A PhD student in Sydney has accomplished what sounds like a very elaborate home chemistry project: producing cosmic dust from scratch by recreating a small piece of the universe inside a laboratory bottle. The experiment offers new clues about how some of the chemical ingredients associated with life could have developed before Earth even formed.
Linda Losurdo, a PhD candidate in materials and plasma physics at the University of Sydney, combined nitrogen, carbon dioxide and acetylene to simulate the energetic conditions found near stars and supernova remnants. She then exposed the gases to a powerful electrical charge. The process created carbon-rich dust resembling material that floats through interstellar space and is preserved inside comets, asteroids and meteorites. The findings were published in The Astrophysical Journal of the American Astronomical Society.
The laboratory dust contains complex combinations of carbon, hydrogen, oxygen and nitrogen - collectively known as CHON molecules - found in many organic substances considered important for life. "We no longer have to wait for an asteroid or comet to come to Earth to understand their histories," Ms. Losurdo said. "You can build analogue environments in the laboratory and reverse engineer their structure using the infrared fingerprints." She added, "It's like we have recreated a little bit of the Universe in a bottle in our lab."
In space, cosmic dust develops under extreme conditions where molecules are repeatedly struck by ions and electrons, triggering chemical reactions that create increasingly complex materials. Astronomers identify different types of cosmic dust by studying the infrared light they emit - molecular fingerprints that reveal chemical structure. Losurdo's laboratory samples produced the same distinctive infrared signatures seen in space, indicating the experiment closely reproduces real cosmic processes.
How life began on Earth remains one of science's greatest unanswered questions. Researchers investigate whether the first organic molecules formed on the young planet, arrived aboard comets and meteorites, were delivered while the solar system was still taking shape, or resulted from a combination. From about 4.56 billion to 3.5 billion years ago, meteorites, micrometeorites and interplanetary dust particles repeatedly struck Earth, carrying enormous quantities of organic material. However, where that material originally formed and which processes created it are still uncertain.
"Covalently bonded carbon and hydrogen in comet and asteroid material are believed to have formed in the outer envelopes of stars, in high-energy events like supernovae, and in interstellar environments," Ms. Losurdo said. "What we're trying to understand are the specific chemical pathways and conditions that incorporate all of the CHON elements into the complex organic structures we see in cosmic dust and meteorites."
Losurdo conducted the experiment with her supervisor, Professor David McKenzie. They first used a vacuum pump to remove air from glass tubes, producing near-space emptiness. They then filled the tubes with nitrogen, carbon dioxide and acetylene. For approximately one hour, the gas mixture was subjected to an electrical potential of around 10,000 volts, creating a glow discharge plasma. The intense energy split the original molecules apart, and their components recombined into larger, more complicated chemical structures. The newly formed material settled onto silicon chips inside the tubes, leaving behind a thin coating of dust - in some samples resembling sparkling fragments of cosmic material.
McKenzie said producing this dust on Earth gives scientists access to conditions that cannot easily be examined directly in space. "By making cosmic dust in the lab, we can explore the intensity of ion impacts and temperatures involved when dust forms in space," he said. "That's important if you want to understand the environments inside cosmic dust clouds, where life-relevant chemistry is thought to be happening. This also helps us interpret what a meteorite or asteroid fragment has been through over its lifetime."
The research could do more than clarify how life-related molecules first formed. The team plans to assemble a detailed database of infrared fingerprints produced by different types of laboratory-made cosmic dust. Astronomers could compare those signatures with observations of star-forming regions and the remains of dead stars, revealing where certain forms of dust are produced and helping reconstruct the physical and chemical processes occurring there. The database could also improve scientists' ability to interpret the history recorded inside meteorites and asteroid fragments, whose chemistry preserves evidence of temperatures, radiation and particle impacts during their journeys through space.
Losurdo received the award for best presentation for this research at the international Annual Meeting of the Meteoritical Society late last year. The authors reported no competing interests, acknowledged support from the University of Sydney node of Microscopy Australia, and received funding from the Australian Research Council.