Astrophysical and astrochemical insights into the origin of life

Proceedings of the International Astronomical Union, 2018

The present-day Earth with its innumerable life forms is a product of cosmic evolution starting with the formation of our galaxy and the dense gas clouds within it, and proceeding through the contraction of one of those clouds about 4.6 Gyr ago, first into filaments and then one or more protostellar disks, planets, and central stars, one of which was our Sun. Radioactive debris from a massive nearby star was included. The planets themselves formed through coagulation, accretion, and fragmentation of solid bodies. Habitability depends on a delicate balance between disk accretion by gravity and dispersal by the central star, which determine the size of the planet and its gaseous envelope, combined with a long period of stellar radiation, which has to disperse this envelope but leave a hospitable secondary atmosphere. The final step toward life involves even more complexity as self-replicating bio-molecules form with ever increasing stability.

The last 105 years of stellar evolution represents the most active period of synthesis of organic compounds in a star's life. Over 60 gas-phase molecules, including rings, radicals, and molecular ions have been identified by millimeter-wave and infrared spectroscopic observations through their rotational and vibrational transitions. Space infrared spectroscopic observations of emissions from the stretching and bending modes of aliphatic and aromatic compounds have revealed a continuous synthesis of organic material over a period of only a few thousand years. These organic gases and solids are ejected into the interstellar medium through stellar winds and spread all over the Galaxy. 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 evolved stars. This provides a direct link between star dust and the solar system and raises the possibility that the early solar system ...

International Journal of Astrobiology, 2009

Contrary to decades of astronomical thought, the interstellar medium in our galaxy, i.e. the material between the stars, is actually quite rich in molecular material. Gas phase molecules and condensed-phase molecular carriers have now been observed in many astrophysical environments, and a wide variety of chemical compounds have been identified-over 140 in the gaseous state. In fact, molecular material appears to follow a complex life cycle, which begins with the active chemistry in circumstellar ejecta of evolved stars. Some circumstellar environments are carbon-rich and produce a unique synthesis where compounds with multiple carbon-carbon bonds are created. Molecular material from circumstellar shells appears to survive as these objects evolve into planetary nebula and their ejecta become part of diffuse clouds. Diffuse clouds subsequently collapse into dense clouds, carrying along some fraction of the chemical imprint of previous formation processes. This cycling of molecular gas can provide dense clouds with C-rich starting material, which accelerates organic chemistry in these objects. Furthermore, many molecular clouds eventually collapse into protostellar disks and then solar systems. While some of the matter in the pre-solar nebula is processed into planets, other molecular material survives in near-pristine form in comets, meteorites, and interplanetary dust particles, as evidenced by unusual isotope ratios. These objects can bring select interstellar compounds to planetary surfaces via exogenous delivery, many which are organic in nature, and some containing the biogenic element, phosphorus. In fact, life is thought to have begun on Earth after the period of Late Heavy Bombardment, when delivery of interstellar matter was probably at its maximum. Therefore, interstellar chemistry may have had an influence on the early biochemistry that led to terrestrial life. This scenario and the possible biogenic pathways from stars to planetary systems will be discussed. New astronomical observations tracing the molecular life cycle will be presented.

PubPub, 2019

Heavy molecule spectroscopy is a developing subject, with new results from both the terrestrial laboratory and astronomical discovery in the 0.5-10 GHz range where heavy molecule spectral lines are easily distinguished. Dense clouds in space contain an astonishingly rich collection of both familiar and exotic molecules in various states of ionization and excitation. It means that there are many more ways to build large organic molecules in these environments than have been previously explored. These add to the number of paths available for making the complex organic molecules and other large molecular species that may be the precursors to life.

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2011

International Journal of Astrobiology, 2011

The origin of life and the origin of the Universe are among the most important problems of science and they might be inextricably linked. Hydro-gravitational-dynamics cosmology predicts hydrogen–helium gas planets in clumps as the dark matter of galaxies, with millions of planets per star. This unexpected prediction is supported by quasar microlensing of a galaxy and a flood of new data from space telescopes. Supernovae from stellar over-accretion of planets produce the chemicals (C, N, O, P, etc.) and abundant liquid-water domains required for first life and the means for wide scattering of life prototypes. Life originated following the plasma-to-gas transition between 2 and 20 Myr after the big bang, while planetary core oceans were between critical and freezing temperatures, and interchanges of material between planets constituted essentially a cosmological primordial soup. Images from optical, radio and infrared space telescopes suggest life on Earth was neither first nor inevit...

Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 2015

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 cre...

The Astrophysical Journal, 2014

Complex organic molecules (COMs) have been detected in a variety of environments, including cold prestellar cores. Given the low temperature of these objects, these last detections challenge existing models. We report here new observations towards the prestellar core L1544. They are based on an unbiased spectral survey of the 3mm band at the IRAM-30m telescope, as part of the Large Program ASAI. The observations allow us to provide the full census of the oxygen bearing COMs in this source. We detected tricarbon monoxide, methanol, acetaldehyde, formic acid, ketene, and propyne with abundances varying from 5 × 10 −11 to 6 × 10 −9 . The non-LTE analysis of the methanol lines shows that they are likely emitted at the border of the core, at a radius of ∼ 8000 AU where T ∼ 10 K and n H 2 ∼ 2× 10 4 cm −3 . Previous works have shown that water vapour is enhanced in the same region because of the photodesorption of water ices. We propose that a non-thermal desorption mechanism is also responsible for the observed emission of methanol and COMs from the same layer. The desorbed oxygen and a tiny amount of desorbed methanol and ethene are enough to reproduce the abundances of tricarbon monoxide, methanol, acetaldehyde and ketene measured in L1544. These new findings open the possibility that COMs in prestellar cores originate in a similar outer layer rather than in the dense inner cores, as previously assumed, and that their formation is driven by the non-thermally desorbed species.

The Astronomy and Astrophysics Review, 2016

Recent observational and experimental evidence for the presence of complex organics in space is reviewed. Remote astronomical observations have detected ∼200 gas-phased molecules through their rotational and vibrational transitions. Many classes of organic molecules are represented in this list, including some precursors to biological molecules. A number of unidentified spectral phenomena observed in the interstellar medium are likely to have originated from complex organics. The observations of these features in distant galaxies suggests that organic synthesis had already taken place during the early epochs of the Universe. In the Solar System, almost all biologically relevant molecules can be found in the soluble component of carbonaceous meteorites. Complex organics of mixed aromatic and aliphatic structures are present in the insoluble component of meteorites. Hydrocarbons cover much of the surface of the planetary satellite Titan and complex organics are found in comets and interplanetary dust particles. The possibility that the early Solar System, or even the early Earth, have been enriched by interstellar organics is discussed.

Astrophysics and Space Science, 2009

Organic compounds of high degree of complexity are now known to be widespread in the Universe, ranging from objects in our Solar System to distant galaxies. Through the techniques of millimeter-wave spectroscopy, over 140 molecules have been identified through their rotational transitions. Space infrared spectroscopy has detected the stretching and bending modes of compounds with aromatic and aliphatic structures. Analyses of samples of meteorites, comets, asteroids, and interplanetary dust also revealed a rich content of organic substances, some of which could be of extra-solar origin. We review the current state of understanding of the origin, evolution, nature, and distribution of organic matter in space. Also discussed are a number of unexplained astronomical phenomena whose origins could be traced to organic carriers.