2023-07-28 11:50:06
JAXA’s (Japan Aerospace Exploration Agency) asteroid explorer “Hayabusa 2” successfully returned to Earth in December 2020 samples taken from the asteroid “Ryugu” to be explored. Several international research teams are currently analyzing Ryugu samples. Ryugu’s samples, which are said to contain information from the time when the solar system was born, have so far yielded a wide variety of substances, including water, amino acids, noble gases, and carbonated water, as well as information indicating their origins. is found. Also, it is known that Ryugu did not form from the beginning in its present form, but was formed by gathering pieces that were shattered by collisions between celestial bodies. So, even in samples that are only a few millimeters in size, minerals produced in the cold environment of the outer solar system coexist side by side with minerals produced in the very hot environment of the inner solar system. Sometimes I do. What other substances are there?[▲ Figure 1: A0040, one of the samples analyzed this time (Credit: JAXA/ISAS)]An international research team led by Ann. Using a microscope and energy dispersive X-ray spectroscopy, we analyzed Ryugu samples C0002 and A0040. As a result, a total of 58 particles with properties clearly different from those in the surrounding area were found in the sample.[▲ Figure 2: A backscattered electron (BSE) image of the cross section of C0002, and an image that has been colored so that the richer the element, the brighter the color. The delineated region appears dark because it is poor in oxygen (O), magnesium (Mg), and silicon (Si), while it appears bright because it is rich in iron (Fe) and sulfur (S). there is The points indicated by arrows are believed to be olivine, a silicate mineral that does not contain water (Credit: Ann. N. Nguyen, et.al.)】Discovered particles was characterized by a high content of iron and sulfur and a low content of magnesium, silicon and oxygen compared to the surrounding area. As a result of further analysis, it was found that most of these were ‘silicon carbide’ and some were ‘graphite (simple carbon)’. Furthermore, when examining the isotope composition (*1), it was found that the isotopes of carbon, hydrogen, and nitrogen have different ratios from the various substances in the solar system. *1…Even within the same element, those with different atomic weights are called isotopes. Because isotopes behave slightly differently physically and chemically, even the same substance (such as a mineral) with different isotopic composition of the elements contained in it has experienced different environments. It’s one piece of evidence. Since silicon carbide and graphite tend to be altered in the presence of water, it is clear that the regions containing these materials were formed in a water-poor environment. Oxygen-poor and sulphur-rich are other evidences of water and oxygen depletion. On the other hand, evidence has been found that the minerals that make up Ryugu have been altered by liquid water in the past, and the surrounding areas of the particles found this time have also been found to be altered by water. From this, it can be seen that silicon carbide and graphite were mixed following being generated in a different environment than the surrounding minerals. Combined with the fact that the isotope composition is not similar to that of the materials in the solar system, it is possible that these particles existed before the birth of the solar system and are “pre-solar particles” that are remnants of the materials that became the materials of the solar system. is extremely high. The solar system is rich in heavy elements, including carbon. These elements are thought to be produced by stellar activity, supernova explosions, neutron star collisions, etc., but it is not well understood how much each factor contributed to the formation of the elements. However, it was found that the Ryugu pre-solar particles discovered this time were likely produced by a giant star that had entered a stage called the “asymptotic giant branch” (*2). In addition, traces of experiencing a supernova explosion have also been found in some areas. *2…One of the stages of stellar evolution that is thought to occur in the latter half of life for a star that weighs as much as the Sun. Nuclear fusion will occur not only in the center of the star but also in the periphery. In particular, it is noted that there are layers in which carbon is produced. This is not the first time material from before the birth of the solar system has been discovered in samples from Ryugu, and candidates have been found during the initial analysis stage in 2022. However, the difference this time is that more information has been revealed by analyzing a large number of pre-solar particles in detail. This information will be a great clue to clarifying the mysteries of how the materials that make up the solar system were produced, and where carbon, the basis of life, including humans, came from. The Ryugu sample is truly a “Treasure Box” that allows us to know not only the situation immediately following the birth of the solar system, but also the situation before the solar system (pre-solar). The Ryugu samples will continue to reveal many mysteries regarding the solar system.Related ・Origin, history, and cleanliness of asteroid Ryugu revealed Analysis of samples collected from Hayabusa2 (September 30, 2022) ・History of “orbital change of Ryugu” revealed from the isotope ratio of noble gases and nitrogen (November 14, 2022) SourceAnn. N. Nguyen, et.al. “Abundant presolar grains and primordial organics preserved in carbon-rich exogenous clasts in asteroid Ryugu”.
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