Interior textures, chemical compositions, and noble gas signatures of Antarctic cosmic spherules; Possible sources of spherules with long exposure ages

Osawa, Takahito  ; Yamamoto, Yukio*; Noguchi, Takaaki*; Iose, Akari*; Nagao, Keisuke*

The interior texture and chemical and noble gas composition of 99 cosmic spherules collected from the meteorite ice field around the Yamato Mountains in Antarctica were investigated. Their textures were used to classify the spherules into six different types reflecting the degree of heating. An enigmatic spherule, labeled M240410, had an extremely high concentration of cosmogenic nuclides. Assuming 4 exposure to galactic and solar cosmic rays as a micrometeoroid and no exposure on the parent body, the cosmic-ray exposure (CRE) age of 393 Myr could be computed using cosmogenic Ne. Under these model assumptions, the inferred age suggests that the particle might have been an Edgeworth-Kuiper Belt object. Alternatively, if exposure near the surface of its parent body was dominant, the CRE age of 382 Myr can be estimated from the cosmogenic Ar using the production rate of the 2 exposure geometry, and implies that the particle may have originated in the mature regolith of an asteroid.