Observing Pluto I

“Experts have long thought that reddish substances are generated as a particular color of ultraviolet light from the sun, called Lyman-alpha, strikes molecules of the gas methane (CH4) in Pluto’s atmosphere, powering chemical reactions that create complex compounds called tholins. The tholins drop to the ground to form a reddish “gunk.” Recent measurements with New Horizons’ Alice instrument reveal that a diffuse Lyman-alpha glow falling on Pluto from all directions in interplanetary space is strong enough to