Australasian Science: Australia's authority on science since 1938

What Does the Hyabusa Asteroid Sample Tell Us?

By Trevor Island

Last year the Hayabusa capsule landed in South Australia with a sample of dust collected from the Itokawa asteroid. The dust has now been analysed and the results of the preliminary investigation published in Science. Here the only Australian involved in the research outlines its significance.

“The Hayabusa mission has provided us with samples of a pristine asteroid – and what a message it contains.

“We can now unequivocally link the asteroids we see in space with meteorites that we collect on land. There have been problems relating the nature of asteroids with meteorites because meteorites are ablated as they come in through the atmosphere. The samples from Itokawa are the previously unknown ‘skin’ of an asteroid.

“It should be noted that the original intent was for a gun to fire into the surface of Itokawa when Hayabusa touched down, with the ejected sample collected into the sample chamber. This would have provided us with a bulk sample of the asteroid to analyse. However, a software interlock prevented the gun from firing. This was disappointing in that we did not get as much material returned as was intended.

“In hindsight though, a bulk sample would not necessarily have provided the same information as we have obtained from these small dust grains that sat on the very surface of the asteroid. These were the samples we really wanted and these have been delivered back to us.

“These samples illustrate the dynamic nature of the solar system. The samples from the skin of the asteroid show that they have been exposed to cosmic rays and solar wind for less than 10 million years. This is very young in solar system terms. The ages of the parent bodies are over 4.5 billion years old, and when the parent body of Itokawa had a collision, material was broken off and reassembled into Itokawa and sent on an orbit through the inner solar system.

“This demonstrates how the inner solar system asteroids are only with us for a short time (geologically speaking). They are ejected from the asteroid belt and their orbits will decay until they fall into the Sun, collide with the planets, or otherwise get accelerated away when they come in close proximity to the planets.”

Trevor Ireland, Professor of Earth Chemistry, The Australian National University, is co-author on two of the papers published. Source: AusSMC