The Hayabusa sample catcher, taken out from the capsule, is opened.
Credit: JAXA/ISIS
An Itokawa dust particle is viewed under optical microscope. The particle is transparent, but contains small black inclusions. The surface of this particle is altered by space weathering.
Credit: JAXA/ISIS
SYDNEY: Dust samples direct from an asteroid have been analysed for the first time, revealing the origin of the most common type of Earth-bound meteorite.
The unmanned Hayabusa spacecraft was launched by the Japan Aerospace Exploration Agency (JAXA) in 2003 to gather a sample from the surface of 25143 Itokawa - a stony, or 'S-type', asteroid. Hayabusa has been riddled with problems, including loss of gyroscopic stabilizers, multiple engine misfires and failures, and a loss of contact with its MINERVA mini-lander, which was designed to land on the asteroid's surface and take images and temperature readings.
Hayabusa was also fitted with a pellet gun that was supposed to dislodge pieces from the surface of the asteroid for analysis. The gun failed to fire, but Hayabusa's dust capture system managed to accidentally collect some of the delicate dust that was kicked up as the craft bounced on the asteroid's surface. Hayabusa returned to Earth in June 2010, landing in the South Australian outback.
"That the gun didn't go off could be regarded as really fortunate, because now we have an unbiased sample of the skin of the asteroid," said co-author Trevor Ireland from the Australian National University in Canberra, of one of the papers published in Science today. "These little dust fragments were sitting on the asteroid's surface and were accidentally carried into the sample return capsule. Getting a sample of the outside skin of an asteroid was one of the goals, so we ended up with a great sample."
Matching chondrites to asteroids
Based on observations from the ground, it was believed that S-type asteroids, typically located in our Solar System's inner and middle asteroid belt, are the material from which most Earth-bound meteorites, known as chondrites, originated.
But without any physical samples from the asteroids, this could never actually be proven, and as the visible spectra of the asteroids never precisely matched those of the chondrites on Earth, many researchers were left doubting what the actual affiliation was between the two.
Only a physical sample from an S-type asteroid could confirm a direct relationship with the most common meteorites on Earth.
Most primitive materials
The first analysis of some of the 1,500 dust grains collected by Hayabusa, led by Tomoki Nakamura from Tohoku University in Sendai, Japan, is one of a number of preliminary studies that have been simultaneously published today.
Nakamura's team used a combination of high-resolution electron microscopes and synchrotron X-ray radiation diffraction methods to characterise the mineralogy of a dust particle. This combination provided information about the sample's chemistry, crystal structure and physical properties.
"The most important goal of the Hayabusa mission is to demonstrate that asteroids are primitive Solar System bodies that record the early Solar System history," said Nakamura. "For this, we need to show asteroidal material is identical to chondrite meteorites, because we already knew that the chondrites are most primitive materials in the Solar System."
