Hayabusa2 Detects Water-Containing Minerals on Asteroid Ryugu

March 20, 2019

Tokyo- Japan's 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.

Papers on observations results from the Hayabusa2 mission, including the findings, were published on 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 pct of its surface, by using 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 generally uniform in composition exist on the surface at a rate of one pct or less, the team now said.

In addition, comparison with meteorites indicates that rocks that make up Ryugu 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 seem to have broken into smaller pieces and gathered again through collisions with other celestial bodies, the team said.

Considering its volume and mass, Ryugu is rocks and stones aggregated together, like the asteroid Itokawa, which the first Hayabusa probe explored in a mission ended in 2010, according to the team.

At present, Ryugu rotates with 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, making the asteroid look like a spinning top.

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

"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 another key member Seiichiro Watanabe, professor at Nagoya University. Jiji Press