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Anomalous cosmic rays (ACRs) are cosmic rays with less than the usual energy. They are thought to be formed when neutral atoms hit the edge of the solar system (the heliosheath) and are ionized and accelerated. This is presumed to accelerate the protons to a slower velocity than the "normal" cosmic rays produced by some kind of more-distant mechanism. A more recent theory is that ACRs are caused by magnetic reconnection.