Ibitira: A basaltic achondrite from a distinct parent asteroid and implications for the Dawn mission

摘要: I have done a detailed petrologic study of Ibitira, meteorite that has been classified as basaltic eucrite since 1957. The mean Fe/Mn ratio pyroxenes in Ibitira with <10 mole% wollastonite component is 36.4 ±  0.4; this value well resolved from those similar five eucrites studied for comparison, which range 31.2 to 32.2. Data the latter completely overlap. lower Fe/Mg than pyroxenes; thus, higher does not reflect simple difference oxidation state. also an oxygen isotopic composition, alkali element contents, and Ti/Hf distinguish it eucrites. These differences support derivation distinct parent asteroid. Thus, first recognized representative fifth known asteroidal crust, others being HED, mesosiderite, angrite, NWA 011 asteroids. 4 Vesta generally assumed be HED Dawn mission will orbit perform mapping mineralogical, compositional, geophysical studies only subtly different eucritic basalts. A challenge basalt types on surface attempt determine whether indeed