Measuring Pluto's Atmosphere

Astronomers aren't sure exactly how big Pluto is because it's so small and so far away, so trying to measure its wispy atmosphere is clearly a challenge.  Combining two models of that atmosphere, however, has produced an interesting result.

Though tenuous, the atmosphere is still structured, with the upper and lower parts behaving differently.  The atmosphere also expands and contracts depending on Pluto's distance from the Sun.  A new study that combined models of the upper and lower atmosphere suggests that the very top of Pluto's atmosphere may extend almost halfway to the orbit of Pluto's largest moon, Charon-- or roughly 4.5 times the diameter of Pluto itself.