Presolar grains
Encyclopedia
Presolar grains are isotopically-distinct clusters of material found in the fine-grained matrix
of primitive meteorites, such as chondrites, whose differences from the surrounding meteorite suggest that they are older than the solar system
. Crystallinity in these clusters ranges from that of micrometre-sized silicon carbide
crystals, down to that of diamond and unlayered graphene crystals with fewer than 100 atoms. These grains were probably formed in supernova
e or the stellar outflows of red giant
stars, and then incorporated into the molecular cloud from which the solar nebula
separated to form our solar system. Presolar grains identified so far consist of refractory
mineral
s which survived the collapse of the solar nebula, and the subsequent formation of planetesimal
s.
In the 1960s, neon
and xenon
components with unusual isotopic ratio
s were discovered in primitive meteorites. One possible explanation: The existence of intact presolar grains containing anomalous noble gas within these meteorites.
In 1987 diamond and silicon carbide grains were found to be carriers of these noble gases. Significant major-element isotopic anomalies were in turn found within these grains.
Because identified presolar stardust grains formed in the neighborhood of specific stellar nucleosynthesis sources, the isotopic composition of their elements is usually different from the isotopic composition of solar-system matter as well as from the galactic average. These isotopic signatures often fingerprint very specific astrophysical nuclear processes, and thus they go beyond proving interstellar origin to providing independent insight into the way stars work.
s (SEM/TEM), and mass spectrometric methods (noble gas mass spectrometry, resonance ionization mass spectrometry (RIMS), secondary ion mass spectrometry
(SIMS, NanoSIMS)). Presolar grains that consist of diamonds are only a few nanometers in size, and are therefore also called nanodiamonds. Because of their small size, nanodiamonds are hard to investigate and, although they are among the first presolar grains discovered, relatively little is known about them. The typical sizes of other presolar grains are in the range of micrometres. Presolar grains represent material from outside our solar system.
and stellar evolution
. Grains bearing the isotopic signature of rapid-process
nucleosynthesis are useful in testing models of supernovae explosions. Other grains provide isotopic and physical information on asymptotic giant branch
stars, which have manufactured the lion's share of the refractory elements lighter than iron in the galaxy. Because the elements in these particles were made at different times (and places) in the early Milky Way, the set of collected particles further provides insight into galactic evolution
prior to formation of our solar system.
Along with providing information on nucleosynthesis, solid grains provide information on the physico-chemical conditions under which they formed, and on events subsequent to their formation. For example consider red giant
s - which produce much of the carbon in our galaxy. Their atmospheres are cool enough for condensation processes to take place - resulting in the precipitation of solid particles (i.e. multiple atom agglomerations of elements - such as Carbon) - in their atmosphere. This is unlike the atmosphere of our sun, which is too hot to allow build-up of atoms to form more complex molecules. These solid fragments of matter, are then injected into the interstellar medium by radiation pressure
. Hence particles bearing the signature of stellar nucleosynthesis are providing us with information on: (i) condensation processes in red giant atmospheres, (ii) radiation and heating processes in the interstellar medium
, and (iii) the types of particles that carried the elements of which we are made across the galaxy to our Solar system.
Matrix (geology)
The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...
of primitive meteorites, such as chondrites, whose differences from the surrounding meteorite suggest that they are older than 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...
. Crystallinity in these clusters ranges from that of micrometre-sized silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
crystals, down to that of diamond and unlayered graphene crystals with fewer than 100 atoms. These grains were probably formed in supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
e or the stellar outflows of red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
stars, and then incorporated into the molecular cloud from which 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...
separated to form our solar system. Presolar grains identified so far consist of refractory
Refractory
A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s which survived the collapse of the solar nebula, and the subsequent formation of planetesimal
Planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger...
s.
In the 1960s, neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
and xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
components with unusual isotopic ratio
Isotopic signature
An isotopic signature is a ratio of stable or unstable isotopes of particular elements found in an investigated material...
s were discovered in primitive meteorites. One possible explanation: The existence of intact presolar grains containing anomalous noble gas within these meteorites.
In 1987 diamond and silicon carbide grains were found to be carriers of these noble gases. Significant major-element isotopic anomalies were in turn found within these grains.
Because identified presolar stardust grains formed in the neighborhood of specific stellar nucleosynthesis sources, the isotopic composition of their elements is usually different from the isotopic composition of solar-system matter as well as from the galactic average. These isotopic signatures often fingerprint very specific astrophysical nuclear processes, and thus they go beyond proving interstellar origin to providing independent insight into the way stars work.
Types of presolar material
There are different types of presolar . Presolar grains consisting of the following minerals have so far been identified:- diamondDiamondIn mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
(C) nanometer-sized grains (~ 2.6 nm diameter) possibly formed by vapor deposition - graphiteGraphiteThe mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
(C) particles and onions, some with unlayered grapheneGrapheneGraphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...
cores - silicon carbideSilicon carbideSilicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
(SiC) submicrometer to micrometer sized grains. Presolar SiC occurs as single-polytype grains or polytype intergrowths. The atomic structures observed contain the two lowest order polytypes: hexagonal 2H and cubic 3C (with varying degrees of stacking fault disorder) as well as 1-dimensionally disordered SiC grains. In comparison, terrestrial laboratory synthesized SiC is known to form over a hundred different polytypes. - titanium carbideTitanium carbideTitanium carbide, TiC, is an extremely hard refractory ceramic material, similar to tungsten carbide.It is commercially used in tool bits. It has the appearance of black powder with NaCl-type face centered cubic crystal structure...
(TiC) and other carbides within C and SiC grains - silicon nitrideSilicon nitrideSilicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...
(Si3N4) - corundumCorundumCorundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red...
(Al2O3) - spinelSpinelSpinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety.-Spinel group:...
(MgAl2O4) - hiboniteHiboniteHibonite is a brownish black mineral with a hardness of 7.5-8.0 and a hexagonal crystal structure. It is rare, but is found in high-grade metamorphic rocks on Madagascar. Some presolar grains in primitive meteorites consist of hibonite. Hibonite also is a common mineral in the Ca-Al-rich...
((Ca,Ce)(Al,Ti,Mg)12O19) - titanium oxideTitanium dioxideTitanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of...
(TiO2) - silicate mineralsSilicate mineralsThe silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
(olivineOlivineThe mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
and pyroxenePyroxeneThe pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
)
Characterization of presolar materials
Presolar grains are investigated using scanning or transmission electron microscopeElectron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...
s (SEM/TEM), and mass spectrometric methods (noble gas mass spectrometry, resonance ionization mass spectrometry (RIMS), secondary ion mass spectrometry
Secondary ion mass spectrometry
Secondary ion mass spectrometry is a technique used in materials science and surface science to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions...
(SIMS, NanoSIMS)). Presolar grains that consist of diamonds are only a few nanometers in size, and are therefore also called nanodiamonds. Because of their small size, nanodiamonds are hard to investigate and, although they are among the first presolar grains discovered, relatively little is known about them. The typical sizes of other presolar grains are in the range of micrometres. Presolar grains represent material from outside our solar system.
Information carried by presolar grains
The study of presolar grains provides information about nucleosynthesisNucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
and stellar evolution
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
. Grains bearing the isotopic signature of rapid-process
R-process
The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
nucleosynthesis are useful in testing models of supernovae explosions. Other grains provide isotopic and physical information on asymptotic giant branch
Asymptotic Giant Branch
The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass stars. This is a period of stellar evolution undertaken by all low to intermediate mass stars late in their lives....
stars, which have manufactured the lion's share of the refractory elements lighter than iron in the galaxy. Because the elements in these particles were made at different times (and places) in the early Milky Way, the set of collected particles further provides insight into galactic evolution
Galaxy formation and evolution
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...
prior to formation of our solar system.
Along with providing information on nucleosynthesis, solid grains provide information on the physico-chemical conditions under which they formed, and on events subsequent to their formation. For example consider red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
s - which produce much of the carbon in our galaxy. Their atmospheres are cool enough for condensation processes to take place - resulting in the precipitation of solid particles (i.e. multiple atom agglomerations of elements - such as Carbon) - in their atmosphere. This is unlike the atmosphere of our sun, which is too hot to allow build-up of atoms to form more complex molecules. These solid fragments of matter, are then injected into the interstellar medium by radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
. Hence particles bearing the signature of stellar nucleosynthesis are providing us with information on: (i) condensation processes in red giant atmospheres, (ii) radiation and heating processes in the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
, and (iii) the types of particles that carried the elements of which we are made across the galaxy to our Solar system.
See also
- cosmic dustCosmic dustCosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
- interplanetary dust cloudInterplanetary dust cloudThe interplanetary dust cloud is cosmic dust which pervades the space between planets in the Solar System and in other planetary systems...
- circumstellar dustCircumstellar dustCircumstellar Dust is astronomical dust around a star. It can be in the form of a spherical shell or a disk, e.g. an accretion disk. Circumstellar dust can be responsible for significant extinction and is usually the source of an infrared excess for stars that have it.The motion of circumstellar...
- extraterrestrial materialsExtraterrestrial materialsMost 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...
- cosmochemistryCosmochemistryCosmochemistry 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...
External links
- http://presolar.wustl.edu/work/grains.html
- http://www.astro.uiuc.edu/~akspeck/witch-stuff/Research/chapter3/node3.html
- http://www.ciw.edu/lrn/psg_main.html
- http://www.psrd.hawaii.edu/July97/Stardust.html
- http://www.stecf.org/~ralbrech/amico/intabs/ottu.html
- http://www.mpch-mainz.mpg.de/~kosmo/sims/sternenstaub/sternenstaub.htm (images of presolar grains, text in German)
- http://presolar.wustl.edu/~pgd (large database of isotopic data on presolar grains)
- Planetary Science Research Discoveries Educational journal with articles about presolar grains and cosmochemistry.