Pluto’s Blue Sky: It’s More Than Just a Pretty Picture
Pluto blue sky

I don’t think New Horizons has sent back a bad picture of Pluto yet. And today is no different. The latest picture of Pluto isn’t of its surface. Today, NASA shows us what color Pluto’s haze (and sky) is. It’s blue!

blue sky Pluto

New Horizons Principal Investigator Alan Stern sums it up best, “who would have expected a blue sky in the Kuiper Belt? It’s gorgeous.”

Pluto’s blue sky is incredible, but there’s science here too

“That striking blue tint tells us about the size and composition of the haze particles,” said science team researcher Carly Howett, also of SwRI. “A blue sky often results from scattering of sunlight by very small particles. On Earth, those particles are very tiny nitrogen molecules. On Pluto they appear to be larger — but still relatively small — soot-like particles we call tholins.”

So, what are tholins? They form after ultraviolet sunlight breaks apart and ionizes nitrogen and methane molecules. This process allows them to form more complex negatively and positively charged ions. Once they recombine, they form intricate macromolecules. And finally, volatile gases condense and coat the surfaces of these macromolecules as they fall back to Pluto’s surface.

A similar process was first observed in the upper atmosphere of Saturn’s moon Titan.

New Horizons spots small pockets of water ice

Just when you thought today’s news could get any cooler, New Horizons also revealed several regions of exposed water ice. See the blue highlighted areas in the image below? That’s where water ice was detected.

water-ice pluto

But, what about the rest of Pluto’s surface? Why water ice just in these few areas? Science team member Jason Cook says it’s likely due to other, more volatile ices masking the water ice.

NASA’s Ralph instrument has previously shown Sputnik Planum is rich in other ices including nitrogen, carbon monoxide and methane.

The location of the water ice does have scientists scratching their heads. If you overlay the recently released color images with the water ice signatures, the water ice sits in areas that are bright red. “I’m surprised this water ice is so red,” says Silvia Protopapa, another member of the science team. “We don’t yet understand the relationship between water ice and the reddish tholin colorants on Pluto’s surface.”

The answers may still be on New Horizons. The spacecraft is still in the early phases of its data dump to Earth with all the data from its Pluto encounter. I wonder what other surprises lurk in the low-frequency radio waves making the 3.1 billion mile journey from New Horizons to Earth.

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