Magazine article Science News

Flowing Ice, Haze Spotted on Pluto: Latest New Horizons Data Explain Dwarf Planet's Red Hue

Magazine article Science News

Flowing Ice, Haze Spotted on Pluto: Latest New Horizons Data Explain Dwarf Planet's Red Hue

Article excerpt

Exotic ices flow across Pluto's surface. And the dwarf planet's reddish color appears to come from a thin haze. These new finds from the New Horizons spacecraft have set scientists scrambling to construct the story of how Pluto's climate works.

A stunning image of the dwarf planet in silhouette, released July 24, reveals a layer of haze extending at least 130 kilometers above Pluto's surface. That's five times farther than predicted, Michael Summers, a New Horizons scientist at George Mason University in Fairfax, Va., said at a news conference. Still, Pluto's surface pressure has been sliced in half over the last two years, suggesting that half its atmosphere has frozen and fallen to the dwarf planet's surface.

The haze shows how the atmosphere of Pluto and its surface are connected, Summers said. The atmosphere has methane gas. When ultraviolet light from the sun interacts with methane in the upper atmosphere, more-complex hydrocarbon gases, such as ethylene and acetylene, are produced. These gases fall to lower, colder parts of Pluto's atmosphere and condense into ice particles. UV light converts these icy hazes to hydrocarbons called tholins, which fall to the ground and give the planet its dark patches. "We think this is how Pluto's surface got its reddish hue," Summers said.

With the latest data, researchers can tie the colors they see to the composition of the dwarf planet's surface, explained New Horizons deputy project scientist Cathy Olkin of the Southwest Research Institute in Boulder, Colo. Images taken as the spacecraft approached Pluto reveal banding patterns of dark and light spots that give hints of weather and seasonal patterns, which the team still doesn't fully understand. That banding pattern, Olkin noted, is abruptly interrupted by Pluto's bright heart-shaped region, which has its own story to tell. …

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