That cyclic process of growth and destruction outside of the clouds has been modeled   to demonstrate that the cores live much longer than the average lifetime of dust mass. Those cores mostly start with silicate particles condensing in the atmospheres of cool, oxygen-rich red-giants and carbon grains condensing in the atmospheres of cool carbon stars.
Red giants have evolved or altered off the main sequence and have entered the giant phase of their evolution and are the major source of refractory dust grain cores in galaxies. Those refractory cores are also called stardust section above , which is a scientific term for the small fraction of cosmic dust that condensed thermally within stellar gases as they were ejected from the stars. Several percent of refractory grain cores have condensed within expanding interiors of supernovae, a type of cosmic decompression chamber. Meteoriticists who study refractory stardust extracted from meteorites often call it presolar grains but that within meteorites is only a small fraction of all presolar dust.
Stardust condenses within the stars via considerably different condensation chemistry than that of the bulk of cosmic dust, which accretes cold onto preexisting dust in dark molecular clouds of the galaxy. Those molecular clouds are very cold, typically less than 50K, so that ices of many kinds may accrete onto grains, in cases only to be destroyed or split apart by radiation and sublimation into a gas component. Finally, as the Solar System formed many interstellar dust grains were further modified by coalescence and chemical reactions in the planetary accretion disk.
The history of the various types of grains in the early Solar System is complicated and only partially understood. Astronomers know that the dust is formed in the envelopes of late-evolved stars from specific observational signatures. In infrared light, emission at 9. Emission at These help provide evidence that the small silicate particles in space came from the ejected outer envelopes of these stars. Conditions in interstellar space are generally not suitable for the formation of silicate cores.
This would take excessive time to accomplish, even if it might be possible. The arguments are that: given an observed typical grain diameter a , the time for a grain to attain a , and given the temperature of interstellar gas, it would take considerably longer than the age of the Universe for interstellar grains to form. So mass loss from stars is unquestionably where the refractory cores of grains formed. Most dust in the Solar System is highly processed dust, recycled from the material out of which the Solar System formed and subsequently collected in the planetesimals, and leftover solid material such as comets and asteroids , and reformed in each of those bodies' collisional lifetimes.
During the Solar System's formation history, the most abundant element was and still is H 2. The metallic elements: magnesium, silicon, and iron, which are the principal ingredients of rocky planets, condensed into solids at the highest temperatures of the planetary disk.
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Some molecules, for example, graphite C and SiC would condense into solid grains in the planetary disk; but carbon and SiC grains found in meteorites are presolar based on their isotopic compositions, rather than from the planetary disk formation. Some molecules also formed complex organic compounds and some molecules formed frozen ice mantles, of which either could coat the "refractory" Mg, Si, Fe grain cores.
Stardust once more provides an exception to the general trend, as it appears to be totally unprocessed since its thermal condensation within stars as refractory crystalline minerals. The condensation of graphite occurs within supernova interiors as they expand and cool, and do so even in gas containing more oxygen than carbon,  a surprising carbon chemistry made possible by the intense radioactive environment of supernovae.
This special example of dust formation has merited specific review. Planetary disk formation of precursor molecules was determined, in large part, by the temperature of the solar nebula. Since the temperature of the solar nebula decreased with heliocentric distance, scientists can infer a dust grain's origin s with knowledge of the grain's materials.
Some materials could only have been formed at high temperatures, while other grain materials could only have been formed at much lower temperatures.
Inventory of Cosmic Carbon
The materials in a single interplanetary dust particle often show that the grain elements formed in different locations and at different times in the solar nebula. Most of the matter present in the original solar nebula has since disappeared; drawn into the Sun, expelled into interstellar space, or reprocessed, for example, as part of the planets, asteroids or comets.
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Due to their highly processed nature, IDPs interplanetary dust particles are fine-grained mixtures of thousands to millions of mineral grains and amorphous components. We can picture an IDP as a "matrix" of material with embedded elements which were formed at different times and places in the solar nebula and before the solar nebula's formation.
The arrows in the adjacent diagram show one possible path from a collected interplanetary dust particle back to the early stages of the solar nebula. We can follow the trail to the right in the diagram to the IDPs that contain the most volatile and primitive elements.
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The trail takes us first from interplanetary dust particles to chondritic interplanetary dust particles. Planetary scientists classify chondritic IDPs in terms of their diminishing degree of oxidation so that they fall into three major groups: the carbonaneous, the ordinary, and the enstatite chondrites.
As the name implies, the carbonaceous chondrites are rich in carbon, and many have anomalies in the isotopic abundances of H, C, N, and O Jessberger, [ citation needed ]. From the carbonaceous chondrites, we follow the trail to the most primitive materials. They are almost completely oxidized and contain the lowest condensation temperature elements "volatile" elements and the largest amount of organic compounds. Therefore, dust particles with these elements are thought to be formed in the early life of the Solar System.
The volatile elements have never seen temperatures above about K, therefore, the IDP grain "matrix" consists of some very primitive Solar System material. Such a scenario is true in the case of comet dust. Nuclear damage tracks are caused by the ion flux from solar flares. Solar wind ions impacting on the particle's surface produce amorphous radiation damaged rims on the particle's surface.
The Physics of Interstellar Dust
And spallogenic nuclei are produced by galactic and solar cosmic rays. A dust particle that originates in the Kuiper Belt at 40 AU would have many more times the density of tracks, thicker amorphous rims and higher integrated doses than a dust particle originating in the main-asteroid belt. Based on computer model studies , the complex organic molecules necessary for life Extraterrestrial organic molecules may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth. In September , NASA scientists reported that polycyclic aromatic hydrocarbons PAHs , subjected to interstellar medium ISM conditions, are transformed, through hydrogenation , oxygenation and hydroxylation , to more complex organics — "a step along the path toward amino acids and nucleotides , the raw materials of proteins and DNA , respectively".
In February , NASA announced a greatly upgraded database   for detecting and monitoring polycyclic aromatic hydrocarbons PAHs in the universe. In March , NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life , including uracil , cytosine and thymine , have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine , found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons PAHs , the most carbon-rich chemical found in the Universe , may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists.
The Solar System has its own interplanetary dust cloud , as do extrasolar systems. There are different types of nebulae with different physical causes and processes: diffuse nebula , infrared IR reflection nebula , supernova remnant , molecular cloud , HII regions , photodissociation regions , and dark nebula. Distinctions between those types of nebula are that different radiation processes are at work. For example, H II regions, like the Orion Nebula , where a lot of star-formation is taking place, are characterized as thermal emission nebulae.
Supernova remnants, on the other hand, like the Crab Nebula , are characterized as nonthermal emission synchrotron radiation. Reference Cat. The Discovery program's Stardust mission , was launched on 7 February to collect samples from the coma of comet Wild 2 , as well as samples of cosmic dust. It returned samples to Earth on 15 January In the spring of , the recovery of particles of interstellar dust from the samples was announced. From Wikipedia, the free encyclopedia. For other uses, see Space dust disambiguation.
For the jazz band, see Cosmic Dust band. Dust floating in space. Main article: Presolar grains. Astronomy portal. Accretion Astrochemistry Atomic and molecular astrophysics Cosmochemistry Extraterrestrial materials Interstellar medium List of interstellar and circumstellar molecules Micrometeoroid Tanpopo , a mission that collected cosmic dust in low Earth orbit. Compound-specific carbon isotope data of measured purine and pyrimidine compounds indicated a nonterrestrial origin for these compounds see Fig. Consequently, nucleobases delivered to these worlds together with sugar- related species and amino acids might have been beneficial to the origin of life on Earth, Mars, or elsewhere.
Observations of cometary comae indicate that comets are rich in organic compounds and will have effectively delivered carbonaceous solids and volatiles to the surface of young planets. In contrast, the endogenous synthesis of prebiotic organic compounds may have been constrained by the conditions on the young Earth. Whatever the inventory of endogenous organic compounds on the ancient Earth, it would have been augmented by extraterrestrial material. Several compounds are observed ubiquitously in our and external galaxies. The position of this feature attributed to amorphous carbon compounds is practically invariant in galactic and extragalactic regions, which argues for an abundant and stable carrier.
Understanding the implications of extraterrestrial delivery requires substantial knowledge of planetary dynamics, disk and solar nebula chemistry. There is a huge difference between making or discovering amino acids in space and creating life and the origin of life and the survival of existing life through adaptation in apparently impossible environments. It is questionable if the most abundant organic material, namely aromatic hydrocarbons and carbonaceous networks are formed only in circumstellar environments. Exploring mechanisms to form aromatics in the low temperature diffuse interstellar medium represent an important research avenue.
The infrared emission bands that have identified aromatic compounds in galactic and extragalactic regions sample multi-cloud lines of sight and consequently a size and shape and likely ionization state distribution of PAHs.
The identification of individual PAH molecules through their vibrational transitions will be very difficult. Only a combination of observations, laboratory data and theoretical calculations will provide constraints for the identification of a specific PAH class or family. Small bodies, such as comets, asteroids and their fragments, meteorites and interplanetary dust particles IDPs bear witness of processes occurring at the time of solar system formation.
These research avenues will also guide us to extend our knowledge to other habitable worlds. Additional Perspectives on The Origins of Life available at www. Figure 1. Previous Section Next Section. View this table: In this window In a new window.
Formation of Carbon Compounds in Space Environments Interstellar molecules can be identified through their electronic transition in the UV and optical part of the spectrum or in the infrared range through vibrational transitions. Solar System Formation Interstellar matter provides the raw material for the formation of stars and planets.
Extraterrestrial Delivery The large quantities of extraterrestrial material delivered to young terrestrial planetary surfaces in the early history of our solar system may have provided the material necessary for the emergence of life Chyba et al. Gas Phase Molecules Polycyclic aromatic hydrocarbons PAHs are composed of aromatic rings and are characterized by a high stability against radiation, in particular when in pericondensed form.
Figure 2. Figure 3. Refractory Compounds Carbon solids are ubiquitous material in interstellar space. Interstellar Ices Ground-based observations revealed already decades ago abundant water ice as well as CO e. Stability of Organic Molecules To understand what compounds can survive solar system formation or extraterrestrial delivery the thermal and radiation stability of organic compounds and biomolecules has to be investigated in laboratory studies.
Prebiotic Molecules in Space—Any Relevance for Early Earth Aromatic molecules and biomarkers are widespread in our galaxy and beyond Ehrenfreund et al. Figure 4. Previous Section.