Nearly 10 days after its Pluto fly-by, NASA's New Horizons mission has found evidence of exotic ices flowing across Pluto's surface and a surprising extended haze - a phenomenon only seen on active worlds like Earth and Mars.
"With flowing ices, exotic surface chemistry, mountain ranges and vast haze, Pluto is showing a diversity of planetary geology that is truly thrilling," said John Grunsfeld, NASA's associate administrator for the Science Mission Directorate, in a statement.
The mission found evidence of exotic ices flowing across Pluto's surface and revealing signs of recent geologic activity, something scientists hoped to find but did not 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.
Additionally, new data indicates the centre of Sputnik Planum is rich in nitrogen, carbon monoxide and methane ices.
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The Long Range Reconnaissance Imager (LORRI) on board New Horizons also captured sunlight streaming through the atmosphere and revealing hazes as high as 130 kms above Pluto's surface.
A preliminary analysis of the image shows two distinct layers of haze -- one about 80 kms above the surface and the other at an altitude of about 50 kms.
"The hazes detected in this image are a key element in creating the complex hydrocarbon compounds that give Pluto's surface its reddish hue," added Michael Summers, New Horizons co-investigator at George Mason University in Fairfax, 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.
Scientists previously had calculated temperatures would be too warm for hazes to form at altitudes higher than 30 kms above Pluto's surface.
"We are going to need some new ideas to figure out what's going on," Summers said.
The New Horizons mission will continue to send data stored in its onboard recorders back to Earth through late 2016.
The spacecraft currently is 12.2 million kms beyond Pluto, healthy and flying deeper into the Kuiper Belt.