| AVS 62nd International Symposium & Exhibition | |
| Helium Ion Microscopy Focus Topic | Thursday Sessions |
| Session HI+AS+NS-ThA |
| Session: | Imaging and Milling with He and Ne Ion Beams |
| Presenter: | Vaithiyalingam Shutthanandan, Pacific Northwest National Laboratory |
| Authors: | V. Shutthanandan, Pacific Northwest National Laboratory R.C. Ogliore, University of Hawai`i at Manoa K. Nagashima, University of Hawai`i at Manoa |
| Correspondent: | Click to Email |
Particles returned from the S-type asteroid Itokawa by JAXA's Hayabusa mission show evidence of space weathering Features. These features can be very small (<1 μm in size) and very shallow (within a 100 nm of the surface). The smallest space-weathering surface features and textures are difficult to resolve by field-emission SEM (FEG-SEM). In order to see these effects, we have used Helium ion microscopy (HIM). Two Hayabusa particles: RB-QD04-0062 (“#62”: 40 μm, olivine and plagioclase) and RB-QD04-0091 (“#91”: 43 μm, olivine and plagioclase) were imaged using HIM. The particles were removed from their glass slides with a Sutter micromanipulator and tungsten needle and then stuck on a SEM stub with a thin layer of Post-It note glue. The stub was coated with ~6 nm of carbon for electrical conductivity. Helium ion microscopy images of the surfaces of two Hayabusa grains revealed diverse space-weathering features on scales from several nm to several μm. Both Hayabusa particles show variable surface textures, a variety of splash melt features, adhering grains, and small holes. Two porous particles, with structures reminiscent of chondritic-porous interplanetary dust particles, were found adhering to the surface of the Hayabusa grains (a 1.2 μm object on #91, a 350 nm object on #62). Much of the surface of #62 was covered with small bumps 25–100 nm in size, whereas other regions were free of small bumps. A large, 6 μm quenched melt splash feature was found on the surface of #62. On the other hand, faces of #91 showed multiple concoidal fractures and splash melt droplets and pancakes, but fewer and smaller surface bumps compared to #62. For comparison purposes a 30 μm grain of lunar soil, which had a much higher density of sub-μm splash melt features than the Hayabusa grains, was also imaged. No obvious impact craters (holes with raised rims) were found on this surface. The variations in surface textures indicate that the grains of Itokawa asteroid experienced a complex history of fracturing and exposure to space-weathering processes on the surface of asteroid Itokawa.