Organic Matter And Water

An international team of scientists has studied both the water and organic contents from 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 asteroidal materials to Earth.

The S-type asteroid Itokawa. Image credit: JAXA.

The S-type asteroid Itokawa. Image credit: JAXA.

“Understanding the earliest chemical reactions involving liquid water provides crucial insights to how simple building blocks of organic compounds evolved into increasingly complex macromolecules via actions of water,” said lead author Dr. Queenie Chan from the Department of Earth Sciences at Royal Holloway and colleagues.

“Such investigation necessitates the availability of pristine samples of astromaterials — samples that have not been compromised by terrestrial contamination, and thus preserve the intrinsic states of the materials’ physical, chemical, organic and other properties.”

“Studying freshly collected, cleanly curated astromaterials returned by spacecraft reduces the ambiguity of terrestrial exposure that meteorite samples have typically experienced.”

In 2010, the Hayabusa mission successfully recovered over thousands of regolith particles, with sizes ranging 10-200 μm, from the near-Earth asteroid Itokawa.

“Itokawa is considered a rubble-pile asteroid that was re-accreted from materials of a formerly large, thermally metamorphosed, collisional-disrupted 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 — came from.”

“Ordinary chondrites typically have low organic contents. Hence, their organic analyses had been challenging, which is more so in the case of minute-sized returned samples of small total recovered mass.”

The chemical distribution and mineralogy of the Amazon particle from the S-type asteroid Itokawa: (A) image showing Amazon being picked up using a glass needle with platinum wires at JAXA; (B) photomicrograph taken in visible light of Amazon before and after being mounted into indium; (C) EDX combined Mg-Si-Al X-ray maps (Mg is red, Si is blue, Al is green) of Amazon, grids are 10 µm 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), pyroxene (red) and OM (yellow); locations of primitive OM (p-OM) and mature OM (m-OM) are marked by the italicized annotations, NanoSIMS spot analyses of albite (Ab), olivine (Ol) and pyroxene (Py) are marked as open squares, and the area of NanoSIMS imaging analysis is marked as dashed square; (E) EDX spectra of olivine, pyroxene and albite, locations of the points are shown in (C); and (F) selected Raman spectra of the mineral and organic components in Amazon; peak positions of their characteristic Raman modes are shown as the dotted lines in their corresponding colors; (G) selected Raman spectra of Amazon olivine compared to heated chondrite LL5 Alta-ameem; (H) Selected Raman spectra of Amazon organics compared to that of primitive and heated chondrites. Image credit: Chan et al., doi: 10.1038/s41598-021-84517-x.

The chemical distribution and mineralogy of the Amazon particle from the S-type asteroid Itokawa: (A) image showing Amazon being picked up using a glass needle with platinum wires at JAXA; (B) photomicrograph taken in visible light of Amazon before and after being mounted into indium; (C) EDX combined Mg-Si-Al X-ray maps (Mg is red, Si is blue, Al is green) of Amazon, grids are 10 µm 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), pyroxene (red) and OM (yellow); locations of primitive OM (p-OM) and mature OM (m-OM) are marked by the italicized annotations, NanoSIMS spot analyses of albite (Ab), olivine (Ol) and pyroxene (Py) are marked as open squares, and the area of NanoSIMS imaging analysis is marked as dashed square; (E) EDX spectra of olivine, pyroxene and albite, locations of the points are shown in (C); and (F) selected Raman spectra of the mineral and organic components in Amazon; peak positions of their characteristic Raman modes are shown as the dotted lines in their corresponding colors; (G) selected Raman spectra of Amazon olivine compared to heated chondrite LL5 Alta-ameem; (H) Selected Raman spectra of Amazon organics compared to that 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 its unique shape resembling the South America continent preserved after soft pressing into indium — recovered from Itokawa.

Using energy dispersive X-ray (EDX) spectroscopy and Raman analysis, they detected both primitive (unheated) and processed (heated) organic matter — presented as both nanocrystalline graphite and polyaromatic carbon — within ten microns of distance.

Their results suggest that Itokawa has been constantly evolving over billions of years by incorporating extraterrestrial water and organic materials.

In the past, the asteroid will have gone through extreme heating, dehydration and shattering due to catastrophic impact.

However, despite this, Itokawa came back together from the shattered fragments and rehydrated itself with water that was delivered via the in fall of dust or carbon-rich meteorites.

“The organic matter that has been 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 in fall of primitive organics arrived on the surface of Itokawa after the asteroid had cooled down.”

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 traditional views on the origin of life on Earth which have previously heavily focused on C-type carbon-rich asteroids.

“Studying ‘Amazon’ has allowed us to better understand how the asteroid constantly evolved by incorporating newly-arrived exogenous water and organic compounds,” Dr. Chan said.

“These findings are really exciting as they reveal complex details of an asteroid’s history and how its evolution pathway is so similar to that of the prebiotic Earth.”

The results appear in the journal Science.

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Q.H.S. Chan et al. 2021. Organic matter and water from asteroid Itokawa. Sci Rep 11, 5125; doi: 10.1038/s41598-021-84517-x

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