The first crewed mission to Pluto is going to be a master class in homesickness. After traveling 4.7 billion miles to the icy rock, those future pioneers—breathing bottled air, bundled in awkward space clothes, buoyant in low gravity—will have little to remind them of home. But upon landing, they might just ease their pangs of longing by gazing up into the dwarf planet's sky—which, scientists now know, is blue just like Earth's.
NASA broke the news today by sharing the above photo of Pluto's cerulean halo, taken in July by the New Horizons spacecraft.
Like Earth's heavenly hue, Pluto's blue sky is caused by tiny, sunlight-scattering particles in the atmosphere. Those particles probably begin as molecular nitrogen (which Pluto is constantly emitting) and other trace gases. The sun's ultraviolet rays break down and ionize these molecules, which then combine into larger (though still microscopic) particles.
The particles aren't blue themselves; they're reddish to grey, and are heavy enough that they eventually fall back down to the dwarf planet's surface.
But wait! There's more! See those conveniently-colored blue blobs on the above close-up? Those are frozen water, confirmed by combining spectral infrared and visible light data taken by two of New Horizons' imagers. What's compelling to scientists (besides the fact that water exists) is why it appears where it does: on rocky outcrops near craters, and between mountains.
Another mystery is the water's hue, which appears bright red in color imagery. The New Horizons team thinks this indicates some sort of relationship between the surface ice and those atmospheric particles responsible for Pluto's blue sky.
Maybe I'm biased, but those pretty skies and chunks of water make Pluto seem like a pretty good setting for Hollywood's next lost-in-space blockbuster. Damon, you up for getting stranded on yet another world?
