Extraterrestrial material refers to natural objects now on Earth that originated in outer space. Such materials include cosmic dust and meteorites, as well as samples brought to Earth by sample return missions from the Moon, asteroids and comets, as well as solar wind particles.
Extraterrestrial materials are of value to science as they preserve the primitive composition of the gas and dust from which the Sun and the Solar System formed.
Extraterrestrial material for study on earth can be classified into a few broad categories, namely:
Examples of extraterrestrial material collected on Earth include cosmic dust and meteorites. Some of the meteorites found on Earth had their origin in another Solar System object such as the Moon, [1] Martian meteorites, [2] [3] and the HED meteorite from Vesta. [4] [5] Another example is the Japanese Tanpopo mission that collected dust from low Earth orbit. [6] In 2019, researchers found interstellar dust in Antarctica which they relate to the Local Interstellar Cloud. The detection of interstellar dust in Antarctica was done by the measurement of the radionuclides Fe-60 and Mn-53 by highly sensitive Accelerator mass spectrometry, where Fe-60 is the clear signature for a recent-supernova origin. [7]
To date, samples of Moon rock have been collected by robotic and crewed missions. The comet Wild 2 (Genesis mission) and the asteroid Itokawa (Hayabusa mission) have each been visited by robotic spacecraft that returned samples to Earth, and samples of the solar wind were also returned by the robotic Genesis mission. [8] [9]
Current sample-return missions are OSIRIS-REx to asteroid Bennu, [10] [11] and Hayabusa2 to asteroid Ryugu. [12] 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. [13] [14] [15] [16] 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 biohazardous. [17] [18]
Samples analyzed on Earth can be matched against findings of remote sensing, for more insight into the processes that formed the Solar System.
Present day elemental abundances are superimposed on an (evolving) galactic-average set of elemental abundances that was inherited by the Solar System, along with some atoms from local nucleosynthesis sources, at the time of the Sun's formation. [19] [20] [21] Knowledge of these average planetary system elemental abundances is serving as a tool for tracking chemical and physical processes involved in the formation of planets, and the evolution of their surfaces. [20]
Isotopic abundances provide important clues to the origin, transformation and geologic age of the material being analyzed. [22]
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, [23] and (ii) the products of stellar and explosive nucleosynthesis found in almost undiluted form in presolar grains. [24] The latter are providing astronomers with information on exotic environments from the early Milky Way galaxy.
Noble gases 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. [25]
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.[ citation needed ]
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 landed in Australia in 1967, but its parent body apparently underwent a collision event about 800,000 years ago [26] which broke it into meter-sized pieces.
Astrobiology is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of life in the universe. It involves investigations on the presence of the organic compounds on comets, asteroids, Mars or the moons of the gas giants. 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. [27] [28] [29]
The abundant organic compounds 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. [30]
Cosmic dust contains complex organic compounds (amorphous organic solids with a mixed aromatic-aliphatic structure) that can be created naturally by stars and radiation. [31] [32] [33] These compounds, in the presence of water and other habitable factors, are thought to have produced and spontaneously assembled the building blocks of life. [34] [35]
The origin of water on Earth is the subject of a significant body of research in the fields of planetary science, astronomy, 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 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. [36] [37]
Astrobiology is a scientific field within the life and environmental sciences that studies the origins, early evolution, distribution, and future of life in the universe by investigating its deterministic conditions and contingent events. As a discipline, astrobiology is founded on the premise that life may exist beyond Earth.
Panspermia is the hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, and planetoids, as well as by spacecraft carrying unintended contamination by microorganisms. Panspermia is a fringe theory with little support amongst mainstream scientists. Critics argue that it does not answer the question of the origin of life but merely places it on another celestial body. It is also criticized because it cannot be tested experimentally.
Astrochemistry is the study of the abundance and reactions of molecules in the universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form.
Stardust was a 385-kilogram robotic space probe launched by NASA on 7 February 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return them to Earth for analysis. It was the first sample return mission of its kind. En route to Comet Wild 2, it also flew by and studied the asteroid 5535 Annefrank. The primary mission was successfully completed on 15 January 2006 when the sample return capsule returned to Earth.
Cosmochemistry or chemical cosmology is the study of the chemical composition of matter in the universe and the processes that led to those compositions. This is done primarily through the study of the chemical composition of meteorites and other physical samples. Given that the asteroid parent bodies of meteorites were some of the first solid material to condense from the early solar nebula, cosmochemists are generally, but not exclusively, concerned with the objects contained within the Solar System.
A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. The IAU officially defines meteorites as 30 micrometers to 1 meter; micrometeorites are the small end of the range (~submillimeter). They are a subset of cosmic dust, which also includes the smaller interplanetary dust particles (IDPs).
Cosmic dust – also called extraterrestrial dust, space dust, or star dust – is dust that occurs in outer space or has fallen onto Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 μm), such as micrometeoroids. Larger particles are called meteoroids. Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust, and circumplanetary dust. There are several methods to obtain space dust measurement.
The interplanetary dust cloud, or zodiacal cloud, consists of cosmic dust that pervades the space between planets within planetary systems, such as the Solar System. This system of particles has been studied for many years in order to understand its nature, origin, and relationship to larger bodies. There are several methods to obtain space dust measurement.
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 loose material and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation or a collector array used for capturing particles of solar wind or cometary debris. Nonetheless, concerns have been raised that the return of such samples to planet Earth may endanger Earth itself.
David Stewart McKay was chief scientist for astrobiology at the Johnson Space Center. During the Apollo program, McKay provided geology training to the first men to walk on the Moon in the late 1960s. McKay was the first author of a scientific paper postulating past life on Mars on the basis of evidence in Martian meteorite ALH 84001, which had been found in Antarctica. This paper has become one of the most heavily cited papers in planetary science. The NASA Astrobiology Institute was founded partially as a result of community interest in this paper and related topics. He was a native of Titusville, Pennsylvania.
CI chondrites, also called C1 chondrites or Ivuna-type carbonaceous chondrites, are a group of rare carbonaceous chondrite, a type of stony meteorite. They are named after the Ivuna meteorite, the type specimen. CI chondrites have been recovered in France, Canada, India, and Tanzania. Their overall chemical composition closely resembles the elemental composition of the Sun, more so than any other type of meteorite.
Interplanetary contamination refers to biological contamination of a planetary body by a space probe or spacecraft, either deliberate or unintentional.
A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets, dwarf planets, natural satellites, planetesimals and many other small Solar System bodies (SSSBs). The study of planetary surfaces is a field of planetary geology known as surface geology, but also a focus on a number of fields including planetary cartography, topography, geomorphology, atmospheric sciences, and astronomy. Land is the term given to non-liquid planetary surfaces. The term landing is used to describe the collision of an object with a planetary surface and is usually at a velocity in which the object can remain intact and remain attached.
Comparative planetary science or comparative planetology is a branch of space science and planetary science in which different natural processes and systems are studied by their effects and phenomena on and between multiple bodies. The planetary processes in question include geology, hydrology, atmospheric physics, and interactions such as impact cratering, space weathering, and magnetospheric physics in the solar wind, and possibly biology, via astrobiology.
The Tanpopo mission is an orbital astrobiology experiment investigating the potential interplanetary transfer of life, organic compounds, and possible terrestrial particles in the low Earth orbit. The purpose is to assess the panspermia hypothesis and the possibility of natural interplanetary transport of microbial life as well as prebiotic organic compounds.
The curation of extraterrestrial samples (astromaterials) obtained by sample-return missions takes place at facilities specially designed to preserve both the sample integrity and protect the Earth. Astromaterials are classified as either non-restricted or restricted, depending on the nature of the Solar System body. Non-restricted samples include the Moon, asteroids, comets, solar particles and space dust. 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 biohazardous.
Asteroidal water is water or water precursor deposits such as hydroxide (OH−) that exist in asteroids. The "snow line" of the Solar System lies outside of the main asteroid belt, and the majority of water is expected in minor planets. Nevertheless, a significant amount of water is also found inside the snow line, including in near-earth objects (NEOs).
Pseudo-panspermia is a well-supported hypothesis for a stage in the origin of life. The theory first asserts that many of the small organic molecules used for life originated in space. It continues that these organic molecules were distributed to planetary surfaces, where life then emerged on Earth and perhaps on other planets. Pseudo-panspermia differs from the fringe theory of panspermia, which asserts that life arrived on Earth from distant planets.
Space dust measurement refers to the study of small particles of extraterrestrial material, known as micrometeoroids or interplanetary dust particles (IDPs), that are present in the Solar System. These particles are typically of micrometer to sub-millimeter size and are composed of a variety of materials including silicates, metals, and carbon compounds. The study of space dust is important as it provides insight into the composition and evolution of the Solar System, as well as the potential hazards posed by these particles to spacecraft and other space-borne assets. The measurement of space dust requires the use of advanced scientific techniques such as secondary ion mass spectrometry (SIMS), optical and atomic force microscopy (AFM), and laser-induced breakdown spectroscopy (LIBS) to accurately characterize the physical and chemical properties of these particles.
Dust astronomy is a subfield of astronomy that uses the information contained in individual cosmic dust particles ranging from their dynamical state to its isotopic, elemental, molecular, and mineralogical composition in order to obtain information on the astronomical objects occurring in outer space. Dust astronomy overlaps with the fields of Planetary science, Cosmochemistry, and Astrobiology.
A Sample Return Facility will require combining technologies used for constructing maximum containment laboratories (e.g. Biosafety level 4 labs) with cleanroom technologies which will be needed to protect the Mars samples from Earth contamination.