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1 Your web browser (Safari 7) is out of date. For more security, comfort and the best experience on this site: Update your browser Ignore METEO RO ID For the complete encyclopedic entry with media resources, visit: Meteoroids are lumps of rock or iron that orbit the sun, just as planets, asteroids, and comets do. Meteoroids, especially the tiny particles called micrometeroids, are extremely common throughout the solar system. They orbit the sun among the rocky inner planets, as well as the gas giants that make up the outer planets. Meteoroids are even found on the very edge of the solar system, in regions called the Kuiper belt and the Oort cloud. Different meteoroids travel around the sun at different speeds and in different orbits. The fastest meteoroids travel through the solar system at a speed of around 42 kilometers per second (26 miles per second). Many meteoroids are formed from the collision of asteroids, which orbit the Sun between the paths of Mars and Jupiter in a region called the asteroid belt. As asteroids smash into each other, they produce crumbly debris meteoroids. The force of the asteroid collision can throw the meteoroid debris and sometimes the asteroids themselves out of their regular orbit. This can put the meteoroids on a collision course with a planet or moon. Others meteoroids are the debris that comets shed as they travel through space. As a comet approaches the sun, the dirty snowball of the comet s nucleus sheds gas and dust. The dusty tail may contain hundreds or even thousands of meteoroids and micrometeroids. Meteoroids shed by a comet usually orbit together in a formation called a meteoroid stream. A very small percentage of meteoroids are rocky pieces that break off from the Moon and Mars after celestial bodies often asteroids or other meteoroids 1 of 8

2 impact their surfaces. Meteoroid impacts are probably the largest contributor to space weathering. Space weathering describes the processes that act upon a celestial body that doesn t have an airy atmosphere, such as asteroids, many moons, or the planets Mars and Mercury. Meteroroids crash into these bodies, creating craters and throwing space dust (more meteoroids) back into the solar system. Most meteoroids are made of silicon and oxygen (minerals called silicates) and heavier metals like nickel and iron. Iron and nickel-iron meteoroids are very massive and dense, while stony meteoroids are lighter and more fragile. Assessing the Impact Meteoroids are generally as harmless as any other celestial body they re specks of dust floating around the sun. Space agencies such as NASA do monitor the movement of meteoroids, however, for two reasons: potential impact with spacecraft and potential impact with Earth. Spacecraft The impact of even a micrometeoroid can damage the windows, thermal protection systems, and pressurized containers of spacecraft. This could endanger astronauts, result in the loss of valuable scientific instruments, and cost millions of dollars. Engineers must prepare and equip spacecraft to avoid or withstand meteoroid impacts. To do this, they have classified three different meteoroid environments : the sporadic environment, the shower environment, and the lunar environment. The sporadic environment describes the threat of meteoroids created by asteroids or comets. Engineers must determine what area of the spacecraft is most vulnerable to sporadic meteoroids, and prepare stronger shielding mechanisms. 2 of 8

3 The shower environment describes the threat of meteoroid streams associated with comets passing through Earth s orbit. On Earth, these debris fields are associated with meteor showers. Engineers must be able to maneuver the spacecraft in order take its most vulnerable areas out of the path of the meteoroid stream. The lunar environment describes the threat of meteoroids to astronauts or facilities on the Moon. Although there have been no long-term astronaut stays on the moon, engineers have designed space suits, vehicles, and habitats that can withstand meteoroid impacts. Earth When a meteoroid passes through Earth s atmosphere, it heats up due to air resistance. The heat causes gases around the meteoroid to glow brightly. This glowing meteoroid is called a meteor, sometimes nicknamed a shooting star. Most meteoroids that enter Earth s atmosphere disintegrate before they reach the ground. The pieces that do strike the surface of the Earth are called meteorites. Both meteors and meteorites can become natural hazards to the communities they impact. Very large meteors called bolides may explode in the atmosphere with the force of 500 kilotons of TNT. These meteors and the shock waves they produce may cause burns and even death, as well as damage to buildings and crops. An actual impact where part of the space rock actually crashes into Earth can be even more catastrophic. A single impact event about 65 million years ago, for instance, led to the extinction of the dinosaurs and almost every other form of life on Earth. Vocabulary Term 3 of 8

4 Term associate verb to connect. asteroid asteroid belt irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter. area of the solar system between the orbits of Mars and Jupiter filled with asteroids. astronaut person who takes part in space flights. atmosphere layers of gases surrounding a planet or other celestial body. avoid verb to stay away from something. bolide unusually large, bright meteor. catastrophicadjectivevery bad. celestial body collision crash. comet crater natural object in space, such as a planet or star. Also called an astronomical object. celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris. bowl-shaped depression formed by a volcanic eruption or impact of a meteorite. crop agricultural produce. damage harm that reduces usefulness or value. debris dense dinosaur remains of something broken or destroyed; waste, or garbage. having parts or molecules that are packed closely adjective together. disintegrate verb dust very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago. to fall apart and disappear. microscopic particles of rocks or minerals drifting in space. Also called cosmic dust or space dust. 4 of 8

5 Term endanger verb to put at risk. engineer person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer). equip verb to prepare or provide the right equipment. extinction process of complete disappearance of a species from Earth. fragile delicate or easily broken. gas gas giant habitat state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion. one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. Also called a Jovian planet. environment where an organism lives throughout the year or for shorter periods of time. impact collision or crash. inner planet instrument tool. one of the four rocky planets closes to the sun: Mercury, Venus, Earth, or Mars. Also called a terrestrial planet. iron chemical element with the symbol Fe. Kuiper belt lunar region in the outer solar system containing thousands of tiny, icy bodies and thought to be the source of shortperiod comets (comets that take less than 200 years to to orbit the sun). having to do with Earth's moon or the moons of other adjective planets. maneuver a skillful movement. massive mechanism adjectivevery large or heavy. process or assembly that performs a function. 5 of 8

6 Term metal category of elements that are usually solid and shiny at room temperature. meteor rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star. meteorite type of rock that has crashed into Earth from outside the atmosphere. meteoroid small, rocky body traveling around the sun. large amount of rocky debris falling into Earth's meteor atmosphere, usually when Earth passes through the orbit shower of a comet. mineral inorganic material that has a characteristic chemical composition and specific crystal structure. monitor verb to observe and record behavior or data. Moon Earth's only natural satellite. NASA (National Aeronautics and Space Administration) the U.S. space agency, whose mission statement is "To reach for new heights and reveal the unknown so that what we do and learn will benefit all humankind." natural event in the physical environment that is destructive to hazard human activity. nucleus head of a comet, mostly composed of frozen gases and solid particles of ice. Oort cloud region on the edge of the solar system filled with millions of tiny comets, some of which are drawn into the inner solar system by passing stars. orbit path of one object around a more massive object. outer planet any one of the four gas giants that orbit the sun beyond the asteroid belt: Jupiter, Saturn, Neptune, or Uranus. particle small piece of material. 6 of 8

7 planet potential pressurize process large, spherical celestial body that regularly rotates around a star. adjectivepossible. verb to adjust and maintain the atmospheric pressure in a contained area. continuous action, operation, or series of changes taking place in a defined manner. protect verb to take action to prevent injury or attack. region any area on Earth with one or more common characteristics. Regions are the basic units of geography. resistance the act of opposing something. rock natural substance composed of solid mineral matter. shed verb to release or cast off. shielding protective material or device. shock wave silicate solar Term system moving, measurable change in pressure and density of a material. most common group of minerals, all of which include the elements silicon (Si) and oxygen (O). the sun and the planets, asteroids, comets, and other bodies that orbit around it. spacecraft vehicle designed for travel outside Earth's atmosphere. space weathering sporadic processes that act on any celestial body exposed to outer space, such as exposure to the solar wind and asteroid impacts. adjectiveoccasional and happening in isolated instances. sun star at the center of our solar system. tail stream of gas or dust debris behind a comet. thermal adjectivehaving to do with heat or temperature. 7 of 8

8 Term TNT (trinitrotoluene) chemical compound often used as a predictable, reliable explosive material with relatively safe handling properties. travel movement from one place to another. valuable adjectiveworth a considerable amount of money or esteem. vehicle device used for transportation. vulnerable adjectivecapable of being hurt. withstand verb to stand up to or endure. Websites NASA: Starchild Meteoroids NASA: Meteoroid Environment Office NASA: Solar System Exploration Meteors and Meteorites American Meteor Society National Geographic Society. All rights reserved. 8 of 8