Molecules in Space

About 350 molecules have been found between the stars, and about half of them are organic

The gas between the stars is not just atoms. In cold, dense clouds, shielded from starlight by dust, atoms meet on the surfaces of dust grains and in the gas and build molecules. The Cologne Database for Molecular Spectroscopy, which keeps the standard census, listed 346 molecules found in interstellar clouds or in the gas thrown off by old stars as of April 2026, and recommends saying "about 350". Another 74 have been found in other galaxies. Almost all were identified by radio telescopes, which pick up the precise frequencies at which each kind of molecule spins.

About half of the known interstellar molecules are complex organic molecules: carbon compounds with six or more atoms, such as methanol, ethanol and methyl formate. They are richest in hot cores, the warm gas around newborn massive stars, such as Sagittarius B2 near the center of the Milky Way. Most molecules in space are small, though. Molecular hydrogen far outnumbers everything else, and carbon monoxide comes second; because cold hydrogen gives off almost no light, astronomers map molecular clouds by the glow of carbon monoxide instead.

These are landmark detections, by the year each molecule was first found in space:

Glycine, the simplest amino acid, has been reported in interstellar clouds but never confirmed; the census lists it as not yet detected there. It has been found in comets.

In the coldest clouds, most molecules are frozen onto dust grains as ice

At 10 to 20 degrees above absolute zero, molecules that hit a dust grain stick. The grains grow coats of ice, mostly water, with carbon monoxide, carbon dioxide, methane and ammonia. In 2023 the James Webb Space Telescope's Ice Age program measured these ices deep inside the Chamaeleon I cloud, about 630 light-years away, by the starlight they absorb from stars behind the cloud. It found water, carbon monoxide, carbon dioxide, methane, ammonia, carbonyl sulfide and methanol, with signs of larger organics such as ethanol or acetaldehyde, all before any star had formed there. Ice like this is what the planets and comets of a new solar system are built from, so they start out with a stock of organic chemistry.

Comets carry the cloud's ice, with glycine and phosphorus

Comets are ice and dust left over from the solar system's birth. The European Space Agency's Rosetta spacecraft, which orbited Comet 67P/Churyumov-Gerasimenko from 2014 to 2016, sniffed its escaping gas with the ROSINA mass spectrometer. In 2016 the team reported glycine, along with methylamine and ethylamine, molecules that can lead to it, and phosphorus, an element of DNA, cell membranes and the energy molecule ATP. Glycine had been found before in dust from Comet Wild 2, returned by NASA's Stardust mission in 2006, but those samples had landed in the Utah desert. Glycine is the one amino acid known to form without liquid water, in ice, so a comet can carry it straight from its parent cloud.

Asteroid samples hold amino acids, all five nucleobases and the sugars of RNA

Carbon-rich asteroids were once warm and wet inside, and that water turned simple ices into much larger molecules. Meteorites that fall to Earth have shown this for decades. The Murchison meteorite, which fell in Australia in 1969, contains more than 80 amino acids, most of them unknown in life on Earth. But a meteorite sits in air and soil before anyone finds it, so contamination can never be ruled out. Samples collected in space and sealed settle that.

• Ryugu (Japan, Hayabusa2): 5.4 grams returned in December 2020. Uracil, one of the bases of RNA, was found in 2023; in March 2026 a Japanese team reported all five nucleobases used in DNA and RNA (adenine, guanine, cytosine, thymine and uracil), with vitamin B3 and urea.
• Bennu (United States, OSIRIS-REx): 121.6 grams returned in September 2023. In January 2025 NASA-led teams reported 14 of the 20 amino acids life uses to build proteins, 19 that life does not use, all five nucleobases, abundant ammonia, formaldehyde and about 10,000 nitrogen-bearing compounds, plus salts left by evaporating brine. In December 2025 a Japanese-led team reported the sugars ribose, the backbone of RNA, and glucose, the first time glucose has been found in an extraterrestrial sample. There was no deoxyribose, the sugar of DNA.
• Kamoʻoalewa (China, Tianwen-2): launched in May 2025, Tianwen-2 reached this small near-Earth asteroid, which may be a fragment of the Moon, in mid-2026. Its sample capsule is due back at Earth in late 2027, and the spacecraft will go on to the main-belt comet 311P/PANSTARRS, arriving in 2035.

None of this is evidence of life. The amino acids in Bennu are left- and right-handed in equal amounts, where life uses only the left-handed forms, and every compound found can form without biology. What the samples show is that the building blocks of RNA and proteins formed widely in the early solar system and were delivered to the young Earth.

Icy moons have oceans with salts and organics, and Titan has lakes of methane

• Enceladus: Saturn's small moon sprays water from a global ocean through cracks near its south pole. Flying through the plume, NASA's Cassini spacecraft found salts, molecular hydrogen, a likely sign of hot water reacting with rock on the ocean floor, and organic molecules. In 2023 a team found sodium phosphates in the ice grains, implying phosphorus levels at least 100 times those of Earth's oceans. In 2025, reanalyzing grains caught minutes after they left the ocean, another team found esters, ethers and other organics in them.
• Titan: Saturn's largest moon has a thick nitrogen atmosphere in which sunlight turns methane into larger organic molecules, which settle out as haze and drift as dunes. Its lakes and seas are liquid methane and ethane. NASA's Dragonfly rotorcraft is due to launch in July 2028 and reach Titan in 2034 to sample them.
• Europa: in 2023 the James Webb Space Telescope found carbon dioxide on Jupiter's moon Europa, concentrated in young terrain, likely from the ocean below. NASA's Europa Clipper reaches Jupiter in 2030.
• The Moon: water ice lies in permanently shadowed craters at the poles. China's Chang'e-5, which returned 1,731 grams from the near side in 2020, brought back a hydrated mineral, (NH₄)MgCl₃·6H₂O, that is 41% water by mass, with ammonium holding the water in place at a latitude where ice cannot survive. Chang'e-6 returned 1,935.3 grams from the far side in 2024, the first far-side samples; its basalts show the far-side mantle holds only 1 to 1.5 micrograms of water per gram, the driest lunar mantle yet measured. Chang'e-7 is built to make the first direct measurements of the ice in the south polar craters.

Telescopes now read the molecules in the air of planets around other stars

When a planet passes in front of its star, starlight filters through its atmosphere, and each molecule absorbs its own wavelengths. In 2022 the James Webb Space Telescope made the first clear detection of carbon dioxide in an exoplanet atmosphere, on the hot gas giant WASP-39b, and found sulfur dioxide there made by starlight-driven chemistry, the first photochemistry seen on an exoplanet. Water, methane and carbon monoxide have since been measured on many worlds. Claims of molecules that only life makes are a different matter: a 2025 report of dimethyl sulfide on the planet K2-18b has been challenged by independent reanalyses that find no strong evidence for it.

Water is the molecule that matters most for industry in space

Every kilogram launched from Earth is expensive, so the molecules already in space are a resource. Water is the most useful: astronauts can drink it, and split by electricity it gives hydrogen and oxygen for rocket propellant and air. That is why the lunar south pole, with its ice, is the target of China's International Lunar Research Station and NASA's Artemis program. On Mars, the atmosphere is about 95% carbon dioxide. The MOXIE experiment on NASA's Perseverance rover split it into oxygen and carbon monoxide 16 times between 2021 and 2023, making 122 grams of oxygen at up to 12 grams an hour, twice its goal. Combining Martian carbon dioxide with hydrogen from water ice gives methane and oxygen, the propellants of SpaceX's Starship. Carbon-rich asteroids like Ryugu and Bennu hold water bound in clay minerals, along with carbon and nitrogen. See SolarSystemOS for the industry being built on these resources, and the periodic elements for the elements themselves.

Sources

• Cologne Database for Molecular Spectroscopy, Molecules in Space, H. S. P. Müller, University of Cologne (April 2026 count).
• Jiménez-Serra, I., Codella, C. and Belloche, A. (2025), Observations of complex organic molecules in the gas phase of the interstellar medium, arXiv:2503.17104.
• McClure, M. K. et al. (2023), An Ice Age JWST inventory of dense molecular cloud ices, Nature Astronomy 7, 431.
• Altwegg, K. et al. (2016), Prebiotic chemicals, amino acid and phosphorus, in the coma of comet 67P/Churyumov-Gerasimenko, Science Advances 2, e1600285.
• Glavin, D. P. et al. (2025), Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu, Nature Astronomy 9, 199; McCoy, T. J. et al. (2025), An evaporite sequence from ancient brine recorded in Bennu samples, Nature 637, 1072.
• Furukawa, Y. et al. (2025), Bio-essential sugars in samples from asteroid Bennu, Nature Geoscience.
• Koga, T. et al. (2026), A complete set of canonical nucleobases in the carbonaceous asteroid (162173) Ryugu, Nature Astronomy.
• Postberg, F. et al. (2023), Detection of phosphates originating from Enceladus's ocean, Nature 618, 489; Khawaja, N. et al. (2025), Detection of organic compounds in freshly ejected ice grains from Enceladus's ocean, Nature Astronomy.
• Jin, S. et al. (2024), Evidence of a hydrated mineral enriched in water and ammonium molecules in the Chang'e-5 lunar sample, Nature Astronomy; Chang'e-6 sample papers, Nature 643 (10 July 2025).
• NASA, MOXIE mission results (September 2023); China National Space Administration, Tianwen-2 and Chang'e-7 mission releases.