Pluto’s blue skies are completely unexpected


New Horizons has been busy sending images and data it captured on the day of its closest flyby of Pluto and as a part of that the latest set of images reveal blue skies and exposed water ice.

Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI), Boulder, Colorado, who had previously teased the announcement while delivering keynoet at University of Alberta, said “Who would have expected a blue sky in the Kuiper Belt? It’s gorgeous.”

In an explanation provided by NASA regarding the blue haze, the space agency reveals through its science team that the particles that are causing the blue haze are actually likely to be gray or red. However, it it the manner in which they scatter the blue light has gotten their attention.

Explaining further, NASA says that the blue haze is often caused by scattering of sunlight by very small particles. In case of Earth, it is caused by very tiny nitrogen molecules, but in case of Pluto, the particles are particularly large and they are what scientists call tholins.

NASA scientists first encountered tholin particles when they were investigating Saturn’s moon Titan and according to the understanding gained so far, tholin particles form high in the atmosphere, where ultraviolet sunlight breaks apart and ionizes nitrogen and methane molecules and allows them to react with one another to form more and more complex negatively and positively charged ions. When they recombine, they form very complex macromolecules and they continue to combine and grow until they become small particles; volatile gases condense and coat their surfaces with ice frost before they have time to fall through the atmosphere to the surface, where they add to Pluto’s red coloring.

Blue Sky Pluto

The New Horizons mission science team, based on data collected by the Ralph spectral composition mapper, also found numerous but small exposed regions of water ice on Pluto. While most of the Pluto’s surface do not show exposed water ice because they are covered by more volatile ices across most of the planet, there are places where water ice has been exposed.

A curious aspect of the detection is that the areas showing the most obvious water ice spectral signatures correspond to areas that are bright red in recently released color images. “I’m surprised that this water ice is so red,” says 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.”