Seven years in deep space

The falcon (Hayabusa) has landed. A few days ago the Japanese space agency's extraordinary craft re-entered the Earth's atmosphere and successfully deposited its sample return capsule in the Australian outback. This was an incredible technological feat, and apart from Apollo and Luna samples from the Moon and the solar particle and cometary dust return missions of Genesis and Stardust, the only other time a spacecraft has made it back to the homeworld possibly carrying scraps of pristine extraterrestrial material. Pristine is the key here. Hayabusa gently bounced off the asteroid Itokawa back in 2005, and may have captured grains of this ancient body that traces an elliptical orbit looping inside that of the Earth before reaching some 70% further out.

Thanks to Hayabusa we know that Itokawa is an extraordinary 'rubble pile' half a kilometer long - not a solid body but rather a loose collection of rocks from tiny pebbles to much larger. Weakly held together by its own gravity this is an amazing snapshot of one episode of planet formation; the agglomeration of solids. Figuring out the precise chemical constituents of a body like this could yield clues to the pathways by which material coalesces in the early stages of a baby star system. It could also add a big piece to the jigsaw puzzle of carbon chemistry in our solar system, and ultimately the origins of terrestrial chemistry.

There's another aspect to Hayabusa that is perhaps even grander. The image of this cleverly fabricated robot burning up across the night sky evokes some powerful emotions. Here is one of our pioneer voyagers of the deeper universe that lies all about us. A persistent machine, nurtured and nursed through a variety of problems by its smart operators. Seven years on it returns, carrying - we hope - a precious sample that will expand our view of nature. Seven years is a long time these days, Hayabusa has come back to a different world. This is a glimpse of our future in the solar system. The meteor-like streaks of returning probes, and eventually astronauts, lighting our skies. New mariners, returning to harbor, bringing exotica that change everything, just as they find a world changed by time.