Sylvite and halite on particles recovered from 25143 Itokawa: A preliminary report

We observed cross sectional ultra-thin sections near the surface of 12 particles recovered from the S-type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration-corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer-to-submicrometer-sized sylvite was identified on the surface of Itokawa particle RA-QD02-0034. Separately, micrometer-sized halite was also identified on the surface of Itokawa particle RA-QD02-0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S-type asteroids than previously thought.