One million miles from Earth, a NASA camera is capturing unexpected flashes of light reflecting off our planet.

The homeward-facing instrument on NOAA’s Deep Space Climate Observatory, or DSCOVR, launched in 2015, caught hundreds of these flashes over the span of a year. 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. In a new study, scientists deciphered the tiny cause to the big reflections: high-altitude, horizontally oriented ice crystals.

“The source of the flashes is definitely not on the ground,” said Alexander Marshak, DSCOVR deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new study in Geophysical Research Letters, a journal of the American Geophysical Union. “It’s definitely ice, and most likely solar reflection off of horizontally oriented particles.”

Detecting glints like this from much farther away could be used by other spacecraft to study exoplanets, Marshak said. He is now investigating how common these horizontal ice particles are and whether they’re common enough to have a measureable impact on how much sunlight passes through the atmosphere. If so, it’s a feature that could be incorporated into computer models of how much heat is reaching and leaving Earth, he said.

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