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2010/11/17

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photoThe Hayabusa capsule after it landed in an Australian desert in June (JAXA)photoJunichiro Kawaguchi, JAXA's project manager for the Hayabusa mission, announces the recovery of asteroid particles on Tuesday. (The Asahi Shimbun)

Scientists have confirmed that the Hayabusa space probe brought back particles from the Itokawa asteroid, the first time materials from an asteroid in the far reaches of space have been recovered.

The Japan Aerospace Exploration Agency (JAXA) said Tuesday that about 1,500 tiny particles taken from the probe's capsule were of extraterrestrial origin.

The particles' compositions matched information about the makeup of Itokawa's surface from infrared photos taken by Hayabusa and from telescope observation.

Junichiro Kawaguchi, the Hayabusa project manager at JAXA, said at the announcement on Tuesday: "Hayabusa's return itself was like a dream, and how could I describe what went beyond a dream?"

The discovery means that Hayabusa's epic 6-billion-kilometer mission was the first to bring back particles from an extraterrestrial object other than the moon or a comet.

Hayabusa, which means falcon, was launched in 2003 and returned to the Earth in June. The probe itself burned up on re-entry, but a capsule containing the particles landed in a desert in Australia on June 13 and was retrieved.

According to JAXA, the particles in the capsule were each less than 0.01 millimeter in size. An electron microscope analysis found that most of the 1,500 particles were made of a hard, greenish mineral called olivine, with some pyroxene and plagioclase dust also present.

Researchers looked at their iron-magnesium ratios and determined that they were different from olivine and other materials on Earth.

The ratio of iron in the Hayabusa particles was about five times higher than in minerals found on Earth.

On the other hand, no igneous material was found among the grains in the capsule even though igneous rocks are common on the Earth's surface, JAXA officials said.

The particles also matched those from meteorites that were once asteroids like Itokawa, according to the officials.

Especially noteworthy was the finding of a type of ion sulfide among the particles. It commonly exists in meteorites but is seldom found on Earth.

"When I saw this crystal (ion sulfide), I pumped my fist in my mind in triumph," said Tomoki Nakamura, an associate professor of planetary science at Tohoku University who analyzed the grains.

The particles will be sent to the SPring-8 synchrotron radiation facility in Hyogo Prefecture, to NASA in the United States, and to other institutions for further analysis.

The particles will be dissected for scrutiny of crystal structures under the microscope. Their three-dimensional structures will be examined in the SPring-8.

Changes in crystals due to exposure to cosmic rays may provide valuable insights into how asteroids are formed. These analyses would also help determine when Itokawa was formed, as well as shed light on its history, including small celestial bodies colliding into it.

Isotope analysis and other examinations could show how much heat Itokawa has been exposed to.

Since Itokawa could be compared to a "fossil of the solar system," having retained its form since around the time the solar system came into being, it could shed more light on the origin of the solar system, the officials said.

The Hayabusa mission was plagued with mishaps and took three years longer than planned.

It touched down on Itokawa twice in November and December 2005, but failed to shoot pellets intended to dislodge rock and sand samples. The particles that were recovered are believed to have been blown into the probe when it was landing.

Communications were cut off after a fuel leak and some of Hayabusa's engines broke down on its return voyage. Only the ingenuity of JAXA scientists managed to get it back to Earth, making it the first probe to return to Earth after landing on a celestial body other than the moon.

The success of the Hayabusa mission demonstrated the durability of th surviving ion engines, which will enable future missions into the far reaches of space, such as to Jupiter.

Its heat-resistance materials could also be applied to other space missions.

JAXA is now planning a second mission, Hayabusa-2, to search for the building blocks of life, such as amino acids, on an asteroid that existed when the solar system was formed, but they face severe problems securing funding and ironing out major technical obstacles.

Researchers hope to launch Hayabusa-2 in 2014. Its development will cost 14.7 billion yen ($177 million).

(This article was written by Masanobu Higashiyama and Shingo Fukushima.)

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