Pluto haze all in my brain
Lately things don't seem the same
Actin' funny, but I don't know why
'Scuse me while I collapse the sky
— Jimi Hendrix, kinda
A shadow Pluto cast across the Earth reveals that its atmosphere isn't collapsing.
Cool! But yeah, OK, let me explain.
On 29 June 2015, Pluto passed directly in front of a faint star as seen from Earth, creating a kind of mini-eclipse. Pluto has an atmosphere: A very thin one, sure, but it's there. As Pluto moved in front of the star, the atmosphere bent the light passing through it, changing how bright the star appeared. By very carefully measuring that change a lot can be inferred about the atmosphere, including what's in it, how much stuff is in it, and how much it's changing over time.
That's important. Pluto's orbit is highly elliptical, and it's been moving away from the Sun for some time now. Astronomers have thought that it's possible that once Pluto was far enough away from the Sun its temperature would drop so much the atmosphere would collapse: The gas would freeze and fall to the surface as snow until no more atmosphere ...