When NASA's New Horizons spacecraft flew past Pluto in 2015 and then looked back, the photo it took stopped people in their tracks. It showed Pluto from behind, lit from the far side by the distant Sun — and floating around it was a delicate, glowing, blue ring. Pluto's atmosphere. Tiny, fragile, and beautiful. Mission scientist Alan Stern said simply: "Who would have expected a blue sky in the Kuiper Belt? It's glorious."
Yes. Pluto has a very thin atmosphere made mostly of nitrogen, with small amounts of methane and carbon monoxide. It is about 100,000 times thinner than Earth's atmosphere — you couldn't breathe it. The sky is blue. And every 248 years, when Pluto reaches the far end of its orbit, the whole atmosphere freezes and falls to the ground as snow.
What Pluto's Atmosphere Is Made Of
If you could scoop up a small sample of Pluto's air, you would find:
- Nitrogen — the main gas, just like in Earth's atmosphere
- Methane — the same gas burned in kitchen stoves on Earth
- Carbon monoxide — the gas that comes out of car exhaust pipes
There is no oxygen. None at all. You would suffocate in seconds even if the cold didn't get you first. And the whole atmosphere is so thin — about 10 microbars of pressure compared to Earth's 1,000,000 microbars — that even on the ground it's closer to space than to sea level.
Why the Sky Is Blue
Earth's sky is blue because tiny molecules in the air scatter blue light from the Sun in every direction. Blue is the colour with the shortest wavelength of visible light, so it bounces around the most. Pluto's sky is blue for almost the same reason — but with a twist.
Pluto's blue comes from tiny haze particles called tholins, which form high up in the atmosphere when sunlight hits the methane. The tholins are the same chemicals that paint Pluto's surface red. Up high they scatter blue light beautifully. Lower down they drift onto the surface as a fine reddish snow over billions of years. The same chemicals create a blue sky and a red ground. More on Pluto's red surface.
Imagine standing on Pluto. The Sun is a bright star. The sky is a thin, dim blue band on the horizon, fading to black just a short way up. Above your head is space, almost. The atmosphere is so thin you can see the stars even when the Sun is up. And it would still feel like dusk, with no shadows, because the Sun is too small to cast them well.
The 20 Layers of Haze
When New Horizons looked sideways through Pluto's atmosphere, it found something nobody had predicted. The atmosphere isn't a smooth blanket. It is made of about 20 separate layers of haze, stacked one above the other, rising more than 200 km above the surface.
Each haze layer is thin and faint, but they show up clearly when sunlight passes through them sideways. Nobody is completely sure why they form, but scientists think the layers are caused by ripples in Pluto's gravity as it spins, plus the way different chemicals freeze out at different heights.
The Freeze-Thaw Cycle
The most amazing thing about Pluto's atmosphere is that it isn't always there. Every 248 years, when Pluto reaches the farthest point in its long oval orbit, it gets so cold that the atmosphere freezes solid and falls to the ground as snow. Then, when Pluto swings back closer to the Sun, the snow turns back into gas and the atmosphere reforms.
This freeze-thaw cycle is sometimes called "the Breath of Pluto." Pluto is the only world we know that has a complete atmosphere that comes and goes every year.
It thaws.
It breathes.
It freezes.
It falls.
Every 248 Earth years, the whole sky comes back.
Pluto last reached the closest point in its orbit (perihelion) in 1989, when its atmosphere was at its thickest. Since then it has been creeping away from the Sun. Scientists have been watching closely to see when the atmosphere will start to freeze and collapse. Predictions say sometime in the 2030s, although early measurements suggest the freeze may have already started. By the late 2100s, much of Pluto's atmosphere will be locked up on the ground as ice. Then around 2237, perihelion will come back, and the air will rise again. More on Pluto's orbit and timing.
Charon Gets a Free Coat of Methane
Here is a strange side-effect of Pluto's thin atmosphere. The gas keeps slowly leaking out into space. Some of that leaking methane gets pulled across by Charon's gravity, and freezes onto Charon's north pole. The frozen methane reacts with the Sun's UV light and becomes red tholin — the same way it does on Pluto. So Charon's north pole is a huge red patch called Mordor Macula, painted entirely by gas escaping from Pluto. Pluto is literally painting its own moon. More on Charon.
Pluto's atmosphere is so thin that the sky never goes properly bright. Even at high noon, the sky stays dim and you can still see stars overhead. The whole atmosphere only weighs about as much as a small mountain range. That's the entire planet's air, total.
Above the haze, almost nothing.
Pluto stops, and space begins.
Pluto's atmosphere freezes because of its long stretched orbit → More on Pluto's orbit. The tholins make the sky blue and the surface red → Pluto's surface. Or jump back to the main Pluto facts page.
Frequently Asked Questions
Does Pluto have an atmosphere?
Yes. Pluto has a very thin atmosphere made mostly of nitrogen, with small amounts of methane and carbon monoxide. It is about 100,000 times thinner than Earth's atmosphere, but it has clouds, haze layers, and a faint blue sky.
What is Pluto's atmosphere made of?
Pluto's atmosphere is mostly nitrogen, the same main gas as Earth's air. It also contains methane (the gas used in kitchen stoves) and carbon monoxide. There is no oxygen, so it isn't breathable.
Why is Pluto's sky blue?
Pluto's sky is blue because tiny haze particles called tholins scatter blue light from the Sun better than other colours. The tholins form when sunlight breaks apart methane gas high in Pluto's atmosphere. The same tholins drift down to paint Pluto's surface red.
Does Pluto's atmosphere freeze?
Yes. When Pluto moves far away from the Sun on its long oval orbit, it gets so cold that the nitrogen in its atmosphere freezes solid and falls to the ground as snow. Then, when Pluto moves closer to the Sun again, the ice turns back into gas. This cycle takes 248 Earth years.
Can you breathe Pluto's air?
No. Pluto's atmosphere is about 100,000 times thinner than Earth's, and it contains no oxygen at all. Even if you could survive the cold (−229 °C), you would suffocate within seconds.