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Revealing the true nature of asteroids:
HAYABUSA’s historic mission to Itokawa, enabled with NEC technology

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Cover of Science magazine, June 2006 issue

In June 2006, an image of the asteroid Itokawa taken by HAYABUSA graced the cover of the American academic journal Science, which is rivaled in prestige only by its British counterpart Nature. That image heralded a special issue featuring six theses on what HAYABUSA found.
Asteroids are generally imagined to be solid chunks of rock. Around 1990, however, a new hypothesis emerged: they might instead be rubble piles consisting of a loosely bound, highly porous agglomeration of rocks of different sizes.
That hypothesis was first corroborated by HAYABUSA. And a panoply of NEC technology played a key role in bearing it out.
Images taken by the cameras aboard HAYABUSA, and readings taken with its LIDAR laser rangefinder, revealed Itokawa’s shape in three dimensions, enabling its volume to be calculated. Further, its gravity was measured during the spacecraft’s descent and orbit and its density was calculated, making it possible to work out its mass (weight) as well. This analysis of the observed data showed that Itokawa was a low-density object, with an average density of 1.9g per cubic centimeter, confirming that Itokawa was indeed a rubble-pile asteroid — the first to be observed by human eyes.

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Cover of August 2011 issue showing Itokawa's particle image

NEC engineers who had contributed to the success of HAYABUSA’s historic mission were named on the pages of Science as coauthors.
A second special feature, describing the results of analysis of dust particles from the asteroid Itokawa brought back by HAYABUSA, appeared in Science in 2011. That analysis showed that there was a connection between asteroids and meteorites that strike the earth. It also bore out the conclusion that Itokawa was a rubble-pile object reassembled from the fragments of a once-larger asteroid that had disintegrated.
HAYABUSA2’s latest discoveries have likewise been reported in successive issues of Science, and NEC engineers were named in a paper on HAYABUSA2’s findings in the 8 May 2020 issue.

Article by Ayano Akiyama
Published June 11, 2020

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