Hypothetical types of biochemistry are forms of biochemistry agreed to be scientifically viable but not proven to exist at this time. The kinds of living organisms currently known on Earth all use carbon compounds for basic structural and metabolic functions, water as a solvent, and DNA or RNA to define and control their form. If life exists on other planets or moons it may be chemically similar, though it is also possible that there are organisms with quite different chemistries – for instance, involving other classes of carbon compounds, compounds of another element, or another solvent in place of water.
The Miller–Urey experiment, or Miller experiment, was an experiment in chemical synthesis carried out in 1952 that simulated the conditions thought at the time to be present in the atmosphere of the early, prebiotic Earth. It is seen as one of the first successful experiments demonstrating the synthesis of organic compounds from inorganic constituents in an origin of life scenario. The experiment used methane (CH4), ammonia (NH3), hydrogen (H2), in ratio 2:2:1, and water (H2O). Applying an electric arc (simulating lightning) resulted in the production of amino acids.
Pyrimidine is an aromatic, heterocyclic, organic compound similar to pyridine. One of the three diazines, it has nitrogen atoms at positions 1 and 3 in the ring. The other diazines are pyrazine and pyridazine.
The RNA world is a hypothetical stage in the evolutionary history of life on Earth in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage.
Uracil is one of the four nucleotide bases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine (T). Uracil is a demethylated form of thymine.
Thymine is one of the four nucleotide bases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. In RNA, thymine is replaced by the nucleobase uracil. Thymine was first isolated in 1893 by Albrecht Kossel and Albert Neumann from calf thymus glands, hence its name.
Astrochemistry is the study of the abundance and reactions of molecules in the universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form.
Cosmochemistry 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. Given that the asteroid parent bodies of meteorites were some of the first solid material to condense from the early solar nebula, cosmochemists are generally, but not exclusively, concerned with the objects contained within the Solar System.
Tholins are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide, methane or ethane, often in combination with nitrogen or water. Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically nitriles and hydrocarbons, and their degraded forms such as amines and phenyls. Tholins do not form naturally on modern-day Earth, but they are found in great abundance on the surfaces of icy bodies in the outer Solar System, and as reddish aerosols in the atmospheres of outer Solar System planets and moons.
A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar and planar. Many are colorless. Many of them are found in coal and in oil deposits, and are also produced by the incomplete combustion of organic matter—for example, in engines and incinerators or when biomass burns in forest fires.
Cosmic dust – also called extraterrestrial dust, space dust, or star dust – is dust that occurs in outer space or has fallen onto Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 μm), such as micrometeoroids and meteoroids. Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust, and circumplanetary dust. There are several methods to obtain space dust measurement.
Atomic astrophysics is concerned with performing atomic physics calculations that will be useful to astronomers and using atomic data to interpret astronomical observations. Atomic physics plays a key role in astrophysics as astronomers' only information about a particular object comes through the light that it emits, and this light arises through atomic transitions.
Whether there is life on Titan, the largest moon of Saturn, is currently an open question and a topic of scientific assessment and research. Titan is far colder than Earth, but of all the places in the Solar System, Titan is the only place besides Earth known to have liquids in the form of rivers, lakes, and seas on its surface. Its thick atmosphere is chemically active and rich in carbon compounds. On the surface there are small and large bodies of both liquid methane and ethane, and it is likely that there is a layer of liquid water under its ice shell. Some scientists speculate that these liquid mixes may provide prebiotic chemistry for living cells different from those on Earth.
Abiogenesis is the natural process by which life arises from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single event, but a process of increasing complexity involving the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. The transition from non-life to life has never been observed experimentally, but many proposals have been made for different stages of the process.
Cyclopropenylidene, or c-C3H2, is a partially aromatic molecule belonging to a highly reactive class of organic molecules known as carbenes. On Earth, cyclopropenylidene is only seen in the laboratory due to its reactivity. However, cyclopropenylidene is found in significant concentrations in the interstellar medium (ISM) and on Saturn's moon Titan. Its C2v symmetric isomer, propadienylidene (CCCH2) is also found in the ISM, but with abundances about an order of magnitude lower. A third C2 symmetric isomer, propargylene (HCCCH), has not yet been detected in the ISM, most likely due to its low dipole moment.
Interstellar ice consists of grains of volatiles in the ice phase that form in the interstellar medium. Ice and dust grains form the primary material out of which the Solar System was formed. Grains of ice are found in the dense regions of molecular clouds, where new stars are formed. Temperatures in these regions can be as low as 10 K, allowing molecules that collide with grains to form an icy mantle. Thereafter, atoms undergo thermal motion across the surface, eventually forming bonds with other atoms. This results in the formation of water and methanol. Indeed, the ices are dominated by water and methanol, as well as ammonia, carbon monoxide and carbon dioxide. Frozen formaldehyde and molecular hydrogen may also be present. Found in lower abundances are nitriles, ketones, esters and carbonyl sulfide. The mantles of interstellar ice grains are generally amorphous, becoming crystalline only in the presence of a star.
OREOcube is an experiment designed by the European Space Agency (ESA) with the NASA that will investigate the effects of solar and cosmic radiation on selected organic compounds. It will consist in a 12-month orbital study of the effects of the outer space environment on astrobiologically relevant materials in an external exposure facility on the International Space Station (ISS).
2-Methylnaphthalene is a polycyclic aromatic hydrocarbon (PAH).
Formamide-based prebiotic chemistry is a reconstruction of the beginnings of life on Earth, assuming that formamide could accumulate in sufficiently high amounts to serve as the building block and reaction medium for the synthesis of the first biogenic molecules.
Pseudo-panspermia is a well-supported hypothesis for a stage in the origin of life. The theory first asserts that many of the small organic molecules used for life originated in space. It continues that these organic molecules were distributed to planetary surfaces, where life then emerged on Earth and perhaps on other planets. Pseudo-panspermia differs from the fringe theory of panspermia, which asserts that life arrived on Earth from distant planets.
