The forecast on Pluto is clear with less than a 1 percent chance of clouds. Images from the New Horizons spacecraft show hints of what could be a few isolated clouds scattered around the dwarf planet, the first seen in otherwise clear skies.
Seven cloud candidates appear to hug the ground in images taken shortly after the probe buzzed by the planet in July 2015. Along the line where day turns to night, several isolated bright patches appear. These are consistent with clouds forming at sunset and sunrise, said mission head Alan Stern during an October 18 news conference at a meeting of the American Astronomical Society’s Division for Planetary Sciences.
If they are clouds, they’re probably made of ethane, acetylene or hydrogen cyanide, based on what researchers have learned about Pluto’s atmosphere — though they might not be clouds, just reflective splotches on the surface, Stern said. Without stereo imaging, it’s impossible to tell how high off the ground the patches are, or whether they’re in the sky at all. Since New Horizons isn’t returning to Pluto — it’s hurtling deep into the Kuiper belt — the spacecraft won’t be able to take another look at the cloud candidates and answer these questions. That will have to wait until another spacecraft goes back to orbit Pluto, Stern said.