When the New Horizons spacecraft zipped past Pluto in July 2015, it revealed a bizarre world full of surprises. Giant plains of nitrogen ice, isolated mountains of what may be water ice frozen so cold it's harder than rock on Earth, and even very thin haze layers suspended in the very thin atmosphere.
One odd thing planetary scientists noticed was that some of those mountains were dark at lower elevations but very bright at their peaks, as if they were snow or frost capped. In fact, they resembled nothing so much as alpine peaks on Earth!
Of all the things to expect when seeing Pluto up close for the first time, hints of home were way down on the list.
But the resemblance is superficial. Those peaks aren't covered in water snow or frost. It's frozen methane.
That was unexpected, and explaining it is a bit difficult. But some scientists have come up with a reason this may be happening, and it relies on an important fact: Pluto works very differently than our own warm world in some specific ways.
Pluto’s dark Cthulhu region (left) has frost-covered mountains (middle, zoomed from yellow rectangle) that look a lot like the Earth’s ...