NASA: Pluto has blue skies and water ice

NASA has released some amazing new colour shots from New Horizons’ expedition to Pluto. Not only are they spectacular, they also reveal some exciting new developments: there’s water ice, and a blue sky.

“Who would have expected a blue sky in the Kuiper Belt? It’s gorgeous,” said Alan Stern, New Horizons’ principal investigator.

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That striking blue tint tells us about the size and composition of the haze particles,” said Carly Howett, a team researcher from Southwest Research Institute (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.”

As for the water, it only appears in patches – and for the moment, it’s not entirely clear why. “Large expanses of Pluto don’t show exposed water ice,” Jason Cook of the SwRI explained, “because it’s apparently masked by other, more volatile ices across most of the planet. Understanding why water appears exactly where it does, and not in other places, is a challenge that we are digging into.”

With only a fraction of the data still downloaded from New Horizons, there could be many new discoveries to come. The previous shots from September showed the ice mountain ranges Norgay Montes and Hillary Montes rising 3,500 metres above the planet’s surface.

The images accompany a growing gallery from the most significant space mission in years. Minutes before New Horizons passed Pluto for its flyby on 4 July 2015 at 12.49 GMT, NASA released a teaser colour image of Pluto on its official Instagram account. You can see it below in all its pale-red glory, photographed some 476,000 miles away.

New Horizons successfully avoided debris that the scientists gave a one in 10,000 chance of jeopardising the mission, and returned some wonderful shots of the dwarf planet to an excited media back on Earth. As the photo below shows, emotions ran high at NASA as the first shots materialised.

And thanks to a man called Björn Jónsson, you can witness what the flyby would have looked like in this wonderful 16-second video clip. Using NASA’s own photography, and a few educated guesses, Jónsson shows what a video from the probe would have looked like.

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The time covered is 09.35 to 13.35 (closest approach occurred near 11.50). Pluto’s atmosphere is included and should be fairly realistic from about ten seconds into the animation and to the end. Earlier it is largely just guesswork that can be improved in the future once all data has been downlinked from the spacecraft. Light from Pluto’s satellite Charon illuminates Pluto’s night side but is exaggerated here, in reality it would be only barely visible or not visible at all,” he wrote.

Personally, I’m all for this kind of artistic licence when it puts me as close to the action as this video does.

It’s pretty close. This video from NASA’s Eyes on the Solar System app shows you exactly how the flyby took place, sped up to a rate of ten minutes per second.

Here are a few of the pictures that New Horizons beamed some four billion miles back to Earth, concluding a mission that started all the way back in 2006.This is Pluto itself. The dwarf planet – downgraded from fully fledged planet status after New Horizons set off – was actually larger than scientists thought, weighing in at 2,370 kilometres across, making it around two-thirds the size of Earth’s moon.

Zooming closer in, the size of Pluto wasn’t the only surprise for NASA’s scientists.

Those are mountains. And not just little ones, either – estimated to be around 11,000ft high. “They would stand up respectably against the Rocky Mountains,” said John Spencer, a planetary scientist working on the mission.

NASA suspects the mountains are composed of water ice, with a thin layer of “exotic ices” such as methane and nitrogen. “Water ice is strong enough to hold up big mountains, and that’s what we think we’re seeing here,” explained Spencer. “This is the first time we’ve seen this. The methane and nitrogen are just a coating.”

The lack of craters was also a surprise, leaving scientists speculating the dwarf planet had been recently “paved over” by geological activity – perhaps geysers of ice or cryo-volcanoes.

Finally there’s Charon – Pluto’s moon.

“Charon just blew our socks off when we had the new image today,” said Cathy Olkin, a mission scientist. “The team has just been abuzz. There is so much interesting science in this one image alone.”

What blew the scientists’ collective socks off? Well, it emerges that Charon has quite the varied terrain, with cliffs and troughs stretching for around 600 miles, which indicates some interesting geological activity. That canyon you can make out in the photo? They reckon that’s around four to six miles deep!

The best could still be yet to come. New Horizons is slowly beaming back a lot of data, so a bigger picture should emerge over the next few months.

All very well and good, but when will NASA return to the outer solar system?

All images: NASA