• 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—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.
     
    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.
    meteoroid
    This isn't a potato—technically, it's not a meteoroid, either—it's an asteroid named Eros.
    Meteoroids Mar Missions
    Meteoroids can damage satellites streaking through space as well as those in orbit. In 1967, the Mariner IV spacecraft encountered a meteoroid stream on its journey to Mars. The meteoroids damaged some of Mariner IV’s thermal insulation, although the mission continued successfully. In 1993, the European communications satellite Olympus was hit by a meteoroid associated with the Perseid meteor shower. The Perseid hit Olympus’ electronics bay, destroying the device (control movement gyroscope) that controlled the spacecraft’s momentum. By the time engineers were able to get the tumbling spacecraft under control, its fuel was exhausted and the mission had to be scrapped.
  • Term Part of Speech Definition Encyclopedic Entry
    associate Verb

    to connect.
    asteroid Noun

    irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.
    asteroid belt Noun

    area of the solar system between the orbits of Mars and Jupiter filled with asteroids.
    astronaut Noun

    person who takes part in space flights.
    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    		 Encyclopedic Entry: atmosphere
    avoid Verb

    to stay away from something.
    bolide Noun

    unusually large, bright meteor.
    catastrophic Adjective

    very bad.
    celestial body Noun

    natural object in space, such as a planet or star. Also called an astronomical object.
    collision Noun

    crash.
    comet Noun

    celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.
    crater Noun

    bowl-shaped depression formed by a volcanic eruption or impact of a meteorite.

    		 Encyclopedic Entry: crater
    crop Noun

    agricultural produce.

    		 Encyclopedic Entry: crop
    damage Noun

    harm that reduces usefulness or value.
    debris Noun

    remains of something broken or destroyed; waste, or garbage.
    dense Adjective

    having parts or molecules that are packed closely together.
    dinosaur Noun

    very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago.
    disintegrate Verb

    to fall apart and disappear.
    dust Noun

    microscopic particles of rocks or minerals drifting in space. Also called cosmic dust or space dust.
    endanger Verb

    to put at risk.
    engineer Noun

    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 Noun

    process of complete disappearance of a species from Earth.
    fragile Noun

    delicate or easily broken.
    gas Noun

    state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.
    gas giant Noun

    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.
    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    		 Encyclopedic Entry: habitat
    impact Noun

    collision or crash.
    inner planet Noun

    one of the four rocky planets closes to the sun: Mercury, Venus, Earth, or Mars. Also called a terrestrial planet.
    instrument Noun

    tool.
    iron Noun

    chemical element with the symbol Fe.
    Kuiper belt Noun

    region in the outer solar system containing thousands of tiny, icy bodies and thought to be the source of short-period comets (comets that take less than 200 years to to orbit the sun).
    lunar Adjective

    having to do with Earth's moon or the moons of other planets.
    maneuver Noun

    a skillful movement.
    massive Adjective

    very large or heavy.
    mechanism Noun

    process or assembly that performs a function.
    metal Noun

    category of elements that are usually solid and shiny at room temperature.
    meteor Noun

    rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.

    		 Encyclopedic Entry: meteor
    meteorite Noun

    type of rock that has crashed into Earth from outside the atmosphere.

    		 Encyclopedic Entry: meteorite
    meteoroid Noun

    small, rocky body traveling around the sun.

    		 Encyclopedic Entry: meteoroid
    meteor shower Noun

    large amount of rocky debris falling into Earth's atmosphere, usually when Earth passes through the orbit of a comet.
    microscope Noun

    instrument used to view very small objects by making them appear larger.
    mineral Noun

    inorganic material that has a characteristic chemical composition and specific crystal structure.
    monitor Verb

    to observe and record behavior or data.
    Moon Noun

    Earth's only natural satellite.
    NASA Noun

    (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 hazard Noun

    event in the physical environment that is destructive to human activity.
    nucleus Noun

    head of a comet, mostly composed of frozen gases and solid particles of ice.
    Oort cloud Noun

    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 Noun

    path of one object around a more massive object.
    outer planet Noun

    any one of the four gas giants that orbit the sun beyond the asteroid belt: Jupiter, Saturn, Neptune, or Uranus.
    particle Noun

    small piece of material.
    planet Noun

    large, spherical celestial body that regularly rotates around a star.

    		 Encyclopedic Entry: planet
    potential Adjective

    possible.
    pressurize Verb

    to adjust and maintain the atmospheric pressure in a contained area.
    process Noun

    continuous action, operation, or series of changes taking place in a defined manner.
    protect Verb

    to take action to prevent injury or attack.
    region Noun

    any area on Earth with one or more common characteristics. Regions are the basic units of geography.

    		 Encyclopedic Entry: region
    resistance Noun

    the act of opposing something.
    rock Noun

    natural substance composed of solid mineral matter.
    shed Verb

    to release or cast off.
    shielding Noun

    protective material or device.
    shock wave Noun

    moving, measurable change in pressure and density of a material.
    silicate Noun

    most common group of minerals, all of which include the elements silicon (Si) and oxygen (O).
    solar system Noun

    the sun and the planets, asteroids, comets, and other bodies that orbit around it.
    spacecraft Noun

    vehicle designed for travel outside Earth's atmosphere.
    space weathering Noun processes that act on any celestial body exposed to outer space, such as exposure to the solar wind and asteroid impacts.
    sporadic Adjective

    occasional and happening in isolated instances.
    sun Noun

    star at the center of our solar system.
    tail Noun

    stream of gas or dust debris behind a comet.
    thermal Adjective

    having to do with heat or temperature.
    travel Noun

    movement from one place to another.
    valuable Adjective

    worth a considerable amount of money or esteem.
    vehicle Noun

    device used for transportation.
    vulnerable Adjective

    capable of being hurt.
    withstand Verb

    to stand up to or endure.

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Editor

Jeannie Evers, Emdash Editing

Producer

Caryl-Sue, National Geographic Society

Last Updated

Aug. 4, 2014

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