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Texas sized mystery solved?

Charon, Pluto's largest moon, has reddish colouring at its poles. Could hydrocarbons be the source of the 'staining' of this enigmatic distant planet?
This article appeared in Vol. 13, No. 4 - 2016

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Scientists at NASA are reporting that they have a solution to the mysterious red colouration observed at the polar regions of Pluto’s moon Charon. And the cause could be something very close to our hearts, hydrocarbons.

According to co-investigators on the New Horizons program, Charon’s polar colouring comes from Pluto itself - as methane gas escapes from Pluto’s atmosphere it becomes “trapped” by the moon’s gravity and freezes to the cold, icy surface at Charon’s pole. This is followed by chemical processing by ultraviolet light from the sun that transforms the methane into heavier hydrocarbons and eventually into reddish organic materials called tholins.

The New Horizons team combined analyses from detailed Charon images with computer models of how ice evolves on Charon’s poles and determined that conditions on the Texas-sized moon were cold enough to freeze methane gas into a solid - Charon’s 248-year orbit around the sun creates some extreme weather at the poles, where 100 years of continuous sunlight alternates with another century of continuous darkness and surface temperatures can dip to -430°F/-257°C.

“The methane molecules bounce around on Charon's surface until they either escape back into space or land on the cold pole, where they freeze solid, forming a thin coating of methane ice that lasts until sunlight comes back in the spring,” said Will Grundy, New Horizons co-investigator, Lowell Observatory, Flagstaff, Arizona. But while the methane ice quickly sublimates away, the heavier hydrocarbons created from it remain on the surface.

Sunlight further irradiates those leftovers into reddish tholins that have slowly accumulated on Charon’s poles over millions of years. New Horizons’ observations of Charon’s other pole, currently in winter darkness – and seen by New Horizons only by light reflecting from Pluto, or “Pluto-shine” – confirmed that the same activity was occurring at both poles.

You can find out more about the New Horizons mission by following the links below. 

If you are interested in finding out more about other natural methane occurrences, a bit closer to home - let's face it despite the best efforts of Elon Musk and SpaceX, a trip to Pluto is not a realistic probability in the near future - you could do no worse than reading our excellent Collection of articles on gas hydrates - Link.

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