The universe is packed with intricate, carbon-based compounds, including organic molecules, that hold clues about life’s raw materials. Some of these compounds are found in space.
Over the past few years, robotic missions have taken samples from comets and asteroids to learn how these compounds formed and whether our planet might owe its biological chemistry to faraway dust clouds.
The findings hint that organic molecules appear in every corner of space, which suggests that our own evolution may fit into a larger cosmic narrative.
Scientists studying bits of interstellar dust, comets, and asteroids keep finding the same theme: these objects contain a variety of organic molecules.
The story began in 1986 when the European Giotto spacecraft conducted the first in-situ analysis of a comet, 1P/Halley, during its apparition (when it was visible from Earth).
It revealed an unexpected abundance of organic species in the coma, but their exact origins — whether from polymeric matter or smaller molecules — remained unclear.
The small spacecraft followed the comet for two years, capturing the dust and gas it shed. Instruments recorded dozens of molecules that contained carbon, leading scientists to look deeper for connections to the early solar system.
The Rosetta spacecraft was the first to orbit and land on a comet, namely 67P. In 2015, it detected simple organic compounds, including glycine, which is a building block of proteins. This discovery marked the first direct detection of this molecule on a comet.
By 2022, researchers analyzing high-resolution mass spectrometry data identified 44 organic compounds in just one day’s worth of Rosetta data, with some molecules weighing up to 140 Daltons (Da).
“Rosetta really changed the view,” said Dr. Nora Hänni, a chemist at the University of Bern. Soon after this, her team identified dimethyl sulfide, a gas that, on Earth, is generally produced by living organisms.
Japan’s Hayabusa2 and NASA’s OSIRIS-REx missions offered a similar look at ancient space rocks. They scooped material from asteroids Ryugu and Bennu and brought the samples back to Earth.
Early analyses suggested that both asteroids have a wide range of organics present. Scientists studying Ryugu found at least 20,000 varieties of carbon-based compounds, including 15 different amino acids.
“It’s just everything possible from which life could emerge,” said Philippe Schmitt-Kopplin, an organic geoscientist at the Technical University of Munich.
Those organic-rich rocks may date back to a time before planets fully formed. Scientists wonder if these compounds started in cold, dark clouds between stars, or if they originated in energetic zones near young suns.
“Those of us interested in searching for life have to understand how planets could acquire organics in the absence of life,” said Christopher Glein, a planetary scientist at the Southwest Research Institute.
Many experts ask whether the early Earth became habitable partly because of organic molecules that arrived from space.
“I would like to know where we come from as a planetary species,” said Karin Öberg, an astrochemist at Harvard University.
Astronomers have traced certain hefty carbon structures called polycyclic aromatic hydrocarbons (PAHs) back to about 1.5 billion years after the Big Bang.
Carbon atoms often form large, sturdy rings and chains in the outflows of dying stars.
“It’s actually not too different from combustion as we understand it here on Earth,” said Öberg, referring to the ways these molecules can build up in stellar winds.
Observations confirm that interstellar space has more than 200 carbon-containing compounds.
In molecular clouds, simple ingredients gather on cold dust grains. Once stuck together, atoms can combine to form key molecules like methane.
Over time, ultraviolet radiation and cosmic rays split molecules into radical fragments, which recombine to form something new. Experiments hint that this can produce anything from methanol to glycine
“You can build complexity without much going on in just a cold, dark cloud,” said Alice Booth, an astronomer at Harvard University.
Observations of protoplanetary disks — thick, spinning layers of dust and gas around baby stars — show that methanol and other organics survive the intense heat of stellar births.
Recent modeling suggests these compounds may grow into even more sophisticated structures when disk materials cycle between hot surface zones and cooler midplane regions.
This process could be one reason comets and asteroids wind up so chemically rich by the time they form. “Comets are, I think, the best that we can do to go back in time,” said Hänni.
When organic chemicals land on a planet, they might set the stage for the emergence of living systems. A few theories propose that meteorites or comets delivered certain amino acids or PAHs to early Earth.
Astrobiologists debate about which molecules represent a solid proof of life, and which might be possible false positives.
The presence of dimethyl sulfide from comet 67P, supports the idea that lifeless processes can make molecules that we tend to associate with living organisms.
In 2016, Rosetta concluded its mission with a controlled impact on comet 67P’s surface, which resulted in a rich legacy of data for further analysis.
Since then, scientists have connected these findings to other Solar System reservoirs of organics, such as Saturn’s ring rain and meteoritic material, revealing their shared prestellar origins.
Scientists will continue exploring these mysteries with missions like NASA’s Europa Clipper, the European Space Agency’s Juice, and a future rotorcraft bound for Saturn’s moon Titan.
Researchers hope to spot organic compounds that might give hints about oceans hiding beneath icy crusts.
Such discoveries could bring us closer to answering one of humanity’s oldest questions: are we alone in the universe?
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