Blue Skies and Red Ice

NASA’s New Horizons mission keeps revealing neat stuff about Pluto.

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

On Earth, blue skies are the result of the scattering of sunlight by gas molecules in the atmosphere. On Pluto, 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.

Water ice was also 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.

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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