(JAXA https://bit.ly/3VuCwCL)
Planetary scientists from the University of Hokkaido have determined that the asteroid Ryugu may be related to the comet Wild 2 in the outer solar system.
The team led by Noriyuki Kawasaki came to this conclusion during the analysis of the isotopic composition of oxygen in the primary minerals of the Ryugu samples.
The near-Earth 900-meter asteroid (162173) Ryugu was studied in detail by the Japanese Hayabusa-2 mission.
The spacecraft studied the asteroid from orbit for several years, landed three modules on it and received and delivered to Earth two soil samples, which are now being studied.
This will help to understand a number of interesting questions, like the origin and evolution of Ryugu, and the role of asteroids in delivering water and organic matter to Earth.
The properties of soil samples delivered from Ryugu are similar to those of CI-type carbonaceous chondrite meteorites (the Ivuna type).
They consist mainly of
- phyllosilicates
- carbonates
- magnetite
- pyrrhotite
- anhydrous primary minerals that have undergone changes in a low-temperature medium containing liquid water.
Anhydrous primary minerals formed at high temperatures, such as olivine, low-calcium pyroxene, spinel, hibonite, and perovskite, are rare.
(Kawasaki et al., Science Advances, 2022 https://bit.ly/3jKKMS3)
THE STUDY
Now, Kawasaki's team published the results of a study of the isotopic composition of oxygen (17O and 16O) in primary minerals (olivine, low-calcium pyroxene and spinel).
The group studied the polished sections of particle samples from Ryugu and the Ivuna meteorite using secondary ion mass spectrometry.
This is necessary to impose restrictions on their possible origin.
They found that the distribution of the oxygen isotopic composition in the studied minerals is bimodal.
That means that a substance rich in the 16O isotope is associated with refractory inclusions, and a substance poor in 16O is associated with chondrules.
The ratio of olivine grains rich in 16O to grains poor in this isotope is 3:3 for Ryugu and 7:21 for Ivuna, respectively.
It is hypothesized that the formation of chondrules was a rare event during the formation by accretion of Ryugu parent bodies and CI chondrites compared to other groups of carbonaceous chondrites.
Curiously, the data on the oxygen isotopic composition of Ryugu and Ivuna olivine are similar to those obtained for comet 81P/Wild2.
Both 16O-rich and 16O-poor minerals probably formed in the inner part of the protosolar disk and then could have migrated to the outer part.
It is assumed that the region of formation of Ryugu parent bodies and CI chondrites differs from the regions of formation of other groups of carbonaceous chondrites
That region may also be closer to the region of formation of Comet 81P/Wild2 in the outer Solar System.
This is not the first time attempts have been made to establish a connection between the asteroid Ryugu and comets.
Sources:
- Science Advances: https://www.science.org/doi/10.1126/sciadv.ade2067
- Science Alert: https://www.sciencealert.com/mineral-samples-may-have-just-revealed-the-mysterious-birthplace-of-asteroid-ryugu
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