NASA's New Horizons spacecraft has found Pluto has brilliant blue skies and a landscape of water ice.
The findings suggest haze particles surrounding the dwarf planet are likely gray or red but scatter blue light in a way that caught the New Horizons team's attention, NASA reported.
"That striking blue tint tells us about the size and composition of the haze particles," said science team researcher Carly Howett, of SwRI (Southwest Research Institute). "A blue sky often results from scattering of sunlight by very small particles. On Earth, those particles are very tiny nitrogen molecules. On Pluto they appear to be larger - but still relatively small - soot-like particles we call tholins."
Tholin particles are believed to form high in the atmosphere when sunlight ionizes nitrogen and methane molecules, allowing them to react with each other and form complex negatively and positively charged ions. When these molecules recombine they form complex macromolecules that clump together and grow to form particles. Volatile gases coat the surface of these particles with ice frost as they fall throught the atmosphere to the surface, contributing to Pluto's red coloring. The researchers also spotted a number of small regions of exposed water ice on Pluto's surface.
"Large expanses of Pluto don't show exposed water ice," said science team member Jason Cook, of SwRI, "because it's apparently masked by other, more volatile ices across most of the planet. Understanding why water appears exactly where it does, and not in other places, is a challenge that we are digging into."
The researchers were surprised to find the areas showing the most obvious water ice spectral signatures closely corresponded with red patches seen in recently taken color images.
I'm surprised that this water ice is so red," said Silvia Protopapa, a science team member from the University of Maryland, College Park. "We don't yet understand the relationship between water ice and the reddish tholin colorants on Pluto's surface."
