An international team of scientists studied the water and organic content of a dust particle recovered from the surface of near-Earth S asteroid 25143 Itokawa by JAXA’s Hayabusa mission, which was the first mission to trace pristine asteroid materials to brought the earth.
The S-type asteroid Itokawa. Image credit: JAXA.
“Understanding the earliest chemical reactions with liquid water provides crucial insights into how simple building blocks of organic compounds evolved into increasingly complex macromolecules through the action of water,” said lead author Dr. Queenie Chan, of the Department of Earth Sciences at Royal Holloway and colleagues said.
“Such an investigation necessitates the availability of pristine samples of astromaterials – samples that have not been affected by terrestrial pollution, and thus preserves the intrinsic conditions of the material’s physical, chemical, organic and other properties.”
“The study of freshly collected, clean-curated astromaterials returned by spacecraft reduces the ambiguity of exposure to Earth that meteorite samples typically experienced.”
In 2010, the Hayabusa mission successfully recovered over thousands of regolith particles, with sizes ranging from 10-200 μm, from the near-Earth asteroid Itokawa.
“Itokawa is considered a debris asteroid that was re-incorporated from materials of a previously large, thermally metamorphosed, collision-disturbed precursor planetesimal,” the researchers said.
“S-type asteroids are one of the most common objects in the inner asteroid belt, where most of the earth’s meteorites – ordinary chondrites – come from.”
‘Ordinary chondrites usually have a low organic content. Therefore, their organic analyzes were challenging, which is more to do in the case of minute-sized samples with a small total recycled mass. ‘
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 wires at JAXA; (B) micrograph taken in visible light from Amazon before and after it was mounted in indium; (C) EDX combined Mg-Si-Al X-ray charts (Mg is red, Si is blue, Al is green) from Amazon, grids are 10 grootm in size; locations of EDX spectra in (E) are shown as points 1-3, and (D) Raman map of Amazon showing mineralogical distribution of olivine (green), plagioclase (blue), pyroxine (red) and OM (yellow) ; locations of primitive OM (p-OM) and mature OM (m-OM) are characterized by italicized notes, NanoSIMS carbon analyzes of albite (Ab), olivine (Ol) and pyroxene (Py) are marked as open squares, and the area of NanoSIMS image analysis is as an underlined square; (E) EDX spectra of olivine, pyroxene and albite, the location of the points being shown in (C); and (F) Raman spectra of the mineral and organic components selected in Amazon; peak positions of their distinctive Raman modes are shown as the dotted lines in their corresponding colors; (G) selected Raman spectra from Amazon olivine compared to heated chondrite LL5 Altaem; (H) Selected Raman spectra of Amazon organics 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 co-authors analyzed a single grain, nicknamed ‘Amazon’, to recognize the unique shape that resembles the continent in South America preserved after soft impression in Indium. It was recycled from Itokawa.
Using energy-dispersing X-ray (EDX) spectroscopy and Raman analysis, they detected primitive (unheated) and processed (heated) organic matter – presented as both nanocrystalline graphite and polyaromatic carbon – within ten microns.
Their results suggest that Itokawa has continuously evolved over billions of years by incorporating extraterrestrial water and organic materials.
In the past, the asteroid will overheat, dry out and shatter due to a catastrophic impact.
Despite this, however, Itokawa recovered from the broken fragments and re-watered it with water produced by the fall of dust or carbon-rich meteorites.
“The organic material that has been heated indicates that the asteroid has been heated to more than 600 degrees Celsius in the past,” said dr. Chan said.
“The presence of unheated organic matter very close to it means that the autumn of primitive organic matter arrived on the surface of Itokawa after the asteroid cooled.”
The findings also show that S-type asteroids, where most of Earth’s meteorites come from, such as Itokawa, contain the raw ingredients of life.
The analysis of this asteroid changes the traditional views on the origin of life on earth, which previously focused strongly on C-carbon rich asteroids.
“Studying ‘Amazon’ has enabled us to better understand how the asteroid has evolved continuously by ingesting newly arrived exogenous water and organic compounds,” said dr. Chan said.
“These findings are very exciting, as they reveal intricate details of the history of an asteroid and how its evolutionary path is so similar to that of the prebiotic Earth.”
The results appear in the journal Science.
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QHS Chan et al. 2021. Organic matter and water from the asteroid Itokawa. Scientific Rep 11, 5125; doi: 10.1038 / s41598-021-84517-x