Space agency's orbiting camera captures 'unexpected flashes of light' reflecting off our planet
Hundreds of large flashes have been filmed reflecting off our planet, and they've helped NASA solve a mystery that stumped the likes of Carl Sagan more than two decades ago.
These flashes are so large, you can see them from space, and they were originally thought to be caused by sunlight reflecting off the surface of the ocean. But then NASA started spotting them on land, and no one could say why.
Since June 2015 the Deep Space Climate Observatory (DSCOVR) satellite has been floating about a million miles away between the Earth and the Sun. On that satellite, which was developed by the National Oceanic and Atmospheric Administration in the US, NASA's Earth Polychromatic Imaging Camera (EPIC) instrument has been snapping pictures of our planet about once every hour. In some of those shots, strange flashes have been appearing all over the planet. Researchers now think they know what they are.
While radiation from secret labs, glints of gold from lost cities or flashes from freak weather events would certainly make for a more dramatic story, the NASA researchers have come to a different conclusion about the flashes, 866 of which have were found between DSCOVR's launch and August 2016. They are ice crystals, likely floating horizontally as high as five miles in the air.
Initially, researchers thought the flashes could simply have been sunlight bouncing off bodies of water, above which the flashes were first spotted. Upon closer investigation, however, they found the flashes over land as well – and the size of the flash was too big to be explained by the presence of a lake or other body of water. Ice was the next logical guess.
The video below goes into more detail about the find, and a paper detailing the work has been published in the journal Geophysical Research Letters.
To test their theory, the researchers reasoned that if the flashes were caused by sunlight bouncing off ice particles, then the shots would have to be occurring when DSCOVR was in such a position that sunlight would be reflected directly at it when it hit the crystals. Sure enough, the data matched, which meant the flashes were definitely reflections, not some type of weather phenomenon.
They then plotted the angles in more detail and came to the conclusion that the particles would have to be floating nearly horizontally to reflect light in the way they were.
Next, the researchers measured the height of the particles by using two channels on the EPIC instruments that can measure the height of clouds. Wherever there were flashes, there were also cirrus clouds that were three to five miles (5-8 km) high.
Interestingly, famed astronomer Carl Sagan also saw the flashes in the atmosphere in 1993 when he was analyzing images from the Galileo spacecraft, which examined the Earth during a gravity-assist swing-by before it headed out to Jupiter. "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 of the find in a paper in the journal Nature.
Now that present-day astronomers know about the ice crystals, their next step will be to classify just how common they really are and determine if they could actually be impacting Earth by blocking some of the sunlight that bathes our planet. Alexander Marshak, DSCOVR deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said that learning more about the ice particles here could also help us in our study of planets beyond our solar system.