2020 Volume 49 Issue 1 Pages 1-14
I have been studying mineralogy and petrology of various kinds of extraterrestrial samples: meteorites, Antarctic micrometeorites (AMMs), interplanetary dust particles (IDPs), and fine-grained samples returned from Moon, asteroid (25143) Itokawa, comet 81P/Wild 2, and international space station (ISS). Here I introduce some of my mineralogical studies of extraterrestrial materials by using transmission electron microscope (TEM). I began my meteorite studies during a graduate student, which led me to electron petrography of the extraterrestrial materials by TEM. Next, I describe how I introduced ultramicrotomy to the studies of extraterrestrial materials in Japan. Then, I show some of my studies of AMMs; they are (1) the mineralogy of the vast majority of hydrated AMMs, which is not similar to that of CM chondrites but that of chondritic smooth (CS) IDPs and that of Tagish Lake ungrouped C chondrite, (2) GEMS and enstatite whisker and platelet-bearing highly porous AMMs, which give us another opportunity to investigate samples originated from comets and comet-like icy bodies, and (3) GEMS-bearing AMMs experienced various degrees of aqueous alteration, which shed light on the relationships between CP IDPs and CS IDPs. Then, I introduce micrometeoroids captured at the ISS. A large micrometeoroid revealed similarity to chondrule-like objects recovered from comet 81P/Wild 2 on the standpoint of mineralogy and oxygen isotopic ratios of ferromagnesian silicates. Finally, I show TEM studies of surface modification (space weathering) of Itokawa grains. TEM observation revealed that solar wind is the major cause of the space weathering of the asteorid Itokawa. Some Itokawa grains show blistering on their surfaces, which resulted from the segregation of gaseous species such as H and He near the surface in the space weathering rims.
