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Meteoroids are lumps of rock or iron that orbit the sun, just as planets, asteroids, and comets do. Meteoroids, especially the tiny particles called micrometeoroids, 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 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 (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.
Other 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 micrometeoroids. 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. Meteoroids 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 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 to 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 Earth's surface 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, likely led to the extinction of the dinosaurs and almost every other form of life on Earth.
This isn't a potato—technically, it's not a meteoroid, either—it's an asteroid named Eros.
Photograph courtesy NASA/JHUAPL
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.
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.
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.
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.
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.
Noun
environment where an organism lives throughout the year or for shorter periods of time.
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.
Noun
rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.
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.
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.
Noun
any area on Earth with one or more common characteristics. Regions are the basic units of geography.
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.
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.
