The solar system beyond Earth is often depicted as a dark, hostile and barren place where you absolutely wouldn’t want to get stranded. But the latest results from a pair of intrepid explorers have once again confounded the expectations of planetary scientists. They reveal blue skies over Pluto and an ancient, tranquil lake on Mars that could have supported life. This time last year, our best picture of Pluto was a grey, fuzzy undistinguished blob with no redeeming features. What a difference a 15 minute fly-by makes. Since the New Horizons mission started returning data in July, we have seen amazing landscapes, including a vast and smooth icy plain bordered by jumbled blocks of ice and rock, as well as patterned ground that has been described as having a texture like a snakeskin. We have seen ripples and ridges, things that look like mosaics of plates of ice and things that look like river valleys. And now we have learnt that these features all lie below a blue sky. Does this remind you of somewhere else? We too are enveloped in a thin blue coat. The colour of our sky, and Pluto’s, is caused by the same mechanism – the scattering of light by small particles in the atmosphere, with the main constituent being nitrogen. But there the similarities end. For a start, Earth’s atmosphere is about 100,000 times as dense as Pluto’s, and its second highest component is oxygen. On Pluto, nitrogen is accompanied by methane, and it is probable that the particles which scatter light are a group of molecules called tholins. These are formed when ultraviolet radiation (from the sun) breaks up molecules (like nitrogen and methane), which then react together, producing more complex molecules. What’s really interesting about tholins (which are also present in the atmosphere of Saturn’s giant planet Titan) is that they can keep reacting with newly broken-up molecules, growing larger and larger. They may become coated with ice, and then fall as snow or hail onto Pluto’s surface. Now Pluto is far too cold for much more to happen to these molecules – but in a warmer environment, say, to take a planet at random, the Earth about 4.5 billion years ago, maybe they could be the organic seed that eventually led to biology? Unfortunately Pluto is not the best candidate for extra terrestrial life. That spot belongs to Mars.This article has been republished from TheConversation.com.