Extraterrestrial material refers to natural objects now on Earth that originated in outer space. Such materials include

cosmic dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...

and meteorites, as well as samples brought to Earth by

sample return mission A sample-return mission is a spacecraft mission to collect and return samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as lo ...

s from the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, asteroids and

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

s, as well as

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

particles. Extraterrestrial materials are of value to science as they preserve the primitive composition of the

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

and dust from which the Sun and the Solar System formed.

Categories

Extraterrestrial material for study on earth can be classified into a few broad categories, namely: # Meteorites too large to vaporize on atmospheric entry but small enough to leave fragments lying on the ground, among which are included likely specimens from the asteroid and Kuiper belts as well as from the moon and from Mars. # Moon rocks brought to Earth by robotic and crewed lunar missions. #

Cosmic dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...

collected on Earth, in the Earth's stratosphere, and in

low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...

which likely include particles from the present day interplanetary dust cloud, as well as from comets. # Specimens collected by sample-return missions from

s, asteroids,

, which include "stardust particles" from the present-day interstellar medium. #

Presolar grains Presolar grains are interstellar solid matter in the form of tiny solid grains that originated at a time before the Sun was formed. Presolar stardust grains formed within outflowing and cooling gases from earlier presolar stars. The stellar nucl ...

(extracted from meteorites and interplanetary dust particles) that predate the formation of the Solar System. These are the most pristine and valuable samples.

Collected on Earth

Examples of extraterrestrial material collected on Earth include

and meteorites. Some of the meteorites found on Earth had their origin in another Solar System object such as the

Martian meteorite A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a percen ...

s,Meteoritical Bulletin Database
/ref> and the HED meteorite from Vesta. Another example is the Japanese

Tanpopo was a sub-group of the Japanese idol girl group Morning Musume and associated with Hello! Project. It was formed by Up-Front Promotion in November 1998 as Morning Musume's first sub-group. While the main group Morning Musume features predomin ...

mission that collected dust from low Earth orbit.) and the asteroid Itokawa ( ''Hayabusa'' mission) have each been visited by robotic spacecraft that returned samples to Earth, and samples of the

were also returned by the robotic ''Genesis'' mission. Current sample-return missions are

OSIRIS-REx OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is a NASA asteroid-study and sample-return mission. The mission's primary goal is to obtain a sample of at least from 101955 Bennu, a carbona ...

to asteroid

Bennu Bennu is an ancient Egyptian deity linked with the Sun, creation, and rebirth. He may have been the original inspiration for the phoenix legends that developed in Greek mythology. Roles According to Egyptian mythology, Bennu was a self-create ...

, and '' Hayabusa2'' to asteroid Ryugu. Several sample-return mission are planned for the Moon, Mars, and Mars' moons (see: Sample-return mission#List of missions). Material obtained from sample-return missions are considered pristine and uncontaminated, and their curation and study must take place at specialized facilities where the samples are protected from Earthly contamination and from contact with the atmosphere. These facilities are specially designed to preserve both the sample integrity and protect the Earth from potential biological contamination. Restricted bodies include planets or moons suspected to have either past or present habitable environments to microscopic life, and therefore must be treated as extremely

biohazard A biological hazard, or biohazard, is a biological substance that poses a threat to the health of living organisms, primarily humans. This could include a sample of a microorganism, virus or toxin that can adversely affect human health. A bioh ...

ous.

Lines of study

Samples analyzed on Earth can be matched against findings of remote sensing, for more insight into the processes that formed the Solar System.

Elemental and isotopic abundances

Present day

elemental abundances An elemental is a mythic being that is described in occult and alchemical works from around the time of the European Renaissance, and particularly elaborated in the 16th century works of Paracelsus. According to Paracelsus and his subsequent fo ...

are superimposed on an (evolving) galactic-average set of elemental abundances that was inherited by the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, along with some atoms from local

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

sources, at the time of the Sun's formation. Knowledge of these average planetary system

is serving as a tool for tracking chemical and physical processes involved in the formation of planets, and the evolution of their surfaces. Isotopic abundances provide important clues to the origin, transformation and geologic age of the material being analyzed. Extraterrestrial materials also carry information on a wide range of nuclear processes. These include for example: (i) the decay of now-extinct radionuclides from supernova byproducts introduced into Solar System materials shortly before the collapse of our solar nebula, and (ii) the products of stellar and explosive nucleosynthesis found in almost undiluted form in

presolar grains Presolar grains are interstellar solid matter in the form of tiny solid grains that originated at a time before the Sun was formed. Presolar stardust grains formed within outflowing and cooling gases from earlier presolar stars. The stellar nucl ...

. The latter are providing astronomers with information on exotic environments from the early

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galaxy.

Noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...

es are particularly useful because they avoid chemical reactions, secondly because many of them have more than one isotope on which to carry the signature of nuclear processes, and because they are relatively easy to extract from solid materials by simple heating. As a result, they play a pivotal role in the study of extraterrestrial materials.

Nuclear spallation effects

Particles subject to bombardment by sufficiently energetic particles, like those found in cosmic rays, also experience the transmutation of atoms of one kind into another. These spallation effects can alter the trace element isotopic composition of specimens in ways which allow researchers to deduct the nature of their exposure in space. These techniques have been used, for example, to look for (and determine the date of) events in the pre-Earth history of a meteorite's parent body (like a major collision) that drastically altered the space exposure of the material in that meteorite. For example, the

Murchison meteorite The Murchison meteorite is a meteorite that fell in Australia in 1969 near Murchison, Victoria. It belongs to the carbonaceous chondrite class, a group of meteorites rich in organic compounds. Due to its mass (over ) and the fact that it was an ...

landed in Australia in 1967, but its parent body apparently underwent a collision event about 800,000 years ago which broke it into meter-sized pieces.

Astrobiology

Astrobiology is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of

life Life is a quality that distinguishes matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes, from that which does not, and is defined by the capacity for Cell growth, growth, reaction to Stimu ...

in the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. ...

. It involves investigations on the presence of the

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...

s on comets, asteroids, Mars or the moons of the

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

s. Several sample-return missions to asteroids and comets are currently in the works with a key interest in astrobiology. More samples from asteroids, comets and moons could help determine whether life formed in other astronomical bodies, and if it could have been carried to Earth by meteorites or comets — a process termed

panspermia Panspermia () is the hypothesis, first proposed in the 5th century BCE by the Greek philosopher Anaxagoras, that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and planetoids, as well as by spacec ...

. The abundant

s in primitive meteorites and interplanetary dust particles are thought to originate largely in the interstellar medium. However, this material may have been modified in the protoplanetary disk and has been modified to varying extents in the asteroidal parent bodies.

contains complex organic compounds (amorphous organic solids with a mixed

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...

structure) that can be created naturally by

stars A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth ma ...

and radiation. These compounds, in the presence of water and other habitable factors, are thought to have produced and spontaneously assembled the building blocks of life.

Origin of water on Earth

The origin of water on Earth is the subject of a significant body of research in the fields of planetary science,

astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...

, and astrobiology. Isotopic ratios provide a unique "chemical fingerprint" that is used to compare Earth's water with reservoirs elsewhere in the Solar System. One such isotopic ratio, that of

deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...

to hydrogen (D/H), is particularly useful in the search for the origin of water on Earth. However, when and how that water was delivered to Earth is the subject of ongoing research.

References

External links

Planetary Science Research Discoveries
Educational journal with articles about extraterrestrial materials. {{DEFAULTSORT:Extraterrestrial material Meteorite mineralogy and petrology Lunar science Space science Planetary science Interstellar media