The Advanced Composition Explorer measures the chemical composition of the solar wind—high-energy particles from the sun. By comparing it with the compositions of other particles—from meteorites, comets, the moon, the atmospheres of other planets, and the diffuse material that fills the voids between the stars in the galaxy—scientists can better understand the history of our solar system.  

Juno will study the solar wind as it collides into Jupiter's poles and generates dazzling auroras. The spacecraft will also analyze how the solar wind influences Jupiter's magnetosphere—the magnetic bubble that encloses the planet.