Pluto Has Blue Skies And Red Ice, NASA Says

The distant dwarf planet just keeps surprising us.

09/10/2015 6:19 AM AEDT | Updated 15/10/2015 12:11 AM AEDT

NASA's New Horizons mission keeps revealing new surprises about Pluto.

The latest: The far-flung dwarf planet has blue skies and small patches of water ice on its surface.

"Who would have expected a blue sky in the Kuiper Belt?" Alan Stern, the mission's principal investigator, said in a written statement, referring to the belt of small bodies beyond the orbit of Neptune. "It's gorgeous."

On Earth, blue skies are the result of the scattering of sunlight by gas molecules in the atmosphere. Things are a bit different on Pluto. There, sunlight is scattered not by molecules but by a haze of soot-like particles called tholins, which are created as a result of chemical reactions involving methane and nitrogen high above Pluto.

Another difference is that while Earth's sky looks blue to us most of the time, that doesn't seem to be the case on Pluto. If you stood on Pluto and looked straight up, the sky would actually appear black, the BBC reported.

"The haze is pretty thin, so you'd mostly see the color of the haze as blue sunrises and sunsets," New Horizons team member Carly Howett told the BBC.

(Story continues below photos.)

Pluto's haze layer looks blue in this picture taken by the New Horizons spacecraft. The high-altitude haze is thought to be similar to that seen at Saturn's moon Titan. The source of both hazes likely involves sunlight-initiated chemical reactions of nitrogen and methane, leading to soot-like particles (tholins) that grow as they settle toward the surface. This image was generated by software that combines information from blue, red and near-infrared images to replicate the color a human eye would perceive as closely as possible.
Regions with exposed water ice are highlighted in blue in this composite image from the New Horizons spacecraft. It combines visible imagery with infrared spectroscopy. The strongest signatures of water ice occur along Virgil Fossa, just west of Elliot crater on the left side of the inset image, and also in Viking Terra near the top of the frame. A major outcrop also occurs in Baré Montes towards the right of the image, along with numerous smaller outcrops, mostly associated with impact craters and valleys between mountains. The scene is approximately 280 miles (450 kilometers) across. Note that all surface feature names are informal.

The water ice was detected in several places on Pluto's surface, including impact craters and valleys. And if you're envisioning patches of whitish-bluish stuff like the ice seen in chilly spots on Earth, think again. Pluto's water ice is a crimson color--perhaps as a result of ice-covered tholins that fall to the surface.

"I'm surprised that this water ice is so red," Silvia Protopapa, a New Horizons science team member from the University of Maryland, College Park, said in the statement. "We don't yet understand the relationship between water ice and the reddish tholin colorants on Pluto's surface."

The New Horizons spacecraft is now 3.1 billion miles (5 billion kilometers) from Earth and is still sending photos and data back to NASA. Stay tuned for more.

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