Pluto has a blue sky?

Discoveries from New Horizons

Since its discovery in 1930, Pluto has been little more than a fuzzy blob on the edge of the solar system, with astronomers having little understanding of its geology or chemical composition. Up until this year our best image of Pluto was a fuzzy photo taken by Hubble in 2002 and the debate about Pluto’s planetary status was the most famous thing about it. Now all this has changed. After travelling 4.88 billion km, the New Horizons probe flew past Pluto in July, gathering data about the atmosphere, surface composition and taking photos of Pluto, with ten times better resolution than before. It will take New Horizons almost 16 months to transmit all its data back to Earth, but already fascinating discoveries have been made.

One discovery has particularly captured the public’s imagination - Pluto has a blue sky! One of the cameras on New Horizons sent back this image above, showing Pluto surrounded by a blue halo of light, much like our own sky. Scientists believe that this is caused by tholins (soot-like particles in Pluto’s atmosphere) scattering light when affected by UV rays, much in the same way that nitrogen particles scatter light in Earth’s atmosphere. These larger macromolecules are also responsible for the red colouring of some areas of Pluto, when they combine with volatile gases in the atmosphere, condense and fall on the planet’s surface.

But the similarities don’t end there. Bedrocks and hills made of frozen water, and glaciers made of nitrogen, carbon dioxide and methane have also been discovered on the planet, all contributing to a very similar geological process to that found on Earth, only with different elements. This discovery in particular has surprised scientists, as previous spectral analyses have found no evidence of water-ice on Pluto.

The recent discoveries of the New Horizons mission are fascinating, but they are only the beginning, as it will be well into next year before all the data is returned to Earth and even longer before scientists have analysed it. These discoveries demonstrate how much more there is to know about bodies on the edge of our solar system, many of which have been overlooked until now, with researchers focussing on planets much closer to home, like Saturn and Jupiter. Not only is New Horizons significant from a scientific point of view, but it has also captured the world’s imagination - inspiring a new generation of scientists and helping to gain support for even more missions to increase our understanding of the solar system.

Hannah Sanderson VII