Interstellar ice consists of grains of

volatiles Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances. On planet Earth, the term ...

in the ice phase that form in the

interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

. Ice and dust grains form the primary material out of which the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

was formed. Grains of ice are found in the dense regions of

molecular cloud A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydroge ...

s, where new stars are formed. Temperatures in these regions can be as low as , 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 Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is ...

. Indeed, the ices are dominated by water and methanol, as well as

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...

and

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

. Frozen

formaldehyde Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...

and molecular hydrogen may also be present. Found in lower abundances are

nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix '' cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including me ...

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double b ...

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

s and

carbonyl sulfide Carbonyl sulfide is the chemical compound with the linear formula OCS. It is a colorless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl group double bonded to a sulfur atom. Carbonyl sulfide can be consi ...

. The mantles of interstellar ice grains are generally amorphous, only becoming crystalline in the presence of a star. The composition of interstellar ice can be determined through its

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

. As starlight passes through a

containing ice, molecules in the cloud absorb energy. This adsorption occurs at the characteristic frequencies of vibration of the gas and dust. Ice features in the cloud are relatively prominently in this spectra, and the composition of the ice can be determined by comparison with samples of ice materials on Earth. In the sites directly observable from Earth, around 60–70% of the interstellar ice consists of water, which displays a strong emission at 3.05 μm from stretching of the O–H bond. In September 2012, NASA scientists reported that polycyclic aromatic hydrocarbons (PAHs), subjected to interstellar medium (ISM) conditions, are transformed, through

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...

, oxygenation and

hydroxylation In chemistry, hydroxylation can refer to: *(i) most commonly, hydroxylation describes a chemical process that introduces a hydroxyl group () into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of OH groups in a ...

, to more complex organics - "a step along the path toward

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

and nucleotides, the raw materials of

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

and DNA, respectively". Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in ''interstellar ice grains'', particularly the outer regions of cold, dense clouds or the upper molecular layers of

protoplanetary disks A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...

Older than the Sun

Research published in the journal ''

Science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence ...

'' estimates that about 30–50% of the water in the

, like the water on Earth, the discs around

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

, and the

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...

s of other planets was already around even before the birth of the Sun.

Comet 67P/Churyumov–Gerasimenko

On 18 November 2014, spacecraft

Philae ; ar, فيلة; cop, ⲡⲓⲗⲁⲕ , alternate_name = , image = File:File, Asuán, Egipto, 2022-04-01, DD 93.jpg , alt = , caption = The temple of Isis from Philae at its current location on Agilkia Island in Lake Nasse ...

revealed presence of large amount of water ice on the

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

67P/Churyumov–Gerasimenko, the report stating that "the strength of the ice found under a layer of dust on the first landing site is surprisingly high". The team responsible for the MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) instrument, which hammered a probe into the comet, estimated that the comet is hard as ice. "Although the power of the hammer was gradually increased, we were not able to go deep into the surface," explained Tilman Spohn from the DLR Institute for Planetary Research, who led the research team.Philae reveals presence of large amount of water ice on the comet
/ref>

References

{{Reflist, refs= {{cite journal , author1=Allamandola, Louis J. , author2=Bernstein, Max P. , author3=Sandford, Scott A. , author4=Walker, Robert L. , title=Evolution of Interstellar Ices , journal=Space Science Reviews , volume=90 , issue=1/2 , pages=219–232 , date=October 1999 , doi=10.1023/A:1005210417396 , pmid=11543288 , bibcode=1999SSRv...90..219A , s2cid=189766820 {{cite book , author=Pirronello, Valerio , author2=Krełowski, Jacek , author3=Manicò, Giulio , author4=North Atlantic Treaty Organization. Scientific Affairs Division , title=Solid state astrochemistry , page=288 , volume=120 , series=NATO science series: Mathematics, physics, and chemistry , publisher=Springer , date=2003 , isbn=978-1-4020-1559-5 {{cite book , author=Greenberg, J. Mayo , date=1991 , chapter=Interstellar Dust-Gas Relationships , page=58 , title=Cosmic rays, supernovae, and the interstellar medium , issue=337 , series=NATO ASI series: Mathematical and physical sciences , editor1=Maurice Mandel Shapiro , editor2=Rein Silberberg , editor3=J. P. Wefel , publisher=Springer , isbn=978-0-7923-1278-9 {{citation , display-authors=1 , last1=Gibb , first1=E. L. , last2=Whittet , first2=D. C. B. , last3=Boogert , first3=A. C. A. , last4=Tielens , first4=A. G. G. M. , title=eInterstellar Ice: The Infrared Space Observatory Legacy , journal=The Astrophysical Journal Supplement Series , volume=151 , issue=1 , pages=35–73 , date=March 2004 , doi=10.1086/381182 , bibcode=2004ApJS..151...35G , doi-access=free Ice Astrochemistry Water ice

Older than the Sun

Comet 67P/Churyumov–Gerasimenko

See also

References