A micrometeoroid is a tiny meteoroid
A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...

; a small particle of rock in space, usually weighing less than a gram
The gram is a metric system unit of mass....

. A micrometeor or micrometeorite is such a particle that enters the Earth's atmosphere or falls to Earth.

Scientific interest

Micrometeoroids are very small pieces of rock or metal broken off from larger chunks of rock and debris often dating back to the birth of the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. Micrometeoroids are extremely common in space. Tiny particles are a major contributor to space weathering
Space weathering
Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment. Airless bodies incur many weathering processes:* collisions of galactic cosmic rays and solar cosmic rays,* irradiation, implantation, and sputtering from solar wind...

 processes. When they hit the surface of the Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, or any airless body (Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

, the asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s, etc.), the resulting melting and vaporization causes darkening and other optical changes in the regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...

. In order to understand the micrometeoroid population better, a number of spacecraft (including Lunar Orbiter 1
Lunar Orbiter 1
The Lunar Orbiter 1 robotic spacecraft, part of the Lunar Orbiter Program, was designed primarily to photograph smooth areas of the lunar surface for selection and verification of safe landing sites for the Surveyor and Apollo missions...

, Luna 3
Luna 3
The Soviet space probe Luna 3 of 1959 was the third space probe to be sent to the neighborhood of the Moon, and this mission was an early feat in the spaceborne exploration of outer space...

, Mars 1
Mars 1
Mars 1, also known as 1962 Beta Nu 1, Mars 2MV-4 and Sputnik 23, was an automatic interplanetary station launched in the direction of Mars on November 1, 1962, the first of the Soviet Mars probe program, with the intent of flying by the planet at a distance of about 11,000 km...

 and Pioneer 5
Pioneer 5
Pioneer 5 was a spin-stabilized space probe in the NASA Pioneer program used to investigate interplanetary space between the orbits of Earth and Venus. It was launched on March 11, 1960 from Cape Canaveral Air Force Station Launch Complex 17a at 13:00:00 UTC with an on-orbit dry mass of 43 kg...

) have carried micrometeoroid detectors.

In 1957 Hans Peterson conducted one of the first direct measurements of the fall of space dust on the Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, estimating it to be 14,300,000 tons per year. If this were true, then the Moon would be covered to a very great depth as there are limited forms of erosion to remove this material. In 1961 Arthur C. Clarke
Arthur C. Clarke
Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...

 popularized this possibility in his novel A Fall of Moondust
A Fall of Moondust
A Fall of Moondust is a hard science fiction novel by Arthur C. Clarke, first published in 1961. It was nominated for a Hugo Award for Best Novel, and was the first science fiction novel selected to become a Reader's Digest Condensed Book....

. This was cause for some concern among the groups attempting to land on the Moon, so a series of new studies followed to better characterize the issue. This included the launch of several spacecraft designed to directly measure the micrometeorite flux (Pegasus satellite program
Pegasus satellite program
The Pegasus satellite program was a series of three American satellites launched in 1965 to study the frequency of micrometeorite impacts on spacecraft...

) or directly measure the dust on the surface of the Moon (Surveyor Program
Surveyor program
The Surveyor Program was a NASA program that, from 1966 through 1968, sent seven robotic spacecraft to the surface of the Moon. Its primary goal was to demonstrate the feasibility of soft landings on the Moon...

). These showed that the flux was much lower than earlier estimates, around 10,000 to 20,000 tons per year, and that the surface of the Moon is relatively rocky.

Micrometeoroids have less stable orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

s than meteoroids, due to their greater surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...

 to mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 ratio. Micrometeoroids that fall to Earth can provide information on millimeter scale heating events in the solar nebula
Solar nebula
In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

. Micrometeorites
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

 (as they are known upon arrival at the Earth's surface) can only be collected in areas where there is no terrestrial sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

, typically polar regions. Ice is collected and then melted and filtered so the micrometeorites can be extracted under a microscope.

Sufficiently small micrometeoroids avoid significant heating on entry into the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. Collection of such particles by high flying aircraft began in the 1970s, since which time these samples of stratosphere-collected interplanetary dust (called Brownlee particles before their extraterrestrial origin was confirmed) have become an important component of the extraterrestrial materials
Extraterrestrial materials
Most atoms on Earth came from the interstellar dust and gas from which the Sun and Solar System formed. However, in the space science community, "extraterrestrial materials" generally refers to objects now on Earth that were solidified prior to arriving on earth...

 available for study in laboratories on Earth.

Effect on spacecraft operations

Micrometeoroids pose a significant threat to space exploration. Their velocities relative to a spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 in orbit can be on the order of kilometers per second, and resistance to micrometeoroid impact is a significant design challenge for spacecraft and space suit
Space suit
A space suit is a garment worn to keep an astronaut alive in the harsh environment of outer space. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extra-vehicular activity , work done outside spacecraft...

 designers (See Thermal Micrometeoroid Garment
Thermal Micrometeoroid Garment
An Thermal Micrometeoroid Garment is the outer layer of a space suit. The TMG has three functions: to insulate the suit occupant and prevent heat loss, to shield the occupant from harmful solar radiation, and to protect the astronaut from micrometeoroids and other orbital debris, which could...

). While the tiny sizes of most micrometeoroids limits the damage incurred, the high velocity impacts will constantly degrade the outer casing of spacecraft in a manner analogous to sandblasting. Long term exposure can threaten the functionality of spacecraft systems.

Impacts by small objects with extremely high velocity are a current area of research in terminal ballistics
Terminal ballistics
Terminal ballistics, a sub-field of ballistics, is the study of the behavior of a projectile when it hits its target. It is often referred to as stopping power when dealing with human or other living targets. Terminal ballistics is relevant both for small caliber projectiles as well as for large...

. Accelerating objects up to such velocities is difficult; current techniques include linear motor
Linear motor
A linear motor is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque it produces a linear force along its length...

s and shaped charge
Shaped charge
A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to cut and form metal, to initiate nuclear weapons, to penetrate armor, and in the oil and gas industry...

s. The risk is especially high for objects in space for long periods of time, such as satellites. They also pose major engineering challenges in theoretical low-cost lift systems such as rotovators, space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...

s, and orbital airship
Orbital airship
The orbital airship, also called the space blimp, is a proposed space transportation system that carries payloads to and from low Earth orbit...


External links

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