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Our Solar System

Science, Grade 7

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Formation of Our Solar System Solar systems begin in the dust and gas clouds found in between the stars. The dust is composed of elements like iron and carbon. The gas clouds are composed of hydrogen and helium. These dusty clouds are called nebulae. Through a process, called “accretion,” dust particles formed larger bodies that eventually became planetesimals. Close to the Sun, the rocky planetesimals grew by accretion to become the rocky planets. In the outer reaches of the solar system, the gases like hydrogen and helium accreted to rocky cores forming planets called gas giants. The Sun The Sun is a burning ball of gas (mostly hydrogen and helium) that is held together by gravity. The Sun’s energy is produced by nuclear fusion reactions. The Inner Planets The inner planets are also known as the terrestrial planets or as rocky planets. The terrestrial planets are Mercury, Venus, Earth and Mars. Mercury is the smallest of the terrestrial planets. Mercury has no atmosphere and no moon. Venus is referred to as “Earth’s twin ” or “sister planet” because it has similar composition, gravity, and size to Earth. It has the densest atmosphere of the terrestrial planets consisting of carbon dioxide and clouds of sulfuric acid. Earth is the third planet from the Sun and the fifth largest. Approximately 70% of the Earth's surface is covered with water. The Earth's atmosphere is approximately 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water. Mars has had a very active volcanic history. There is growing evidence that there were large amounts of water on Mars at one time. Jupiter is the largest planet in our solar system. It likely has a rocky core, but Jupiter is mostly made up of hydrogen and helium. Saturn is the second largest planet in the solar system. Scientists believe that it actually creates more heat itself than it receives from the Sun. It is composed mainly of hydrogen and helium. Uranus is visible to the naked eye, but due to its distance from the Earth it was not recognized as a planet until 1781. It was the first planet to be discovered with the use of a telescope. The gas giant furthest from the Sun is Neptune. It has a rock and ice core surrounded by a large layer of ice and a layer of hydrogen and helium gas. The highest wind speeds in the solar system are on Neptune. The Outer Planets These four outer planets - Jupiter, Saturn, Uranus, and Neptune - are also referred to as the gas giants or Jovian planets. Pluto Until 2006, Pluto was considered the 9th planet from the Sun. Recently astronomers have concluded that Pluto is not a planet by the strict definition of a planet. It is therefore no longer listed as a planet but as a dwarf planet in a region of the solar system called the Kuiper Belt. Images courtesy of NASA. © Copyright NewPath Learning. All Rights Reserved. 94-4110 www.newpathlearning.com Our Solar System

Formation of Our Solar System How do solar systems form? _____________________________________________ _____________________________________________________________________ Describe: Rocky planets: ________________________________________________________ ____________________________________________________________________ Gas giants: ___________________________________________________________ ________________________________________________ The Sun How is the Sun’s energy produced? ______________________________________________ ______________________________________________ ______________________________________________ The Inner Planets The inner planets are also known as the ____________________ ____________________or as ____________________ ____________________ . The terrestrial planets are ____________________, ____________________, ____________________ and ____________________ . Describe: Mercury: ___________________________________ ____________________________________________ ____________________________________________ Venus: _____________________________________ ____________________________________________ ____________________________________________ Earth: ______________________________________ ____________________________________________ ____________________________________________ Mars: _______________________________________ ____________________________________________ ____________________________________________ The Outer Planets These four outer planets - ____________________ , ____________________ , ____________________ , and ____________________ - are also referred to as the ____________________ ____________________ or ____________________ ____________________ . Describe: Jupiter: _________________________________ _______________________________________ _______________________________________ Saturn: ________________________________ _____________________________________ _____________________________________ _____________________________________ Uranus: ___________________________________ __________________________________________ __________________________________________ Neptune: __________________________________ ___________________________________________ ___________________________________________ Pluto: ______________________________________ ____________________________________________ ____________________________________________ Key Vocabulary Terms • accretion • Earth • gas giants • inner planets • Jovian planets • Jupiter • Mars • Mercury • nebulae • Neptune • outer planets • planetesimals • rocky planets • Saturn • terrestrial planets • Uranus • Venus © Copyright NewPath Learning. All Rights Reserved. 94-4110 www.newpathlearning.com Our Solar System \|xiBAHBDy01791sz\

Our Solar System

Science, Grade 7

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