Organic Molecules in Interstellar Space: Latest Advances

Abstract

Although first considered as too diluted for the formation of molecules in-situ and too harsh an environment for their survival, the interstellar medium has turned out to host a rich palette of molecular species: to date, 256 species, not counting isotopologues, have been identified. The last decade, and more particularly the last 2 years, have seen an explosion of new detections, including those of a number of complex organic species, which may be dubbed as prebiotic. Organic molecules have been discovered not just in interstellar clouds from the Solar neighbourhood, but also throughout the Milky-Way, as well as in nearby galaxies, or some of the most distant quasars. These discoveries were made possible by the completion of large sub-millimetre and radio facilities. Equipped with new generation receivers, those instruments have provided the orders of magnitude leap in sensitivity required to detect the vanishingly weak rotational lines that allowed the molecule identifications. Last 2 years, 30 prebiotic molecules have been detected in TMC-1, a dust-enshrouded gaseous cloud located at 400 light-years from the Sun in the Taurus constellation. Ten new molecular species, have been identified in the arm of a spiral galaxy seven billion light-yr distant, and 12 molecular species observed in a quasar at 11 billion light-yr. We present the latest spectral observations of this outlying quasar and discuss the implications of those detections in these 3 archetypal sources. The basic ingredients involved in the Miller-Urey experiment and related experiments (H2, H2O, CH4, NH3, CO, H2S, … ) appeared early after the formation of the first galaxies and are widespread throughout the Universe. The chemical composition of the gas in distant galaxies seems not much different from that in the nearby interstellar clouds. It presumably comprises, like for TMC-1, aromatic rings and complex organic molecules putative precursors of the RNA nucleobases, except the lines of such complex species are too weak to be detected that far.

Sources of Nitrogen-, Sulfur-, and Phosphorus-Containing Feedstocks for Prebiotic Chemistry in the Planetary Environment

“…Organic species are present in the interstellar medium; protoplanetary disks; interplanetary dust particles; and primitive bodies including asteroids, comets, and interplanetary dust particles (see [ 56 , 243 , 244 , 245 , 246 ] and references therein). Organic delivery from exogenous sources has been suggested in the past (see [ 247 , 248 , 249 ] and references therein) as potentially important in seeding planets with the ingredients for life.…”

Structure and evolution of interstellar carbonaceous dust. Insights from the laboratory

“…The first molecule in the polyyne series, C 4 H 2 , has been recently detected in the C rich AGB star IRC +10216 (Fonfría et al, 2018), and the first two polyynes, C 4 H 2 , C 6 H 2, and benzene were found in the protoplanetary nebula CRL 618 (Cernicharo et al, 2001), but the next steps toward the formation of polyaromatic molecules are largely unknown. As mentioned above, the first detection of a polyaromatic molecule, the bicyclic molecule indene, has taken place recently (Burkhardt et al, 2021;Cernicharo et al, 2021) in the molecular cloud TMC-1, an environment with a chemistry quite different from that of AGB and post AGB stars (Guélin and Cernicharo, 2022). To investigate the evolution of acetylene in the reactions with C atoms and C 2 dimers present in the inner shells of AGB stars, Santoro et al (2020) used the "Stardust" set up (Martínez et al, 2020 and Figure 5), but introduced C 2 H 2 , instead of H 2 , in the sputtering chamber.…”

PyQM/MM: a Python Interface for ONIOM(QM:MM) Calculations with the AMOEBA09 Polarizable Force Field to Study the Chemical Processes in the Interstellar Medium

“…Radical species in the ISM play a vital role in forming complex organic molecules (COMs). [25][26][27] To understand the chemical evolution in the ISM, it is essential to understand the elementary radical process, such as radical adsorption, diffusion and chemical reactions on the ice mantles of interstellar grains. Accumulation of the primary radicals on the icy grain surfaces may occur at very low temperatures (e.g., 10 K) in dark clouds.…”