# Tholin

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Class of molecules formed by ultraviolet irradiation of organic compounds

[Neverland Regio](/source/Neverland_Regio), a dark region on [Charon](/source/Charon_(moon))'s north pole. The region is stained a dark brown by deposits of tholins

**Tholins** (after the Greek θολός (**tholós**) "hazy" or "muddy";[1] from the [ancient Greek](/source/Ancient_Greek) word meaning "sepia ink") are a wide variety of [organic compounds](/source/Organic_compounds) formed by solar [ultraviolet](/source/Ultraviolet) or [cosmic ray](/source/Cosmic_rays) irradiation of simple carbon-containing compounds such as [carbon dioxide](/source/Carbon_dioxide) (CO 2), [methane](/source/Methane) (CH 4) or [ethane](/source/Ethane) (C 2H 6), often in combination with [nitrogen](/source/Nitrogen) (N 2) or [water](/source/Water) (H 2O).[2][3] Tholins are disordered [polymer](/source/Polymer)-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically [nitriles](/source/Nitrile) and [hydrocarbons](/source/Hydrocarbon), and their degraded forms such as [amines](/source/Amine) and [phenyls](/source/Phenyl_group). Tholins do not form naturally on modern-day [Earth](/source/Earth), but they are found in great abundance on the surfaces of icy bodies in the outer [Solar System](/source/Solar_System), and as reddish [aerosols](/source/Aerosol) in the atmospheres of outer Solar System planets and moons.

In the presence of water, tholins could be raw materials for prebiotic chemistry (i.e., the non-living chemistry that forms the basic chemicals of which life is made). Their existence has implications for the [origins of life](/source/Abiogenesis) on Earth and possibly on other planets. As particles in an atmosphere, tholins scatter light, and can affect [habitability](/source/Planetary_habitability).

Tholins may be produced in a laboratory, and are usually studied as a heterogeneous mixture of many chemicals with many different structures and properties. Using techniques like [thermogravimetric analysis](/source/Thermogravimetric_analysis), [astrochemists](/source/Astrochemistry) analyze the composition of these tholin mixtures, and the exact character of the individual chemicals within them.[4]

## Overview

[Polyacrylonitrile](/source/Polyacrylonitrile), one hypothesized polymeric component of tholins, mostly in chemically degraded form as polymers containing [nitrile](/source/Cyanide) and [amino](/source/Amine) groups. It is used experimentally to create tholin mixtures.[4]

The term "tholin" was coined by astronomer [Carl Sagan](/source/Carl_Sagan) and his colleague [Bishun Khare](/source/Bishun_Khare) to describe the difficult-to-characterize substances they obtained in his [Miller–Urey-type experiments](/source/Miller%E2%80%93Urey_experiment) on the methane-containing gas mixtures such as those found in [Titan](/source/Titan_(moon))'s atmosphere.[1] Their paper proposing the name "tholin" said:

For the past decade we have been producing in our laboratory a variety of complex organic solids from mixtures of the cosmically abundant gases CH 4, C 2H 6, NH 3, H 2O, HCHO, and H 2S. The product, synthesized by ultraviolet (UV) light or spark discharge, is a brown, sometimes sticky, residue, which has been called, because of its resistance to conventional analytical chemistry, "intractable polymer". [...] We propose, as a model-free descriptive term, 'tholins' (Greek Θολός, muddy; but also Θόλος, vault or dome), although we were tempted by the phrase 'star-tar'.[3][1]

Tholins are not one specific compound but rather are descriptive of a spectrum of molecules, including [heteropolymers](/source/Heteropolymer),[5][6] that give a reddish, organic surface covering on certain planetary surfaces. Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups.[7] Sagan and Khare note "The properties of tholins will depend on the energy source used and the initial abundances of precursors, but a general physical and chemical similarity among the various tholins is evident."[1]

Some researchers in the field prefer a narrowed definition of tholins, for example S. Hörst wrote: "Personally, I try to use the word 'tholins' only when describing the laboratory-produced samples, in part because we do not really know yet how similar the material we produce in the lab is to the material found on places like Titan or Triton (or Pluto!)."[3] French researchers also use the term tholins only when describing the laboratory-produced samples as analogues.[8] NASA scientists also prefer the word 'tholin' for the products of laboratory simulations, and use the term 'refractory residues' for actual observations on astronomical bodies.[7]

## Formation

The formation of tholins in the [atmosphere of Titan](/source/Atmosphere_of_Titan)

### Artificially

The key elements of tholins are carbon, nitrogen, and hydrogen. Laboratory infrared spectroscopy analysis of experimentally synthesized tholins has confirmed earlier identifications of chemical groups present, including primary [amines](/source/Amine), [nitriles](/source/Nitrile), and [alkyl](/source/Alkyl) portions such as CH 2/CH 3 forming complex disordered macromolecular solids. Laboratory tests generated complex solids formed from exposure of N 2:CH 4 gaseous mixtures to electrical discharge in cold plasma conditions, reminiscent of the famous [Miller–Urey experiment](/source/Miller%E2%80%93Urey_experiment) conducted in 1952.[9]

### Naturally

As illustrated to the right, tholins are thought to form in nature through a chain of chemical reactions known as [pyrolysis](/source/Pyrolysis) and [radiolysis](/source/Radiolysis). This begins with the [dissociation](/source/Dissociation_(chemistry)) and [ionization](/source/Ionization) of molecular [nitrogen](/source/Nitrogen) (N 2) and [methane](/source/Methane) (CH 4) by energetic particles and solar radiation. This is followed by the formation of [ethylene](/source/Ethylene), [ethane](/source/Ethane), [acetylene](/source/Acetylene), [hydrogen cyanide](/source/Hydrogen_cyanide), and other small simple molecules and small positive ions. Further reactions form [benzene](/source/Benzene) and other organic molecules, and their polymerization leads to the formation of an aerosol of heavier molecules, which then condense and precipitate on the planetary surface below.[10]

Tholins formed at low pressure tend to contain nitrogen atoms in the interior of their molecules, while tholins formed at high pressure are more likely to have nitrogen atoms located in terminal positions.[11][12]

Tholins may be a major constituent of the [interstellar medium](/source/Interstellar_medium).[1] On Titan, their chemistry is initiated at high altitudes and participates in the formation of solid organic particles.[8]

These atmospherically derived substances are distinct from *ice tholin II*, which are formed instead by irradiation ([radiolysis](/source/Radiolysis)) of [clathrates](/source/Clathrate) of [water](/source/Water) and organic compounds such as methane (CH 4) or ethane (C 2H 6).[2][13] The radiation-induced synthesis on ice are independent of temperature.[2]

Models show that, even when far from UV radiation of a star, [cosmic ray](/source/Cosmic_ray) doses may be fully sufficient to convert carbon-containing ice grains entirely to complex organics in less than the lifetime of the typical [interstellar cloud](/source/Interstellar_cloud).[2]

## Biological significance

Some researchers have speculated that Earth may have been seeded by organic compounds early in its development by tholin-rich comets, providing the raw material necessary for life to develop.[1][2] (See [Miller–Urey experiment](/source/Miller%E2%80%93Urey_experiment) for discussion.) Tholins do not exist naturally on present-day Earth due to the oxidizing properties of the free oxygen component of its atmosphere ever since the [Great Oxygenation Event](/source/Great_Oxygenation_Event) around 2.4 billion years ago.[14]

Laboratory experiments[15] suggest that tholins near large pools of liquid water that might persist for thousands of years could facilitate the formation of prebiotic chemistry to take place,[16][3] and has implications for the [origins of life](/source/Abiogenesis) on Earth and possibly other planets.[3][14] Also, as particles in the atmosphere of an [exoplanet](/source/Exoplanet), tholins affect the light scatter and act as a screen for protecting planetary surfaces from [ultraviolet](/source/Ultraviolet) radiation, affecting [habitability](/source/Planetary_habitability).[3][17] Laboratory simulations found derived residues related to [amino acids](/source/Amino_acid) as well as [urea](/source/Urea), with important [astrobiological](/source/Astrobiology) implications.[14][15][18]

On Earth, a wide variety of [soil bacteria](/source/Soil_biology) are able to use laboratory-produced tholins as their sole source of carbon. Tholins could have been the first microbial food for [heterotrophic](/source/Heterotroph) microorganisms before [autotrophy](/source/Autotroph) evolved.[19][20]

## Occurrence

The surface of Titan as viewed from the [*Huygens* lander](/source/Huygens_(spacecraft)). Tholins are suspected to be the source of the reddish color of both the surface and the atmospheric haze.

Sagan and Khare note the presence of tholins through multiple locations: "as a constituent of the Earth's primitive oceans and therefore relevant to the [origin of life](/source/Origin_of_life); as a component of red aerosols in the atmospheres of the outer planets and Titan; present in [comets](/source/Comet), carbonaceous chondrites asteroids, and pre-planetary solar nebulae; and as a major constituent of the [interstellar medium](/source/Interstellar_medium)."[1] The surfaces of comets, [centaurs](/source/Centaur_(planetoid)), and many icy moons and [Kuiper-belt](/source/Kuiper_belt) objects in the outer Solar System are rich in deposits of tholins.[21]

### Moons

#### Titan

[Titan](/source/Titan_(moon)) tholins are nitrogen-rich[22][23] organic substances produced by the irradiation of the gaseous mixtures of nitrogen and methane found in the atmosphere and surface of Titan. Titan's atmosphere is about 97% nitrogen, 2.7±0.1% methane and the remaining trace amounts of other gases.[24] In the case of Titan, the haze and orange-red color of its atmosphere are both thought to be caused by the presence of tholins.[10][25]

#### Europa

Linear fractures on Europa's surface, likely colored by tholins.

Colored regions on Jupiter's satellite [Europa](/source/Europa_(moon)) are thought to be tholins.[16][26][27][28] The morphology of Europa's impact craters and ridges is suggestive of fluidized material welling up from the fractures where [pyrolysis](/source/Pyrolysis) and [radiolysis](/source/Radiolysis) take place. In order to generate colored tholins on Europa there must be a source of materials (carbon, nitrogen, and water), and a source of energy to drive the reactions. Impurities in the water ice crust of Europa are presumed both to emerge from the interior as [cryovolcanic](/source/Cryovolcano) events that resurface the body, and to accumulate from space as interplanetary dust.[16]

#### Rhea

The trailing hemisphere of Saturn's moon [Rhea](/source/Rhea_(moon)) is covered with tholins.

Close-up view of Sputnik Planitia on Pluto as viewed by the *[New Horizons](/source/New_Horizons)* spacecraft, showing nitrogen ice glaciers and reddish-colored tholins.

The extensive dark areas on the trailing hemisphere of Saturn's moon [Rhea](/source/Rhea_(moon)) are thought to be deposited tholins.[13]

#### Triton

Neptune's moon [Triton](/source/Triton_(moon)) is observed to have the reddish color characteristic of tholins.[22] Triton's atmosphere is mostly nitrogen, with trace amounts of methane and carbon monoxide.[29][30]

### Dwarf planets

#### Pluto

Tholins occur on the [dwarf planet](/source/Dwarf_planet) [Pluto](/source/Pluto)[31] and are responsible for red colors[32] as well as the blue tint of the [atmosphere of Pluto](/source/Atmosphere_of_Pluto).[33] The reddish-brown cap of the north pole of [Charon](/source/Charon_(moon)),[3] the largest of five [moons of Pluto](/source/Moons_of_Pluto), is thought to be composed of tholins, produced from methane, nitrogen and related gases released from the atmosphere of Pluto and transferred over about 19,000 km (12,000 mi) distance to the orbiting moon.[34][35][36]

#### Ceres

Tholins were detected on the dwarf planet [Ceres](/source/Ceres_(dwarf_planet)#Carbon) by the [*Dawn* mission](/source/Dawn_(spacecraft)).[37][38] Most of the planet's surface is extremely rich in carbon, with approximately 20% carbon by mass in its near surface.[39][40] The carbon content is more than five times higher than in [carbonaceous chondrite](/source/Carbonaceous_chondrite) meteorites analyzed on Earth.[40]

#### Makemake

[Makemake](/source/Makemake) exhibits [methane](/source/Methane), large amounts of [ethane](/source/Ethane) and tholins, as well as smaller amounts of [ethylene](/source/Ethylene), [acetylene](/source/Acetylene) and high-mass [alkanes](/source/Alkane) may be present, most likely created by [photolysis](/source/Photolysis) of methane by solar radiation.[41][42][43]

### Kuiper belt objects and Centaurs

The reddish color typical of tholins is characteristic of many [trans-Neptunian objects](/source/Trans-Neptunian_object), including [plutinos](/source/Plutino) in the outer Solar System such as [28978 Ixion](/source/28978_Ixion).[44] Spectral reflectances of [centaurs](/source/Centaur_(minor_planet)) also suggest the presence of tholins on their surfaces.[45][46][47] The *New Horizons* exploration of the [classical Kuiper belt object](/source/Classical_Kuiper_belt_object) [486958 Arrokoth](/source/486958_Arrokoth) revealed reddish color at its surface, suggestive of tholins.[7][48]

### Comets and asteroids

Tholins were detected *in situ* by the [*Rosetta*](/source/Rosetta_(spacecraft)) mission to comet [67P/Churyumov–Gerasimenko](/source/67P%2FChuryumov%E2%80%93Gerasimenko).[49][50] Tholins are not typically characteristic of main-belt asteroids, but have been detected on the asteroid [24 Themis](/source/24_Themis).[51][52]

### Tholins beyond the Solar System

Tholins might have also been detected in the stellar system of the young star [HR 4796A](/source/HR_4796) using the [Near-Infrared Camera and Multi-Object Spectrometer (NICMOS)](/source/NICMOS) aboard the Hubble Space Telescope.[53] The [HR 4796](/source/HR_4796) system is approximately 220 light years from Earth.[54]

## See also

- [Abiogenesis](/source/Abiogenesis) – Life arising from non-living matter

- [Asphaltene](/source/Asphaltene) – Heavy organic molecular substances that are found in crude oil

- [Hemolithin](/source/Hemolithin) – Protein claimed to be of extraterrestrial origin

- [Kerogen](/source/Kerogen) – Solid organic matter in sedimentary rocks

- [PAH world hypothesis](/source/PAH_world_hypothesis) – Hypothesis about the origin of life

- [Pseudo-panspermia](/source/Pseudo-panspermia) – Supported hypothesis for the origin of life

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1. **[^](#cite_ref-21)** Poch, Olivier; Pommerol, Antoine; Jost, Bernhard; Carrasco, Nathalie; Szopa, Cyril; Thomas, Nicolas (2016). "Sublimation of water ice mixed with silicates and tholins: Evolution of surface texture and reflectance spectra, with implications for comets". *Icarus*. **267**: 154–173. [Bibcode](/source/Bibcode_(identifier)):[2016Icar..267..154P](https://ui.adsabs.harvard.edu/abs/2016Icar..267..154P). [doi](/source/Doi_(identifier)):[10.1016/j.icarus.2015.12.017](https://doi.org/10.1016%2Fj.icarus.2015.12.017). [S2CID](/source/S2CID_(identifier)) [56028928](https://api.semanticscholar.org/CorpusID:56028928).

1. ^ [***a***](#cite_ref-McDonald1994_22-0) [***b***](#cite_ref-McDonald1994_22-1) McDonald, Gene D.; Thompson, W.Reid; Heinrich, Michael; Khare, Bishun N.; Sagan, Carl (1994). ["Chemical Investigation of Titan and Triton Tholins"](https://doi.org/10.1006%2Ficar.1994.1046). *Icarus*. **108** (1): 137–145. [Bibcode](/source/Bibcode_(identifier)):[1994Icar..108..137M](https://ui.adsabs.harvard.edu/abs/1994Icar..108..137M). [doi](/source/Doi_(identifier)):[10.1006/icar.1994.1046](https://doi.org/10.1006%2Ficar.1994.1046). [PMID](/source/PMID_(identifier)) [11539478](https://pubmed.ncbi.nlm.nih.gov/11539478).

1. **[^](#cite_ref-23)** Derenne, S.; Coelho, C.; Anquetil, C.; Szopa, C.; Rahman, A.S.; McMillan, P.F.; Corà, F.; Pickard, C.J.; Quirico, E.; Bonhomme, C. (2012). ["New insights into the structure and chemistry of Titan's tholins via 13C and 15N solid state nuclear magnetic resonance spectroscopy"](http://discovery.ucl.ac.uk/1377547/2/1377547.pdf) (PDF). *Icarus*. **221** (2): 844–853. [Bibcode](/source/Bibcode_(identifier)):[2012Icar..221..844D](https://ui.adsabs.harvard.edu/abs/2012Icar..221..844D). [doi](/source/Doi_(identifier)):[10.1016/j.icarus.2012.03.003](https://doi.org/10.1016%2Fj.icarus.2012.03.003).

1. **[^](#cite_ref-24)** Coustenis, Athena; Taylor, Frederic W. (2008). [*Titan: Exploring an Earthlike World*](https://archive.org/details/titanexploringea00cous). World Scientific. pp. [154](https://archive.org/details/titanexploringea00cous/page/n172)–155. [ISBN](/source/ISBN_(identifier)) [978-981-270-501-3](https://en.wikipedia.org/wiki/Special:BookSources/978-981-270-501-3).

1. **[^](#cite_ref-25)** ["Task 3.4 Tholin Chemical Analysis"](https://astrobiology.nasa.gov/nai/annual-reports/2010/jpl-titan/task-34-tholin-chemical-analysis/). *NASA Astrobiology Institute*. August 2010.

1. **[^](#cite_ref-amino_acids_26-0)** Whalen, Kelly; Lunine, Jonathan I.; [Blaney, Diana L.](/source/Diana_Blaney) (2017). "MISE: A Search for Organics on Europa". *American Astronomical Society Meeting Abstracts*. **229**: 138.04. [Bibcode](/source/Bibcode_(identifier)):[2017AAS...22913804W](https://ui.adsabs.harvard.edu/abs/2017AAS...22913804W).

1. **[^](#cite_ref-JPL2015_27-0)** ["Europa Mission to Probe Magnetic Field and Chemistry"](https://www.jpl.nasa.gov/news/news.php?feature=4602). *Jet Propulsion Laboratory*. 27 May 2015. Retrieved 2017-10-23.

1. **[^](#cite_ref-28)** Khare, B. N.; Nna Mvondo, D.; Borucki, J. G.; Cruikshank, D. P.; Belisle, W. A.; Wilhite, P.; McKay, C. P. (2005). "Impact Driven Chemistry on Europa's Surface". *Bulletin of the American Astronomical Society*. **37**: 753. [Bibcode](/source/Bibcode_(identifier)):[2005DPS....37.5810K](https://ui.adsabs.harvard.edu/abs/2005DPS....37.5810K).

1. **[^](#cite_ref-29)** [Neptune's Moon Triton](https://www.universetoday.com/56042/triton/). Matt Williams, *Universe Today*. 16 October 2016.

1. **[^](#cite_ref-30)** ["Triton"](https://science.nasa.gov/neptune/moons/triton/). *NASA Science*. 21 November 2017. Retrieved 14 November 2023.

1. **[^](#cite_ref-31)** ["Pluto: The 'Other' Red Planet"](https://www.nasa.gov/nh/pluto-the-other-red-planet). *NASA*. 3 July 2015. Retrieved 2015-07-06. Experts have long thought that reddish substances are generated as a particular color of ultraviolet light from the sun, called Lyman-alpha, strikes molecules of the gas methane (CH 4) in Pluto's atmosphere, powering chemical reactions that create complex compounds called tholins.

1. **[^](#cite_ref-32)** ["NASA released an incredibly detailed photo of snow - and something else - on Pluto"](http://www.businessinsider.com/nasa-released-an-incredibly-detailed-photo-of-snow-and-something-else-on-pluto-2016-3), *Business Insider Australia,* Mar. 6, 2016 (accessed 28 Feb. 2018).

1. **[^](#cite_ref-33)** Amos, Jonathan (8 October 2015). ["New Horizons: Probe captures Pluto's blue hazes"](https://www.bbc.com/news/science-environment-34481347). *BBC News*.

1. **[^](#cite_ref-NASA-20150909_34-0)** Albert, P.T. (9 September 2015). ["New Horizons Probes the Mystery of Charon's Red Pole"](https://blogs.nasa.gov/pluto/2015/09/09/new-horizons-probes-the-mystery-of-charons-red-pole/). *[NASA](/source/NASA)*. Retrieved 2015-09-09.

1. **[^](#cite_ref-NYT-20160914_35-0)** Bromwich, Jonah Engel; St. Fleur, Nicholas (14 September 2016). ["Why Pluto's Moon Charon Wears a Red Cap"](https://www.nytimes.com/2016/09/15/science/pluto-moon-charon.html). *[New York Times](/source/New_York_Times)*. Retrieved 14 September 2016.

1. **[^](#cite_ref-36)** H. S. Shi; I. L. Lai; W. H. Ip (2019). [*The Long-Term Evolution of Pluto's Atmosphere and Its Effect on Charon's Surface Tholin Formation*](https://www.hou.usra.edu/meetings/plutosystem2019/pdf/7014.pdf) (PDF). Pluto System After New Horizons 2019 (LPI Contrib. No. 2133).

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1. **[^](#cite_ref-PO_12_2018_39-0)** [Team finds evidence for carbon-rich surface on Ceres](https://phys.org/news/2018-12-team-evidence-carbon-rich-surface-ceres.html). Southwest Research Institute. Published by *PhysOrg*. 10 December 2018.

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1. **[^](#cite_ref-47)** Szabó, Gy. M.; Kiss; et al. (2018). ["Surface Ice and Tholins on the Extreme Centaur 2012 DR30"](https://doi.org/10.3847%2F1538-3881%2Faab14e). *The Astronomical Journal*. **155** (4): 170. [Bibcode](/source/Bibcode_(identifier)):[2018AJ....155..170S](https://ui.adsabs.harvard.edu/abs/2018AJ....155..170S). [doi](/source/Doi_(identifier)):[10.3847/1538-3881/aab14e](https://doi.org/10.3847%2F1538-3881%2Faab14e).

1. **[^](#cite_ref-48)** [NASA to Make Historic New Year's Day Flyby of Mysterious Ultima Thule. Here's What to Expect.](https://www.space.com/42864-new-horizons-ultima-thule-flyby-what-to-expect.html) Nola Taylor Redd, *Space.com*. 31 December 2018.

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v t e Molecules detected in outer space Molecules Diatomic Aluminium monochloride Aluminium monofluoride Aluminium(II) oxide Argonium Carbon cation Carbon monophosphide Carbon monosulfide Carbon monoxide Cyano radical Diatomic carbon Fluoromethylidynium Helium hydride ion Hydrogen chloride Hydrogen fluoride Hydrogen (molecular) Hydroxyl radical Imidogen Iron(II) oxide Magnesium monohydride Methylidyne radical Nitric oxide Nitrogen (molecular) Oxygen (molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfanyl Sulfur mononitride Sulfur monoxide Titanium(II) oxide Triatomic Aluminium(I) hydroxide Aluminium isocyanide Amino radical Carbon dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen cyanide (HCN) Hydrogen isocyanide (HNC) Hydrogen sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene Methylidynephosphane N2H+ Nitrous oxide Nitroxyl Ozone Potassium cyanide Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide SiNC Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Trihydrogen cation Water Four atoms Acetylene Ammonia Cyanoethynyl Formaldehyde Fulminic acid HCCN Hydrogen peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methyl cation Methyl radical Methylene amidogen Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thiocyanic acid Thioformaldehyde Tricarbon monosulfide Tricarbon monoxide Five atoms Ammonium ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy radical Methylenimine Propadienylidene Protonated formaldehyde Silane Silicon-carbide cluster Six atoms Acetonitrile Cyanobutadiynyl radical Cyclopropenone Diacetylene E-Cyanomethanimine Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene Seven atoms Acetaldehyde Acrylonitrile Vinyl cyanide Cyanodiacetylene Ethylene oxide Glycolonitrile Hexatriynyl radical Methyl isocyanate Methylamine Propyne Vinyl alcohol Eight atoms Acetic acid Acrolein Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Hexapentaenylidene Methyl formate Methylcyanoacetylene Nine atoms Acetamide Cyanohexatriyne Dimethyl ether Ethanethiol Ethanol Methyldiacetylene N-Methylformamide Octatetraynyl radical Propene Propionitrile Ten atoms or more Acetone Benzene Benzonitrile Buckminsterfullerene (C60, C60+, fullerene, buckyball) Butyronitrile C70 fullerene Cyanodecapentayne Cyclopentindene Ethyl formate Ethylene glycol Heptatrienyl radical Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propionaldehyde Pyrimidine Deuterated molecules Ammonia Ammonium ion Formaldehyde Formyl radical Heavy water Hydrogen cyanide Hydrogen deuteride Hydrogen isocyanide N2D+ Propyne Trihydrogen cation Unconfirmed Anthracene Dihydroxyacetone Glycine Graphene H2NCO+ Hemolithin Linear C5 Methoxyethane Naphthalene cation Phosphine Pyrene Silylidyne Related Abiogenesis Astrobiology Astrochemistry Atomic and molecular astrophysics Chemical formula Circumstellar dust Circumstellar envelope Cosmic dust Cosmic ray Cosmochemistry Diffuse interstellar band Earliest known life forms Extraterrestrial life Extraterrestrial liquid water Forbidden mechanism Homochirality Intergalactic dust Interplanetary medium Interstellar medium Iron–sulfur world theory Kerogen Molecules in stars Nexus for Exoplanet System Science Organic compound Outer space PAH world hypothesis Photodissociation region Polycyclic aromatic hydrocarbon (PAH) Pseudo-panspermia RNA world hypothesis Spectroscopy Tholin Category:Astrochemistry Outer space portal Astronomy portal Chemistry portal

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- [Stars](https://en.wikipedia.org/wiki/Portal:Stars)
- [Outer space](https://en.wikipedia.org/wiki/Portal:Outer_space)
- [Solar System](https://en.wikipedia.org/wiki/Portal:Solar_System)
- [Science](https://en.wikipedia.org/wiki/Portal:Science)

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Adapted from the Wikipedia article [Tholin](https://en.wikipedia.org/wiki/Tholin) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Tholin?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.