Helium from Coronal Mass Ejecta Collected by NASA's Genesis

Abstract

The energy distribution of solar wind (SW) is an indicator of solar activity. The implantation profiles of SW particles in a solid material directly irradiated by the SW echo that energy distribution. Accordingly, the depth distribution of a SW element in a SW collector tells us about the solar activity during the time of collection. Helium is the second most abundant element of SW and almost free from terrestrial contamination, so it is one of the best candidates for measuring a detailed implantation profile. But, analysis of SW He by conventional depth-profiling methods have either extremely low He ionization yields or require extremely large sample volumes. Using the secondary neutral mass spectrometer, LIMAS, at Hokkaido University [1], we previously measured a SW He implantation profile from a bulk solar wind collector from the NASA Genesis SW sample return mission [2]. However, only the shape of the low-speed and high-speed SW He contributions were observed at that time, because the SW He component from coronal mass ejections (CMEs) was below our detection limit. Here we report our new, more sensitive measurements, which show CME flows collected by Genesis in the bulk solar wind collector.

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