Over the course of one year, a spacecraft observing earth spotted hundreds of mysterious 'flashes' reflecting off the surface of our planet.
The bizarre phenomenon was also noted in the 1990s by astronomer Carl Sagan who identified strange 'glints' in images from the Galileo spacecraft.
While it was initially thought that the strange flashes of light only appeared over oceans, scientists have now discovered that they could also be seen over land.
In the course of a new investigation, researchers found that the bursts likely had a surprisingly small source – tiny, horizontal ice crystals floating high in the sky.
NASA's Earth Polychromatic Imaging Camera (EPIC) aboard the NOAA's Deep Space Climate Observatory (DSCOVR) spotted 866 bursts of light over land between the launch of theobservatory in 2015 and August 2016.
According to Alexander Marshak, DSCOVR deputy project scientist, the flashes seen over the ocean might simply be the reflection of sunlight off a smooth part of an ocean or lake. However, the same could not be said for the flashes seen over land.
"We found quite a few very bright flashes over land as well,' said Marshak.
"When I first saw it I thought maybe there was some water there, or a lake the sun reflects off of."
In 1993, astronomer Carl Sagan noticed strange flashes of light showing up in images of earth snapped by the Galileo spacecraft.
The unmanned space probe had been launched four years earlier to study Jupiter and its moons, and Sagan and his team decided to take advantage of one of its flybys past earth, and scoured the data for signs of life on our own planet.
The idea was that if the data could reveal signs of life on earth from way up in space, any extraterrestrial neighbours could too, and know that our planet was inhabited.
In Galileo's images, they found large glints of light, that reflected like mirrors but these were limited only to regions of the planet covered in water.
"Large expanses of blue ocean and apparent coastlines are present, and close examination of the images shows a region of specular [mirror-like] reflection in ocean, but not on land," the team reported at the time.