Japan, U.S. Fund Study of Asteroid Itokawa Composition

Washington - For the first time, in work funded by NASA and the Japanese Aerospace Exploration Agency (JAXA), a group of scientists have an intimate look at a small asteroid called Itokawa.

Using data from the Japanese space probe Hayabusa, launched by JAXA in 2003, the team has determined the mineral makeup and surface characteristics of the asteroid and published their findings in the journal Science.

Itokawa, a potato-shaped, near-Earth asteroid, consists mainly of the minerals olivine and pyroxene, a composition similar to a that of stony meteorites that have pelted Earth in the past, according to a June 1 press release from Brown University in Rhode Island.

The asteroid ingredient list comes courtesy of Hayabusa, whose mission is to bring back first-ever samples from an asteroid to better understand their role as building blocks of the solar system.

The elongated rocky asteroid is nearly as long as five football fields and circles the sun more than 516 million kilometers away from Earth.

Along with a few hundred known asteroids, Itokawa’s orbit is close to Earth’s orbit and was discovered by the Lincoln Near-Earth Asteroid (LINEAR) program, which detects near-Earth asteroids and provides advance warning if any are bound for Earth.

LINEAR is a Massachusetts Institute of Technology Lincoln Laboratory program funded by NASA and the U.S. Air Force.

Itokawa does not pose a threat to Earth, but its proximity made it a tempting scientific target.  A near-infrared spectrometer aboard Hayabusa helped identify Itokawa’s mineralogy, mostly a mixture of the rock-forming minerals olivine and pryroxene, and possibly some plagioclase and metallic iron.

But to truly understand what they had, the team turned to Takahiro Hiroi, a Brown University researcher who is expert in determining the composition of asteroids and meteorites, bits of asteroids that have fallen to Earth.

Hiroi is operations manager of the university’s NASA-funded Reflectance Experiment Laboratory (RELAB).

For the Hayabusa project, Hiroi obtained samples of meteorites from museums, measured them at RELAB, and compared the results with data from Itokawa.  He determined that the mineral composition of the surface of Itokawa was similar to that of a common class of stony meteorites relatively low in metallic iron.

This link helped the team place a probable source of origin for Itokawa: the inner portion of the main asteroid belt, a ring of tens of thousands of rocks orbiting the sun between Mars and Jupiter.

Using Hayabusa data, the team also was able to better describe the surface of Itokawa, much of which is studded with boulders, although the asteroid contains a smoother area known as Muses Sea.

This diversity of terrain, the team concluded, might be the result of past meteoroid impacts and space weathering, a rock-altering process due to bombardments by dust particles and solar wind.

“We’ve never had a close-up look at such a small asteroid until now,” Hiroi said.

The full text of the press release is available at the Brown University Web site.

For additional information, see Science and Technology.