Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI)

Explanation: PEPSSI will search for neutral atoms that escape Pluto's atmosphere and become charged by their interaction with the solar wind. It will detect the material that escapes from Pluto's atmosphere (such as molecular nitrogen, carbon monoxide and methane), which break up into ions and electrons after absorbing the Sun's ultraviolet light, and stream away from Pluto as 'pickup' ions carried by the solar wind.

Pluto

Image credit: NASA.