TOKYO—The Japan Aerospace Exploration Agency (JAXA) announced on Friday that it is asking Science to withdraw one of the 2006 papers that resulted from the Hayabusa asteroid sample return mission because of an error in the data analysis. The retraction won't affect scientists' understanding of the asteroid, however, because other papers have confirmed the study's key conclusions.
The Japanese-led team published a collection of seven papers in a special issue of Science on 2 June 2006 based on observations by four instruments as the Hayabusa spacecraft circled asteroid Itokawa in the fall of 2005. The craft later touched down to grab samples. The paper being retracted, by Tatsuaki Okada and colleagues, presents an analysis of x-ray spectra to determine the elements on the asteroid's surface. The authors concluded "that Itokawa has a composition consistent with that of ordinary chondrites." Chondrites are a type of stony asteroid.
For various reasons, the authors felt they could not rely on the calibration of the instrument done on Earth before the spacecraft was launched. To compensate, they started by assuming they would see the characteristic x-ray spectra of magnesium and silicon, elements known to be present on ordinary chondrites. They then used what they took to be the spectra of those elements to interpret the instrument's raw data. In effect, the authors jumped to a conclusion and then based their analysis on what they expected to observe. (Explanatory materials, in Japanese, are here.)