Water found in samples brought from asteroid Ryugu

The Yomiuri Shimbun

TOKYO (Jiji Press) — Water has been found in samples from the asteroid Ryugu brought to Earth by Japan’s Hayabusa2 explorer, according to a study published in the U.S. journal Science.

It is the first-ever discovery of water that takes a liquid form at room temperature from any sample collected outside Earth, according to the study by a team of researchers mainly from Tohoku University and the Japan Aerospace Exploration Agency.

The outcome is expected to lead to better understanding of the origin of the ocean on Earth.

Tohoku University professor Tomoki Nakamura and his teammates analyzed 17 grains of Ryugu sand using systems including the SPring-8 large synchrotron radiation facility in Sayo, Hyogo Prefecture, western Japan.

The team examined the sand grains, 1 to 8 millimeters in size, in detail, looking into their internal structures, mineral composition, hardness and other properties.

As a result, water was found trapped inside tiny holes on iron sulfide crystals inside the sand grains.

It was carbonated water containing carbon dioxide as well as salts and organic matters. The water is believed to have been trapped inside when the crystals formed inside Ryugu’s parent body.

Simulations based on the analysis result has found that the parent body formed on the outer rim of the solar system about 2 million years after the birth of the solar system 4.6 billion years ago.

The parent body was about 100 kilometers in diameter, and the volume of water on it was equal to that of rock. It moved into an orbit closer to Earth and collided with another astronomical body, creating pieces that later gathered to form Ryugu, whose diameter is about 900 meters.

In this process, water mostly evaporated into space, so there is very little left in the present-day Ryugu.

“What we found is the same water that existed abundantly on the parent body. Such astronomical bodies supply water to Earth if they collide with it,” Nakamura said.

“The water contains organic matters and salt, so we found evidence directly linked to the origins of the ocean and organic matters on Earth,” Nakamura said.