A Japanese spacecraft that landed on an asteroid found a ball of rubble held loosely together by its own gravity, unlike other asteroids that have been visited, according to reports from the mission published this week.
The spacecraft Hayabusa, whose name means “falcon” in Japanese, hovered over the near-Earth asteroid Itokawa last autumn, taking several measurements before landing briefly on the orbiting gravel pile.
Itokawa has two parts resembling the head and body of a sea otter, Akira Fujiwara and his colleagues report in Friday’s issue of the journal Science. Previously studied asteroids appeared to be lumps of solid rock, but Itokawa is made up of loosely packed bits of sand and boulders, they said. Their findings could have implications for deflecting asteroids that might pass too close to Earth in the future.
“We’ve never had a close-up look at such a small asteroid until now,” said Brown University's Takahiro Hiroi, who worked on the study, a joint U.S.-Japanese effort. “Large asteroids such as Eros are completely covered with a thick regolith — a blanket of looser material created by space weathering. With Itokawa, we believe we have witnessed a developing stage of the formation of this regolith.”
Itokawa is very small, just 500 yards (meters) long. But it is close in astronomical terms, orbiting 321 million miles (513 million kilometers) from Earth. Although it does not threaten to collide with Earth, it makes a tempting scientific target.
Nearly a miss
Hayabusa very nearly did not make it.
The little spacecraft, now bringing a sample capsule back to Earth, uses an ion propulsion system, whose efficiency should be critical to future missions in deep space.
At one point, Hayabusa lost communication with its controllers, Erik Asphaug of the University of California at Santa Cruz wrote in a commentary in Science.
“Its hydrazine (fuel) had leaked away shortly after the second sample collection attempt. Two of the reaction wheels had failed and the battery was dead. Adding insult to injury, Minerva — intended to be the first asteroid surface robot — had been released during an unexpected maneuver and was lost to space,” he added.
“Yet despite these heartbreaking setbacks, Hayabusa has been a stunning success both for asteroid science and for deep-space concept testing.”
Asphaug said information delivered by the spacecraft “enhances our understanding of near-Earth objects.”
“Near-Earth objects are not only important scientifically — our planet formed from them — but have also become political hot potatoes, given the growing pressure to do something to mitigate the risks they may pose to Earth,” he said.
The spacecraft, launched in 2003, is expected to glide back to Earth in 2010 and crash-land in the Australian desert. It is not yet clear whether Hayabusa actually succeeded in collecting any samples.