It was famed pop scientist Carl Sagan who first spotted the mysterious flashes that seemed to be coming from Earth’s atmosphere, and now scientists think they’ve figured out where they come from. Satellites have picked up startling images of what appears to be twinkling from Earth that scientists struggled to explain, but NASA now thinks the flashes may be caused by flecks of ice crystals high in the atmosphere that are glinting in the sun.

The flashes have been captured by the National Oceanic and Atmospheric Administration’s Deep Space Climate Observatory, or DSCOVR, which is a space weather satellite launched two years ago. The flashes happen hundreds of times in just a year, and it first caught Sagan’s attention in the 1990s when the Galileo spacecraft, which was studying Jupiter at the time, briefly turned its focus to Earth.

“Large expanses of blue ocean and apparent coastlines are present, and close examination of the images shows a region of [mirror-like] reflection in ocean but not on land,” Sagan and his colleagues wrote in a study which was published in Nature in 1993.

“NASA’s Earth Polychromatic Imaging Camera (EPIC) instrument aboard DSCOVR is taking almost-hourly images of the sunlit planet from its spot between Earth and the sun,” NASA said in a statement. “Alexander Marshak, DSCOVR deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, first noticed light flashes occasionally appearing over oceans as he looked through that day’s EPIC images.

“Investigating the flashes, Marshak and his colleagues found that similar reflections from our pale blue dot caught the attention of astronomer Carl Sagan in 1993. Sagan was looking at images taken by the Galileo spacecraft, which launched in 1989 to study Jupiter and its moons. During one if its gravitational-assist swings around Earth, Galileo turned its instruments on this planet and collected data. Sagan and his colleagues used that to test a key question: Whether spacecraft could detect signatures of life from afar.”