Hayabusa2が持ち帰ったサンプルが示唆すること
小惑星「リュウグウ」の元となった天体には大量の水があったと考えられるそうです。
小さなサンプルから見出される内容が壮大すぎる。。。
先生方はロマンを感じながら研究されたことでしょうと拝察します。
下記はScienceに発表のあった論文からの引用です。
On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective
Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids.
Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft.
We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples.
They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group.
The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal.
The primary minerals were altered by fluids at a temperature of 37 ± 10°C, (ここに入る数値は上の画像参照) million years after formation of the first solids in the Solar System.
After aqueous alteration, the Ryugu samples were likely never heated above ~100°C.
The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.
このアブストラクトには"water"はありませんが、本文を読むとあります。
挑戦してください。
"Formation histroy of Ryugu"のパートとかお勧めです。下記はその一部！
Approximately one to two million years later, roughly 5 million years after Solar System formation (Fig. 5), the material that would later be incorporated into Ryugu experienced aqueous alteration. This caused precipitation of dolomite and magnetite from an aqueous solution at about 37°C. The aqueous alteration of the primary minerals was very extensive. The saponite produced by this fluid-assisted alteration in the parent body must have contained large amounts of interlayer water (~7 wt.%) in its crystal structure, when it formed under saturated water activity, as observed in Ivuna (data S6). The low abundance of interlayer water in the Ryugu samples (0.3 wt.%) indicates that much of this water later escaped to space, most likely after disruption of the parent body and formation of the rubble pile asteroid Ryugu. We cannot definitively identify the dehydration mechanism, but suggest it may have included some combination of impact heating, solar heating, space weathering, and long-term exposure of the asteroid surface to the ultra-high vacuum of space.
