2005

Hayabusa at Itokawa

Possible future impacts of Earth by asteroids or comets represent a threat to the entire human species. As such, studying small bodies and learning about their orbits and properties is appropriately an international endeavor. During the late twentieth and early twenty-first centuries, space missions by the US, European, and Russian space agencies to comets Halley, Borrely, Wild-2, and Tempel-1, and the asteroids Gaspra, Ida, Mathilde, Eros, and Lutetia, dramatically increased our understanding of kilometer-size (or tens-of-kilometers-size) bodies. But it wasn’t until the mission of the Japanese Hayabusa spacecraft that a truly tiny asteroid was studied in detail.

Hayabusa, Japanese for “falcon,” was the first asteroid mission by the Japanese Aerospace Exploration Agency (JAXA) and the first attempted robotic sample return from an asteroid. Launched in 2003, Hayabusa used novel ion propulsion engines to slowly and gently match its trajectory to that of a small, recently discovered near-Earth asteroid named 25143 Itokawa.

In September 2005 the spacecraft began its rendezvous alongside Itokawa (the asteroid’s gravity was too low to allow the spacecraft to truly orbit), which turned out to be a gray, elongated, rocky object only about 1,750 feet (535 meters) long. Large boulders and strangely smooth areas were discovered covering the surface of the lumpy little world. Two months later Hayabusa was directed to approach even closer to the asteroid, and to gently touch down, release a small rover, collect some surface soil and rock samples, and then return a sample capsule to Earth. No problem, right?

In reality there were lots of problems. Hayabusa landed on the asteroid, briefly, but the rover deployment failed, and the spacecraft ascended out of control from the surface before it could be confirmed that it had gathered samples. By the time control was regained, it was too late to try again; the sample capsule had to be launched back to Earth without knowing whether or not it was empty.

The sample capsule made a safe parachute landing in Australia in June 2010, and after some tense weeks of careful unpacking and testing, scientists were delighted to find about 1,500 small dusty grains of Itokawa inside, with chemistry matching that of some primitive meteorites. Hayabusa was a success!

Near-Earth asteroid 25143 Itokawa, photographed by the Japanese Aerospace Exploration Agency’s Hayabusa spacecraft in September 2005. Itokawa is a tiny lump of silicate rock, only about 1,750 feet (535 meters) long, or about the length of six New York City blocks.