Facts&System=Metric
28. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
29. ↑ http://www.nineplanets.org/saturn.html; http://www.solarviews.com/eng/saturn.htm; http://www.seasky.org/solarsystem/sky3g1.html
30. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
31. ↑ http://www.pantheon.org/articles/s/saturn.html; http://coolcosmos.ipac.caltech.edu/cosmic_kids/AskKids/saturn_name.shtml

[edit] Uranus

Uranus, the seventh planet from the Sun, was discovered by William Herschel on March 13, 1781.^[1]

Template:Robert Horning/Coolfacts

[edit] How big is Uranus?

Uranus is 51,118 kilometers or about four Earths wide. It is the third widest and fourth heaviest planet in the Solar System.

[edit] What is the surface of Uranus like?

Uranus does not have a surface that you could stand on without going deep into the atmosphere. Under the atmosphere, there may be an even mixture of rock and ice.^[2]

[edit] What are the rings around Uranus like?

Uranus has eleven rings. They are dark in colour and very hard to see. They were discovered by accident in 1977. Scientists were studying a bright star near Uranus. However, the star's light was blocked before and after it disappeared behind Uranus. From this, they figured out that Uranus has a ring system.^[3]

[edit] What are its moons like?

Uranus has 27 known moons, which places it third in the Solar System for number of moons! The five main ones are Miranda, Ariel, Umbriel, Titania and Oberon.^[4]

[edit] Miranda

Miranda is the smallest and closest of Uranus's major moons. It is mainly made of ice and rock. Miranda's surface has grooves, cliffs, and valleys. The moon was named after a character in The Tempest, a play by Shakespeare.^[5]

[edit] Ariel

Ariel is made of rock and ice. Ariel has many valleys, but not many craters. Ariel was named after a character in the poem The Rape of the Lock by Alexander Pope. Ariel is also a spirit in The Tempest by Shakespeare.^[6]

[edit] Umbriel

Umbriel is made of lots of ices and some rock. It is also the darkest of Uranus's major moons. Umbriel was named after a character in the poem The Rape of the Lock by Alexander Pope.^[7]

[edit] Titania

Titania is the largest moon of Uranus. It is mostly ice and rock. The surface is covered with canyons. It was named after the Queen of the Fairies in A Midsummer's Night Dream, a play by Shakespeare.^[8]

Template:Robert Horning

[edit] Oberon

Oberon is the outermost of the major moons of Uranus. It is made of the same things as Titania. It has many craters. Some of them have white rays around them and dark crater floors. It was named after the King of the Fairies in A Midsummer's Night Dream.^[9]

[edit] Other Moons

There are 13 tiny moons known to be orbiting Uranus inside Miranda's orbit. Nine more tiny moons are known to be in big orbits beyond Oberon's orbit.^[10]

[edit] How long is a day on Uranus?

One day on Uranus is about 27 Earth hours long. Uranus spins on its side, maybe because of a big impact early in the history of the Solar System.^[11]

[edit] How long is a year on Uranus?

One year on Uranus would be 30,708 days or 84 years on Earth.^[12]

[edit] What is Uranus made of?

Unlike Jupiter and Saturn, Uranus is thought to be made mostly of rock and ice. The gases in its atmosphere are mostly hydrogen and helium. Other gases found in smaller amounts are ammonia, water, and methane.^[13] Uranus' blue color comes from methane clouds, which absorb red light and reflect blue light.^[14]

[edit] How much would Uranus's gravity pull on me?

If you were floating close to the cloud tops of Uranus, you would be pulled down with a force about 86% of Earth's gravity.^[15]

[edit] Who is Uranus named after?

Uranus was named after Ouranos, the Greek name for the sky. According to Greek mythology, Ouranos was the husband and son of Gaia, Mother Earth.^[16]

Next Topic: Neptune

[edit] References

1. ↑ http://www.nineplanets.org/uranus.html
2. ↑ http://www.solarviews.com/eng/uranus.htm; http://www.nineplanets.org/uranus.html
3. ↑ http://www.solarsystem.org.uk/uranus/
4. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/index.html; http://www.nineplanets.org/uranus.html
5. ↑ http://www.nineplanets.org/miranda.html; http://www.bbc.co.uk/science/space/solarsystem/uranus/miranda.shtml
6. ↑ http://www.nineplanets.org/ariel.html; http://www.bbc.co.uk/science/space/solarsystem/uranus/ariel.shtml
7. ↑ http://www.nineplanets.org/umbriel.html; http://www.bbc.co.uk/science/space/solarsystem/uranus/umbriel.shtml
8. ↑ http://www.nineplanets.org/titania.html; http://www.bbc.co.uk/science/space/solarsystem/uranus/titania.shtml
9. ↑ http://www.nineplanets.org/oberon.html; http://www.bbc.co.uk/science/space/solarsystem/uranus/oberon.shtml
10. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html
11. ↑ Gierasch, Peter J., and Philip D. Nicholson. "Uranus." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar577720; http://www.nasa.gov/worldbook/uranus_worldbook.html
12. ↑ Gierasch, Peter J., and Philip D. Nicholson. "Uranus." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar577720; http://www.nasa.gov/worldbook/uranus_worldbook.html
13. ↑ http://www.nineplanets.org/uranus.html; http://www.solarviews.com/eng/uranus.htm
14. ↑ http://www.solarviews.com/eng/uranus.htm
15. ↑ Gierasch, Peter J., and Philip D. Nicholson. "Uranus." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar577720; http://www.nasa.gov/worldbook/uranus_worldbook.html
16. ↑ http://www.nineplanets.org/uranus.html

[edit] Neptune

Template:Robert Horning/Coolfacts

[edit] How big is this planet ?

Template:Robert Horning

Neptune is very similar to Uranus in size. Its diameter is only slightly smaller, at 49,528 km wide. ^[1] It is almost as big as four Earths in length.^[2]

[edit] What is its surface like?

The atmosphere of Neptune has some dark blue spots. When the Voyager probe went by Neptune in 1989, it saw a large one called the Great Dark Spot. In 1994, it vanished, but later reappeared.^[3] There is also a large white cloud nicknamed "Scooter." It goes around Neptune every 16 hours.^[4] The winds of Neptune are very fast, blowing at up to 2000 km per hour(the fastest in the entire solar system).^[5] That is about four times faster than the fastest recorded tornado on Earth.

[edit] What are its rings like?

Neptune has some faint rings that are dark and hard to see. There are clumps in some parts of the rings where the material is denser.^[6]

[edit] What are its moons like?

Neptune has 13 moons. There could be more.^[7]

[edit] Inner Moons

There are five small potato-shaped moons orbiting close to Neptune.

[edit] Proteus

Proteus is a dark moon about 418 km across. It has an irregular shape. In Roman mythology Proteus was a sea-god who could change into any shape he wanted.^[8]

[edit] Triton

Triton is the largest moon of Neptune. Scientists think that it is a lot like Pluto. It is 2700 km across. It is made of rock and ice. It has a surface temperature of −235 °C Triton has a very thin atmosphere made up of nitrogen and a little methane.

There are volcanoes that have eruptions of liquid nitrogen, dust or methane compounds. The eruptions happen because of the seasons. There are few craters because the eruptions cover them up. There are ice caps that change sizes with the seasons. There are also ridges and valleys. They may have formed because of repeated freezing and thawing.

An interesting thing about Triton's orbit is that it goes around Neptune in the opposite direction that Neptune's rotates. Because of this, scientists think that Triton was captured by Neptune long ago. In Roman mythology, Triton was the son of Neptune.^[9]

[edit] Nereid

Nereid is an irregularly shaped moon about 340 km across. Its orbit is very eccentric or noncircular. It may have been captured by Neptune or moved into the eccentric orbit by Triton's gravity when Triton got captured. In Roman mythology Nereids were sea nymphs.^[10]

[edit] Outer Moons

There are five other known moons. They are small potato-shaped moons far from Neptune. There might be more we haven't seen yet.

[edit] How long is a day on this planet?

A day on Neptune lasts 16 hours and 7 minutes.^[11]

[edit] How long is a year on this planet?

One year on Neptune is about 165 Earth years, or 60,265 days.^[12]

[edit] What is it made of?

Neptune is made of rock and metal in the core. The core is probably bigger than Uranus's because Neptune weighs more, but is the same size. Around the core is rock, water, ammonia and methane. The atmosphere is made of hydrogen and helium. Lower down in the atmosphere, there is methane and ammonia too. The methane makes Neptune look blue-green.^[13]

[edit] How much would Neptune's gravity pull on me?

If you were floating close to the cloud tops of Neptune, it would pull you down with a force only a little stronger than the force of Earth's gravity.^[14] The effects of Neptune's larger radius and its mass almost cancel out, making the force only a little bigger.

[edit] Who is it named after?

Neptune is named after the Roman god of the seas, also known as Poseidon in ancient Greece. ^[15]

Next Topic: Pluto

[edit] References

1. ↑ Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar386900; http://www.nasa.gov/worldbook/neptune_worldbook.html
2. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html
3. ↑ Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar386900; http://www.nasa.gov/worldbook/neptune_worldbook.html
4. ↑ http://www.nineplanets.org/neptune.html; http://www.moreheadplanetarium.org/index.cfm?fuseaction=page&filename=science_resources_neptune.html
5. ↑ http://www.nineplanets.org/neptune.html; http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level1/neptune.html
6. ↑ Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar386900; http://www.nasa.gov/worldbook/neptune_worldbook.html
7. ↑ http://www.nineplanets.org/neptune.html
8. ↑ http://www.nineplanets.org/proteus.html
9. ↑ http://www.nineplanets.org/triton.html
10. ↑ http://www.nineplanets.org/nereid.html
11. ↑ Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar386900; http://www.nasa.gov/worldbook/neptune_worldbook.html
12. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html; Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar386900; http://www.nasa.gov/worldbook/neptune_worldbook.html
13. ↑ http://www.nineplanets.org/neptune.html; Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar386900; http://www.nasa.gov/worldbook/neptune_worldbook.html
14. ↑ Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 281. West Publishing Company. ISBN 0-314-64212-9
15. ↑ Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 282. West Publishing Company. ISBN 0-314-64212-9

[edit] Pluto

Pluto is a dwarf planet that was discovered by the astronomer Clyde W. Tombaugh in Arizona on February 18, 1930.^[1]

[edit] How big is Pluto?

Pluto's mass is about 12,500,000,000,000,000,000,000 kilograms.^[2] While this may seem large, it's only about 1/500th of the Earth's mass. Pluto is between 2200 and 2400 kilometers across.^[3] Its surface area is about 17,950,000 square kilometers (or 1/30th of the Earth's).^[4] Its volume is 7,150,000,000 km³ (or 1/150th of the Earth's).^[5]
Template:Robert Horning

[edit] What is its Surface like?

We don't really know for sure what its surface is like. No spacecraft has ever been there, and even the best telescopes can't see any detail. It is certainly very cold, at about -230 °C.^[6] The surface is covered with ice.^[7] Pluto also has a very thin atmosphere which freezes when Pluto moves far away from the Sun.^[8]

The image to the left shows Pluto's color.

[edit] What are Pluto's moons like?

Pluto has three known moons. The largest is called Charon. Charon is about half as wide as Pluto. Because Pluto and Charon are so close in size, they are sometimes called a "double planet".^[9] Charon's surface is covered in water ice.^[10] In Roman mythology, Charon took dead souls across the river Acheron to the land of the dead.^[11] Two other moons were discovered in 2005. They have been named Nix and Hydra.^[12]

[edit] How long is a day on Pluto?

One day on Pluto is about 6.487 Earth days long. Like Uranus, Pluto also spins on its side.^[13]

[edit] How long is a year on Pluto?

One year on Pluto would be about 90,613 days or 248 years on Earth!^[14]

[edit] What is it made of?

Scientists believe Pluto is made mostly of rock and ice,^[15] but they will not be sure until more research is done. The discovery of Charon helped scientists estimate the density of Pluto. The information collected told them what Pluto was and was not made out of. If Pluto were made out of heavy solids, it would have a very high density. If it were made of gases, it would have a low density. Pluto is somewhere in between, so it is probably made of rock and ice.

[edit] How much would Pluto's gravity pull on me?

If you were on Pluto, gravity would be only 0.06 times as strong as it is on Earth. ^[16] This means you could do really high jumps—even more than people could on the Moon!

[edit] Who is Pluto named after?

Pluto was named after the Roman god of the underworld. In Roman mythology, he kidnapped Proserpina (Persephone) so he could marry her. This made her mother, the goddess of agriculture, very sad, causing winter. To end winter, Jupiter, his brother, sent Mercury to get her back. Pluto agreed that she could go back, assuming she had not eaten anything from the underworld. However, she had eaten six pomegranate seeds, so Jupiter decided she had to spend six months in the underworld each year. This is the Roman myth of winter. When she goes to the underworld, everything stops growing. When she comes back, her mother is happy again, and life returns. ^[17]

[edit] Is Pluto a planet?

Pluto has been officially classified as a dwarf planet, which is different than a regular planet. One of the reasons is that it is a lot smaller than other planets - although it is the tenth largest known object that revolves around the sun, it is smaller than many moons, including Earth's moon. Scientists used to think that Pluto was a lot larger than it actually is,^[18] and it was thought of as the ninth planet for many years.

Another key reason is that Pluto is part of a large group of objects called the Kuiper Belt, which all revolve around the Sun in the area beyond Neptune. It appears that there are several Pluto-sized objects in this part of the solar system, as well as millions of smaller objects.

In the world of astronomy, not everyone agrees.^[19] However, most scientists now accept that Pluto isn't a regular planet.

Next Topic: Comets

[edit] References

1. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html
2. ↑ Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 285. West Publishing Company. ISBN 0-314-64212-9; http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html
3. ↑ Spinrad, Hyron. 2004 "Pluto." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar435500; http://www.nasa.gov/worldbook/pluto_worldbook.html; Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 285. West Publishing Company. ISBN 0-314-64212-9; http://amazing-space.stsci.edu/resources/fastfacts/pluto.php.p=Astronomy+basics@,eds,astronomy-basics.php&a=,eds
4. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html
5. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html
6. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html; Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 285. West Publishing Company. ISBN 0-314-64212-9; http://www.nasa.gov/worldbook/pluto_worldbook.html
7. ↑ Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 287. West Publishing Company. ISBN 0-314-64212-9; http://www.nasa.gov/worldbook/pluto_worldbook.html
8. ↑ Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 287. West Publishing Company. ISBN 0-314-64212-9; http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html
9. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Plu_Charon
10. ↑ http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html
11. ↑ http://www.pantheon.org/articles/c/charon.html
12. ↑ http://www.space.com/scienceastronomy/060621_nix_hydra.html
13. ↑ http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html; http://www.nineplanets.org/pluto.html
14. ↑ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Pluto&Display=Overview
15. ↑ http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html
16. ↑ Snow, Theodore P. (1996) "The Outer Planets." In The Dynamic Universe: An Introduction to Astronomy. pp. 285. West Publishing Company. ISBN 0-314-64212-9; http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html
17. ↑ http://www.windows.ucar.edu/tour/link=/mythology/persephone_seasons.html; http://www.pantheon.org/articles/p/persephone.html
18. ↑ Sobel, Dava (2005) "The Planets." pp. 220. Harper Perennial Publishing Company. ISBN 1-84115-621-3
19. ↑ Spinrad, Hyron. 2004 "Pluto." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar435500; http://www.nasa.gov/worldbook/pluto_worldbook.html