Observations of the asteroid Ryugu help to understand the history of its loss of water into space

(ORDO NEWS) — Last month, Japanese spacecraft Hayabusa 2 delivered rock samples collected from the surface of a near-Earth asteroid called Ryugu to Earth. While these samples are being analyzed in laboratories, scientists are using other data collected using the scientific instruments of the apparatus to obtain new information about the past of the asteroid under study.

In a new scientific paper, the researchers offer an explanation for the fact that the asteroid Ryugu contains fewer hydrated, or water-containing minerals than some other asteroids. According to the study, the ancient parent body that formed the asteroid Ryugu likely lost water as a result of the heating event, even before the asteroid formed.

One of the reasons the asteroid Ryugu was selected as the scientific target of the Hayabusa 2 mission is that the surface of this space rock is relatively dark, which may indicate the presence of hydrated minerals or organic compounds. Asteroids containing water are of interest to scientists, since with such asteroids the water could have been delivered to Earth, thanks to which the emergence of life became possible on it.

However, in the course of observations of the asteroid Ryugu with the help of the Hayabusa-2 apparatus, it turned out that the asteroid contains less water than expected. To explain the loss of water by this asteroid into space, several mutually exclusive versions have been proposed.

Asteroid Ryugu is a conglomerate of small stones, so scientists believe that it was formed as a result of the gradual sticking together of debris formed as a result of collisions between large asteroids. In this case, the water could have been lost by the parent asteroid as a result of warming up during the collision, and the asteroid Ryugu subsequently formed as a result of sticking together of “dry” stones. An alternative version suggests that the asteroid Ryugu, containing at first a normal amount of water on the surface, passed near the Sun several times, after which the water quickly evaporated.

In the new work, scientists led by Kohei Kitazato of Aizu University, Japan, were able to determine in favor of one of these two hypotheses by analyzing the results of observations of the surface of the asteroid Ryugu using the onboard spectrometer of the Hayabusa-2 spacecraft. When Hayabusa 2 fired a projectile into an asteroid in 2019, forming a funnel on it, scientists found that the subsurface material showed the same reflectivity, indicating an extremely low content of hydrated minerals, as the material of the upper soil layer. This made it possible to exclude the hypothesis of water volatilization from the surface of the asteroid Ryugu as a result of heating by the rays of the Sun and left only possible the assumption of the formation of this cosmic “heap of debris” from “dry” stones, the authors explained.


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