NASA’s New Horizons snapped this photo of sunlight streaming through Pluto’s haze during the spacecraft’s close approach on July 14, 2015. But, as researchers looked closer at the photo, a question emerged: Uh, what’s with that weird glowing patch in the upper right hand corner?

The glowing patch measures over 10 miles across and hovers in Pluto’s lower atmosphere. But if you were hoping we’d caught a snap of some low-flying craft paying a visit to our solar system, prepare for disappointment: Researchers think it’s probably a cloud reflecting sunlight.

A cloud is still something very exceptional when it’s over Pluto, though. This would be the first cloud spotted in photos from the New Horizons haul. Models have long suggested that conditions on Pluto would be amenable to the formation of methane clouds—this picture seems to lend credence to that hypothesis.

Source: Gizmod