SpaceFlight Insider: Charon, a moon of Pluto. When Charon is positioned between the Sun and Pluto, Georgia Tech research indicates that the moon can significantly reduce atmospheric loss. Image Credit: NASA/JHUAPL/SwRI Pluto’s largest moon, Charon, acts as a barrier between the solar wind and Pluto’s atmosphere, preventing that atmosphere from being stripped away when the large moon is positioned between the Sun and Pluto, according to a new study published in the journal Icarus. John Hale and Carol Paty of the Georgia Institute of Technology predicted Charon’s effect on Pluto’s atmosphere before New Horizons returned data from its flyby of the Pluto system. Their findings were confirmed by the spacecraft’s data. Prior to the flyby, Pluto’s atmospheric escape rate was thought to be at least 100 times greater than it actually is. Their study also confirmed another New Horizons finding, specifically that the dark red areas on Charon’s poles are composed of magnetized particles that originated in Pluto’s atmosphere. The large moon is about half Pluto’s diameter, and the two objects are separated by just 12,000 miles (∼19,310 kilometers). This makes them a binary system because their center of gravity is located between the two objects rather than inside the larger one. ...