It was one of the most energetic particles ever known to strike the Earth -- but where did it come from? Dubbed Amaterasu after the Shinto sun goddess , this particle, as do all cosmic rays that strike the Earth's atmosphere , caused an air shower of electrons, protons, and other elementary particles to spray down onto the Earth below. In the featured illustration , a cosmic ray air shower is pictured striking the Telescope Array in Utah , USA , which recorded the Amaterasu event in 2021 May. Cosmic ray air showers are common enough that you likely have been in a particle spray yourself, although you likely wouldn't have noticed. The origin of this energetic particle, likely the nucleus of an atom , remains a mystery in two ways. First, it is not known how any single particle or atomic nucleus can practically acquire so much energy , and second, attempts to trace the particle back to where it originated did not indicate any likely potential source.
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