It’s long been suspected that the meteorites striking Earth come from S-class, or stony, asteroids. The main evidence for that link is the spectra of stony asteroids, which can be measured by telescope. The spectra are almost—but not quite—the same as those of so-called chondritic meteorites, which have chemical abundances that reflect those of the early solar system. Perhaps, some researchers have asserted, the asteroids’ surfaces have been altered by a process known as “space weathering,” but unambiguous proof was missing. Definitive evidence—a sample of dust particles from the surface of a stony asteroid named Itokawa—was supplied by the Hayabusa spacecraft, which was launched in 2003 by the Japan Aerospace Exploration Agency. (The photo—courtesy of JAXA—reveals a kidney-shaped Itokawa, just 535 m long.) A capsule containing Hayabusa’s precious cargo landed in Australia in June 2010. After a year of painstakingly analyzing the sample with cutting-edge tools, researchers recently reported their results. The finding that the grains from Itokawa’s surface have the same composition as chondritic meteorites proves that the meteorites do indeed come from S-class asteroids. (T. Nakamura et al., Science 333, 1113, 2011; H. Yurimoto et al., Science 333, 1116, 2011; M. Ebihara et al., Science 333, 1119, 2011; T. Noguchi et al., Science 333, 1121, 2011; A. Tsuchiyama et al., Science 333, 1125, 2011; K. Nagao et al., Science 333, 1128, 2011.)—Barbara Goss Levi
