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NASA's New Horizons spacecraft has discovered flowing ice and a surprising extended haze on Pluto, which show the dwarf planet to be an icy world of wonders.
"We knew that a mission to Pluto would bring some surprises, and now - 10 days after closest approach - we can say that our expectation has been more than surpassed," said John Grunsfeld, NASA's associate administrator for the Science Mission Directorate.
"With flowing ices, exotic surface chemistry, mountain ranges, and vast haze, Pluto is showing a diversity of planetary geology that is truly thrilling," said Grunsfeld.
Just seven hours after closest approach, New Horizons aimed its Long Range Reconnaissance Imager (LORRI) back at Pluto, capturing sunlight streaming through the atmosphere and showing hazes as high as 130 kilometres above Pluto's surface.
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A preliminary analysis of the image shows two distinct layers of haze - one about 80 kilometres above the surface and the other at an altitude of about 50 kilometres.
"My jaw was on the ground when I saw this first image of an alien atmosphere in the Kuiper Belt," said Alan Stern, principal investigator for New Horizons at the Southwest Research Institute (SwRI) in Boulder, Colorado.
Studying Pluto's atmosphere provides clues as to what's happening below, NASA said.
"The hazes detected in this image are a key element in creating the complex hydrocarbon compounds that give Pluto's surface its reddish hue," said Michael Summers, New Horizons co-investigator at George Mason University in Virginia.
Models suggest the hazes form when ultraviolet sunlight breaks up methane gas particles - a simple hydrocarbon in Pluto's atmosphere.
The breakdown of methane triggers the buildup of more complex hydrocarbon gases, such as ethylene and acetylene, which also were discovered in Pluto's atmosphere by New Horizons.
As these hydrocarbons fall to the lower, colder parts of the atmosphere, they condense into ice particles that create the hazes.
Ultraviolet sunlight chemically converts hazes into tholins, the dark hydrocarbons that colour Pluto's surface.
Scientists previously had calculated temperatures would be too warm for hazes to form at altitudes higher than 30 kilometres above Pluto's surface.
The New Horizons mission also found in LORRI images evidence of exotic ices flowing across Pluto's surface and showing signs of recent geologic activity, something scientists hoped to find but didn't expect.
The new images show fascinating details within the Texas-sized plain, informally named Sputnik Planum, which lies within the western half of Pluto's heart-shaped feature, known as Tombaugh Regio.
There, a sheet of ice clearly appears to have flowed - and may still be flowing - in a manner similar to glaciers on Earth, NASA said.
