Fig. 12

Solar wind ⁴He distribution of asteroid Itokawa sample grain, RA-QD02-0169; olivine. a Backscattered electron image of the Itokawa sample. Red square: ⁴He mapping area. b x–y–z directions of the ⁴He mapping area. x, y: parallel to the surface, z: depth. c Three-dimensional map of ⁴He distribution. Color contours of red color: 10²⁰ He cm⁻³, light gray color: 5 × 10¹⁹ He cm⁻³, and dark gray color: 10¹⁹ He cm⁻³. Cuboid size: (x, y, z) = (8 µm, 13 µm, 525 nm). d ⁴He distribution of x–y plane at z = 50 nm, e He distribution of the x–z cross-section at the line x1 shown in (d). f ⁴He distribution of the y–z cross-section at the line y1 shown in (d). Color contours of (d), (e), and (f) are shown in the figure