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| The Sun | Mercury | Venus | Earth | Mars | |
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The
Sun The sun is the star at the center of our solar system. Over 99% of all the matter in our solar system is found in the sun. The sun produces energy by converting hydrogen into helium. The center of the sun, referred to as the core, contains about 700 million tons of hydrogen gas that is converted into 695 million tons of helium gas every second. This process, called nuclear fusion, produces enormous amounts of energy, but here on Earth we only receive one billionth of that total energy. Light from the sun travels at about 186 thousand miles per second. This means it takes just over 8 minutes for light from the sun to reach us on Earth. 
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Mercury Mercury is the closest planet to the sun. This planet is slightly larger than Earth’s moon and is the second smallest planet in our solar system, behind Pluto. Since Mercury is closest to the sun it has less distance to travel to completely orbit our star. One year on Mercury is equal to 88 days here on Earth. Mercury also experiences extremely hot and cold temperatures. An average day on Mercury records temperatures as high as 870° Fahrenheit (°F) and as cold as -300°F. Mercury has a thin atmosphere made of hydrogen and helium.
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Venus Venus is the second planet from the sun and is sometimes referred to as Earth’s sister planet because the two planets are similar in size. One year on Venus is equal to 225 Earth days. The temperature on the surface of Venus reaches a scorching 900°F. Venus has an extremely thick atmosphere made primarily of carbon dioxide with traces of nitrogen, carbon monoxide, argon, sulfur dioxide, and water vapor. This heavy atmosphere creates enormous surface pressure, about 90 times more pressure on the surface of Venus than here on Earth.
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Earth Earth is the third planet from the sun. Over 70% of Earth’s surface is covered with water, and 97% of that water is salty. The fresh water that we drink only makes up 3% of the Earth’s total water. One year on the Earth is 365 ¼ days. Every four years an extra day has accumulated and we have what is called a leap year with an extra day in February. Our atmosphere, made of mostly of nitrogen and oxygen, provides protection for all living things on Earth. Harmful ultraviolet rays from the sun are filtered out by our atmosphere’s ozone layer before they reach Earth’s surface. The average temperature on Earth is 45°F.
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Mars Mars is the fourth planet from the sun and is often referred to as the Red Planet. This reddish color comes from large amounts of rust in the planet’s soil. The surface of Mars is covered with narrow channels. This leads scientists to believe that water was once flowing on the martian surface. The surface temperature on Mars ranges from –190°F to 90°F. Mars has retained a thin atmosphere composed primarily of carbon dioxide.
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| All images courtesy of NASA/JPL-Caltech | Main | Inner Solar System | Outer Solar System |
| Questions? Contact
Kate Geissler at geisslkr@uwec.edu Page Last Updated 03/30/2004 |