Organic Compounds in Circumstellar and Interstellar Environments

Abstract

Recent research has discovered that complex organic matter is prevalent throughout the Universe. In the Solar System, it is found in meteorites, comets, interplanetary dust particles, and planetary satellites. Spectroscopic signatures of organics with aromatic/aliphatic structures are also found in stellar ejecta, diffuse interstellar medium, and external galaxies. From space infrared spectroscopic observations, we have found that complex organics can be synthesized in the late stages of stellar evolution. Shortly after the nuclear synthesis of the element carbon, organic gas-phase molecules are formed in the stellar winds, which later condense into solid organic particles. This organic synthesis occurs over very short time scales of about a thousand years. In order to determine the chemical structures of these stellar organics, comparisons are made with particles produced in the laboratory. Using the technique of chemical vapor deposition, artificial organic particles have been created by injecting energy into gas-phase hydrocarbon molecules. These comparisons led us to believe that the stellar organics are best described as amorphous carbonaceous nanoparticles with mixed aromatic and aliphatic components. The chemical structures of the stellar organics show strong similarity to the insoluble organic matter found in meteorites. Isotopic analysis of meteorites and interplanetary dust collected in the upper atmospheres have revealed the presence of pre-solar grains similar to those formed in old stars. This provides a direct link between star dust and the Solar System and raises the possibility that the early Solar System was chemically enriched by stellar ejecta with the potential of influencing the origin of life on Earth.

Deciphering the Origin of Abiotic Organic Compounds on Earth: Review and Future Prospects

“…Carbon (C) is the 4th most abundant element in the Universe and highly complex organic compounds involving this element have been discovered on objects from the solar system and more distant galaxies (Kwok, 2009). Space remote sensing techniques, e.g., space infrared spectroscopy, have identified more than 150 molecules with stretching and bending modes of compounds with aromatic and aliphatic structures (Kwok, 2009(Kwok, , 2015. For research in astronomy, one of the most definite and surprising knowledge of molecular synthesis comes from circumstellar envelopes of evolved stars, from the asymptotic giant branch (AGB) stars to protoplanetary nebulae to planetary nebulae, over very short (∼10 3 yr) time scales.…”

“…For research in astronomy, one of the most definite and surprising knowledge of molecular synthesis comes from circumstellar envelopes of evolved stars, from the asymptotic giant branch (AGB) stars to protoplanetary nebulae to planetary nebulae, over very short (∼10 3 yr) time scales. Specifically, carbon is synthesized in the core of AGB stars by nucleosynthesis and then dredged up to the star surface, and, subsequently, new Cbearing molecules with increasing complexity are detected through infrared and millimeter-wave spectroscopy in the stellar winds ejected from these stars (Kwok, 2015). By these processes, simple molecules, such as acetylene (C 2 H 2 ), CN chains (HCN, HC 3 N, HC 5 N), and rings (C 3 H 2 ), are formed at first in the stellar winds of AGB stars, followed by the formation of di-acetylene, triacetylene, and the first aromatic molecule, benzene, in the proto-planetary nebula stage.…”

“…Geometric structures with different long-and short-range order can be created by varying the sp 2 /sp 3 hybridization ratios. Considering the widespread presence of carbon and hydrogen, such complex amorphous organic solids may be widely present in space, because the infrared spectra of MAON from planetary nebulae resemble these amorphous carbonaceous materials (Dischler et al, 1983;Kwok, 2015).…”

5 Minerals and the Emergence of Life

“…The advent of an atomistic understanding of chemistry at the beginning of the 20th century, however, dealt the death-blow to vitalism since there was nothing special to organic molecules as compared to their inorganic counterparts, apart from their higher structural complexity (a disputable claim in the light of some of the minerals we will discuss below) and no natural border between inorganic and organic chemistry could be defined. It is ironic that the detection of organic molecules in numerous extraterrestrial settings from the surface of Titan [3] through comet atmospheres [4] to interstellar space [5] is still systematically interpreted as evidence that the seed for life on Earth may have come from outer space rather than as showing that there is nothing special to complex hydrocarbons and that their synthesis is just chemistry.…”