About 25 years ago, astronomer Carl Sagan and his team noticed something a little odd about images coming back from the Galileo spacecraft: They showed glints of light seemingly coming from Earth.
Now, a NASA study appears to have cracked the source of the mystery: floating ice crystals. In a news release, astronomers explain that the mysterious flashes were spotted again in images shot by a weather satellite launched by the National Oceanic and Atmospheric Administration in 2015.
Sagan's team saw the flashes only over oceans, which could theoretically be explained by the sun reflecting off smooth patches of water. The problem? "We found quite a few very bright flashes over land as well," says Alexander Marshak of NASA's Goddard Space Flight Center.
Marshak's team then theorized that a different form of water might be responsible for the flashes—"flecks of high-flying ice crystals in the atmosphere glinting in the sun," as Live Science puts it.
They pored over data from all 866 flashes found in the images from the Deep Space Climate Observatory, or DSCOVR, and concluded that chunks of ice floating horizontally in the atmosphere were the culprit.
One telltale clue, per Tech Times: The scientists found that the flashes seemed to occur around high-floating cirrus clouds, and those clouds are made up of ice crystals.
"The source of the flashes is definitely not on the ground," says Marshak, per the release. (In another new study, scientists say that the asteroid that wiped out dinosaurs hit in the worst spot possible.)
This article originally appeared on Newser: Flashes Spotted by Carl Sagan Are Finally Explained