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Have comets delivered the essential elements for life on Earth? It looks more and more like they could have. At least one comet could have, anyway: 67P / Churyumov – Gerasimenko.
A new study using data from ESA’s Rosetta mission shows that the comet contains the vital element phosphorus.
Researchers from the University of Turku in Finland conducted this research. The main author of the study is Esko Gardner, astrophysicist and software engineer. The title of the work is “Detection of solid phosphorus and fluorine in coma dust from comet 67P / Churyumov – Gerasimenko”, and it is published in the Monthly Notices of the Royal Astronomical Society.
The raw elements of life are known as CHNOPS, which stands for carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. The combinations of these six chemical elements make up the vast majority of biological molecules on Earth. Together, they make up almost 98% of the living matter on Earth.
Scientists had previously found the other five comets, so finding phosphorus might be the last piece of this puzzle.
The team of researchers discovered phosphorus and fluorine in the internal coma of comet 67P / Churyumov – Gerasimenko. They were present in solid particles collected only a few kilometers from the comet by Rosetta’s COmetary Secondary Ion Mass Analyzer (COSIMA) instrument. The particles were collected on the instrument’s target plates, which were then photographed from a distance. Individual particles were selected from the images and then measured with a mass spectrometer. This was all done from Earth before Rosetta ended her mission with a controlled crash of Comet 67P at the end of September 2016.
Phosphorus has already been found in comets. In a 1987 article, researchers reported the detection of phosphorus in the dust of Halley’s comet. But it was probably atomic phosphorus contained in an uncertain and chemically unavailable mineral.
Then in 2006, NASA’s Stardust spacecraft returned samples of comet 81P / Wild. The researchers found a single particle containing phosphorus, associated with calcium. The scientists concluded that the phosphorus was “most likely contained in an apatite particle”. He was also probably unavailable.
This new discovery is different: this time, the researchers found phosphorous ions in solid particles in minerals or metallic phosphorus.
“We have shown that apatite minerals are not the source of phosphorus, which implies that the phosphorus discovered is in a more reduced and possibly more soluble form,” said project manager Harry Lehto of the Department. of Physics and Astronomy from the University of Turku. .
The press release accompanying the research states that “this is the first time that CHNOPS elements necessary for life have been found in solid cometary matter. The new discovery is important for understanding how life was born on Earth. Phosphorus is essential for life on Earth, but if it is enclosed in an apatite mineral, it is largely out of reach. If it is in its gaseous form, it is not suitable either.
But the newly discovered phosphorus is no longer available. As the authors write in their article, “In the process of forming life, water-soluble reactive phosphorus compounds were required to convert nucleotide precursors to
phosphorylation in active nucleotides. ”
Phosphorus is one of the missing pieces of the puzzle of life on Earth. There was a dearth of molecules containing soluble phosphorus on early Earth. Experiments have shown that soluble phosphorus could play a critical role in the origin of biological molecules. “It has been shown experimentally that soluble P, HCN and H2S can serve as suitable raw materials for the prebiotic synthesis of nucleotides, amino acids and phosphoglycerin backbones,” write the authors.
But the most efficient way to produce these biological molecules involves very reduced forms of phosphorus. These forms of phosphorus occur mainly in meteoritic materials, or perhaps in elemental phosphorus. Until now, meteorites, or perhaps geochemical processes, have been known to be responsible for the prebiotic phosphoric materials necessary for life.
But this study shows that along with CHNO and S, P is now known to be present in comets, and these comets may have delivered P to early Earth.
But there is still a problem with the idea of delivering comets. If the impact is too forceful, the materials can be destroyed or changed. The team behind this new research thinks they have an answer for this. “It is conceivable that the first cometary impacts on the planet’s surface were less energetic than the impacts of heavy stony meteorites, thus preserving the prebiotic molecules in a more intact state.
Researchers are always cautious about their results. The results show that the elements of life can come from comets, but these compounds must be soluble and available. They cannot be locked in minerals. “The solubility of cometary phosphorus detected from 67P / CG is unclear, but we can conclude that it cannot be apatite, which is a common mineral source of phosphorus in meteorites. In addition, other phosphate minerals are unlikely, as we could not find a clear cometary contribution of PO2? and PO3 ?. “
So what’s the next step?
The authors believe that a comet sample return mission is necessary to advance the idea of delivering comet CHNOPS. “The presence of all of the CHNOPS elements gives a solid premise for a future mission to return cometary samples to a comet. This could confirm the presence of all compounds and their possible mineral sources and the possible solubility of the material. It would also be
allow a complete analysis of the relative amounts of these
CHNOPS elements. “
NASA’s Stardust mission captured and returned comet dust material from the comet 81P / Wild 2. And scientists have learned a lot from these samples. But these samples, while important, suffered from certain limitations. In the report “The Comet Coma Rendezvous Sample Return Mission Concept (CCRSR) – The Next Step Beyond Stardust,” the authors noted that “these samples have important limitations, however, because they were collected in modest numbers at severe hypervelocities
and represent a single random sample of the coma (a “spot” sample). “
How could this be improved? In the same report, the authors described what an enhanced comet sample return mission would look like. “This mission uses a spacecraft designed to join a comet, make prolonged observations in the comet coma (but not land on the comet), gently collect several coma samples representing different source sites, and return them to Earth for study.”
Benefits? “First, samples will be captured at much lower speeds, thus eliminating destruction and spoilage of samples during collection, and resulting in the return of much more virgin material, especially organics.
and fragile minerals. This enhanced mission would also allow the collection of samples from the coma and gaseous fowl jets. It would also allow much more data to be collected, which would make the sample more statistically relevant.
For now, this updated mission is just a concept. And there is no shortage of valid mission concepts. It is simply a matter of selecting the most worthy.
The NASA? ESA? Are you listening
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