Pluto: mini-planet of blue skies and ice galore

Photos taken by the New Horizons probe reveal that Pluto has blue skies like Earth and mountains. Photo / Nasa

It turns out that Pluto might have more going for it than even the blue-sky thinking scientists of the New Horizons space mission might have figured.

Photos from the dwarf planet have revealed mountains and glacier flows and dynamic terrain galore. Now it seems that the distant world has blue skies.

The latest photos of Pluto's atmospheric haze - now in colour - show a gorgeous blue hue.

"Who would have expected a blue sky in the Kuiper Belt? It's gorgeous," said New Horizons principal investigator Alan Stern.

While the haze is probably made up of red or gray particles, the blue tint means they are small enough to scatter blue light in the same way our own sky does.

The particles are probably a bit bigger than the nitrogen that gives our sky its colour, but they are in the same ballpark.

Enter tholins - tar-like or soot-like particles formed when nitrogen and methane break apart in ultraviolet light and recombine in new, complex macromolecules.

They are responsible for the red colouring on Pluto's surface - and probably for the great red spot on its moon Charon, as well.

It's probably these particles, formed high up in Pluto's atmosphere, that create the brilliant blue scatter.

Close-up image of a region near Pluto's equator. Photo / NASA

Blue skies aren't the only cool find announced yesterday: Nasa scientists also report finding small patches of exposed water ice. There's ice all over the chilly planet, but in most places any H2O is covered up by ices made from other molecules.

Intriguingly, the team reports, the water ice seems to correspond with the parts of the planet most strongly tinted red by tholins.

They don't know why the water ice shows up on some parts of the surface and not others, but it may have to do with these exciting macromolecules.