Hayabusa asteroid probe faces moment of truth

Following a mishap during its rendezvous with an asteroid in 2005, and other technical problems, the Japanese spacecraft Hayabusa was all but given up for dead.

Miraculously it has been nursed back to life, and it is now hurtling towards Earth, on track to hurl a small but potentially momentous capsule into the Australian outback on Sunday, 13 June.

No one knows whether Hayabusa managed to grab a dust sample when it landed on the asteroid Itokawa. If it did, this would be a first. Even more significantly, the dust will give us clues as to how the Earth formed, as well as insights into how to prevent it being destroyed by an asteroid impact. Find out more in this New Scientist briefing.

Where is Hayabusa now?
At 0900 Japan time today (11 June) the Japan Aerospace Exploration Agency (JAXA) announced that Hayabusa was 1,142,550 kilometres from home, following its fourth and final "trajectory correction manoeuvre" on Wednesday. This nudged Hayabusa into the position needed for an 18-kilogram capsule – hopefully containing a sample of asteroid soil – to land at the intended target, the Woomera test tange in South Australia.

How will the Hayabusa land?
Three hours before re-entry, when the spacecraft is 40,000 kilometres from Earth, Hayabusa will release its sample recovery capsule. The capsule will then enter the atmosphere as a fireball, experiencing temperatures of up to 3000 °C, says Hitoshi Kuninaka, a senior member of the Hayabusa project at JAXA.

At an altitude of 10 kilometres, the capsule will deploy a parachute and an antenna that will be used to track it as it lands at Woomera. Once the landing point is confirmed, the capsule will be collected and airfreighted to Japan. Only when it has reached the Sagamihara Curation Center near Tokyo will we know what, if anything, is inside.

What went wrong on Itokawa?
When Hayabusa landed on the asteroid in 2005, it was supposed to fire two metal pellets onto its surface, pushing up material into the cone-shaped sampling capsule for collection. But just after landing, the fuel thruster leaked, causing the spacecraft to enter a "safe" mode, in which all unnecessary systems were shut down.

Given the malfunction, how could the capsule contain any dust?
Because gravity on Itokawa is extremely weak, Hayabusa is likely to have puffed up a plume of dust when it landed. Kuninaka is hopeful that some of this may have entered the capsule, though he admits there is no evidence this has happened.

Michael Zolensky, curator of stratospheric dust at the Astromaterials Research and Exploration Science directorate at NASA Johnson Space Centre in Houston, Texas, also predicts that there is something interesting inside the capsule. Even microscopic samples could be "sliced up" and analysed to give information about the chemical composition of asteroids, he says.