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Section 13.15: Other Objects in the Solar System Planetary Moons Moons (also known as satellites) are large natural objects that revolve around planets. Several planets have more than one moon. The most famous satellite of any planet is Earth’s Moon. Information about the Moon: • • • • • • • • The moon orbits the Earth The moon is the only natural satellite of the Earth The moon completes one rotation after 27 and a third days. The distance between the Earth and the Moon is 384,385 km. The weight of the moon is 1/81 that of the Earth The diameter is ¼ of the Earth's. (3479 km) The moon has no atmosphere Surface is filled with hills and valleys as well as craters (caused by impact of objects from space) • There have been 6 visits to the moon (between 1969 and 1972) Asteroid: Small rocky objects found in an asteroid belt around the Sun between the orbits of Mars and Jupiter. (There is a large gap between the orbits of Mars and Jupiter) Scientists believe that the asteroids might have formed into a planet if Jupiter’s gravitational pull hadn’t been so strong. Could we someday mine the minerals on asteroids?!? Their gravity would allow spacecraft carrying minerals to blast off more easily. Meteoroid: A lump of rock or metal that is trapped by Earth’s gravity and pulled down through the Earth’s atmosphere. Meteor: A bright streak of light across the sky, caused by a burning meteoroid. Meteoroids burn when they rub against molecules in the air causing friction. “Falling Stars” are actually Meteors. The 3 most active Meteor Showers are: Perseid (August 12), Geminid (December 14) and Quadrantid (January 3 or 4) Meteorite: A meteor that hits the Earth’s surface (creating a crater) before it completely burns up in the Earth’s atmosphere. Comet: A chunk of ice and dust that travels in a larger orbit around the Sun. As the comet approaches the sun, the solar radiation causes the frozen substances to become gases. The solar wind pushes these gases outward, forming a tail that can be millions of kilometers long. Many comets have regular periods of revolution. (ex. Halley’s Comet has a period of 76 years)