The Heavy Nuclei eXplorer (HNX) Mission

Abstract

The primary scientific objectives of HNX, which was recently selected by NASA for a Small Explorer (SMEX) Mission Concept Study, are to measure the age of the galactic cosmic rays (GCR) since nucleosynthesis, determine the injection mechanism for the GCR accelerator (Volatility or FIP), and study the mix of nucleosynthetic processes that contribute to the source of GCRs. The experimental goal of HNX is to measure the elemental abundances of all individual stable nuclei from neon through the actinides and possibly beyond. HNX is composed of two instruments: ECCO, which measures elemental abundances of nuclei with Z≥72, and ENTICE, which measures elemental abundances of nuclei with 10≤Z≤82. We describe the mission and the science that can be addressed by HNX. 1. Introduction The Heavy Nuclei eXplorer (HNX) mission that is currently being studied as a possible Small Explorer Mission (SMEX) has the primary objective of determining the origin of the galactic cosmic rays. The abundance patterns of the elements and isotopes in the GCRs provide the key because they are the fingerprints of GCR origin. HNX will, for the first time, measure with high precision the abundance of every individual element in the periodic table from neon through the actinides (thorium, uranium, plutonium, curium, and perhaps beyond). The HNX spacecraft will carry two high-precision instruments, the Extremely-heavy Cosmic-ray Composition Observer (ECCO) and the ENergetic Trans-Iron Composition Experiment (ENTICE), which cover overlapping ranges of the periodic table (Figure 1).

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