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An international team of scientists studied both the water and organic content of a dust particle recovered from the surface of the near-Earth S-type asteroid 25143 Itokawa by JAXA’s Hayabusa mission, which was the first mission that brought pristine asteroid material to Earth.
The S-type asteroid Itokawa. Image credit: JAXA.
“Understanding the early chemical reactions involving liquid water provides crucial information on how simple building blocks of organic compounds evolved into increasingly complex macromolecules through the actions of water,” said the author. Principal, Dr Queenie Chan, of the Department of Earth Sciences at Royal Holloway and colleagues.
“Such an investigation requires the availability of pristine samples of astromaterials – samples that have not been compromised by earth contamination, and thus preserve the intrinsic states of the physical, chemical, organic and other properties of the materials.”
“Studying the freshly collected and carefully preserved astromaterials returned from spacecraft reduces the ambiguity of the terrestrial exposure that meteorite samples have typically experienced.”
In 2010, the Hayabusa mission successfully recovered thousands of regolith particles, with sizes ranging from 10 to 200 μm, from the near-Earth asteroid Itokawa.
“Itokawa is believed to be a rubble-heaped asteroid that has been reaccreted from material from a once-large, thermally-metamorphosed, collision-disturbed precursor planetesimal,” the researchers said.
“S-type asteroids are among the most common objects in the inner asteroid belt, where the majority of Earth’s meteorites – ordinary chondrites – originate.
“Ordinary chondrites generally have a low organic content. As a result, their organic analyzes had been difficult, which is even more so in the case of returned samples of minute size and small total mass recovered. “
The chemical distribution and mineralogy of the Amazon particle of the S-type asteroid Itokawa: (A) Image showing Amazon being picked up using a glass needle with platinum threads at JAXA; (B) photomicrograph taken in visible light from Amazonia before and after being mounted in indium; (C) EDX Mg-Si-Al (Mg is red, Si is blue, Al is green) combined x-ray cards from Amazon, the grids are 10 µm in size; the locations of the EDX spectra in (E) are indicated in points 1 to 3, and (D) the Raman map of the Amazon showing the mineralogical distribution of olivine (green), plagioclase (blue), pyroxene (red) and OM (yellow); the locations of primitive OM (p-OM) and mature OM (m-OM) are marked by annotations in italics, NanoSIMS point analyzes of albite (Ab), olivine (Ol) and pyroxene (Py) are marked as open squares, and the NanoSIMS imaging analysis area is marked with a dotted square; (E) EDX spectra of olivine, pyroxene and albite, the locations of the points are indicated in (C); and (F) selected Raman spectra of mineral and organic components in the Amazon; the positions of the peaks of their characteristic Raman modes are represented by the dotted lines in their corresponding colors; (G) selected Raman spectra of Amazon olivine versus LL5 Alta-ameem heated chondrite; (H) Selected Raman spectra of organics from the Amazon compared to those of primitive and heated chondrites. Image Credit: Chan et al., doi: 10.1038 / s41598-021-84517-x.
In the study, Dr Chan and his co-authors analyzed a single grain – dubbed “ Amazon ”, to recognize its unique shape resembling the South American continent preserved after light pressure in indium – recovered from Itokawa.
Using energy dispersive x-ray spectroscopy (EDX) and Raman analysis, they detected both primitive (unheated) and processed (heated) organic matter – presented both as graphite nanocrystalline and polyaromatic carbon – less than ten microns away.
Their results suggest that Itokawa has been constantly evolving for billions of years by incorporating extraterrestrial water and organic matter.
In the past, the asteroid will have experienced extreme heating, dehydration and bursting due to a catastrophic impact.
However, despite this, Itokawa came back together from the shattered fragments and rehydrated with water which was provided by falling dust or carbon-rich meteorites.
“The organic material that was heated indicates that the asteroid had been heated to over 600 degrees Celsius in the past,” Dr Chan said.
“The presence of unheated organic matter very close to it, means that the fall of the primitive organic matter arrived at the surface of Itokawa after the cooling of the asteroid.”
The results also show that S-type asteroids, where most of Earth’s meteorites come from, like Itokawa, contain the raw ingredients of life.
Analysis of this asteroid changes traditional views of the origin of life on Earth that previously focused heavily on carbon-rich Type C asteroids.
“The ‘Amazon’ study gave us a better understanding of how the asteroid has constantly evolved by incorporating newly arrived exogenous water and organic compounds,” said Dr Chan.
“These findings are truly exciting because they reveal intricate details about the history of an asteroid and how its evolutionary trajectory is so similar to that of prebiotic Earth.
Results appear in the journal Science.
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QHS Chan et al. 2021. Organic matter and water from the asteroid Itokawa. Sci representative 11, 5125; doi: 10.1038 / s41598-021-84517-x
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