National / Science & Health

Hayabusa2 detects minerals containing water on Ryugu asteroid

JIJI, Kyodo

The unmanned space probe Hayabusa2 has detected small amounts of minerals containing water on the surface of the asteroid Ryugu, a Japanese research team has said.

The findings may provide a clue to solving the mystery of the origin of Earth’s water. Scientists say that at least part of the water came from asteroids and comets.

Research from the Hayabusa2 mission was published through the online version of the U.S. journal Science on Tuesday.

Ryugu is classified as a C-type asteroid containing water and organic compounds.

After its arrival at Ryugu in June last year, Hayabusa2 surveyed 69,000 locations on the asteroid, covering 90 percent of its surface, by using a near-infrared spectrometer capable of detecting hydrated minerals.

But the team said in August that year that its analysis of the observation data did not find anything indicating the presence of water.

Later, the team redid its analysis after adjusting for measuring errors.

The fresh analysis has found that hydrated minerals that are mostly uniform in composition exist on the surface at a rate of 1 percent or less, the team said.

“The decision to choose Ryugu as the destination, based on the prediction that there is some water, was not wrong,” said Kohei Kitazato, an associate professor at the University of Aizu in Fukushima Prefecture.

In addition, comparing the rocks that make up Ryugu with meteorites indicates that they are likely to have been heated in the past, according to the team.

Observation results obtained so far suggest the possibility that Ryugu originated from the parent body of the Polana or Eulalia asteroid family. Both families are in the asteroid belt between the orbits of Mars and Jupiter.

Rocks that make up Ryugu are believed to have been heated inside its parent body, which was created 4.56 billion years ago, just after the solar system was formed.

After losing water due to the heating, the rocks appear to have broken into smaller pieces and gathered again through collisions with other celestial bodies, the team said.

Considering its volume and mass, the team believes Ryugu is made of rocks and stones aggregated together — in similar fashion to the asteroid Itokawa, which the first Hayabusa probe explored in a mission that ended in 2010.

At present, Ryugu rotates over a period of 7.6 hours. But it used to spin much faster, with a rotation period of 3.5 hours. This caused its shape to bulge at an equatorial area due to centrifugal force, giving the asteroid the appearance of a spinning top.

“Detailed observations of Ryugu are beginning to shed light on its history,” said University of Tokyo professor Seiji Sugita, a key member of the team.

“We’d be able to collect precious samples that will help unravel what happened 4.5 billion years ago” if the Hayabusa2 mission succeeds in bringing the samples to Earth, said Nagoya University’s Professor Seiichiro Watanabe, another key member of the team.