Falling Skies

Pluto's atmosphere is freezing and collaping onto the little world's surface, according to recent reports. Astronomers keep tabs on the atmosphere by watching as stars pass behind Pluto. As a star's light passes through the atmosphere (diagram, top), it reveals the atmosphere's height, density, and other details. New Horizons captured a backlit view of the atmosphere as it sailed beyond Pluto in 2015 (bottom). The atmosphere could completely collapse by 2030 as Pluto continues to move farther from the Sun's warmth. [NASA/JHUAPL/SWRI (2)]