You can see a lot from 1 million miles away. The blues, greens and browns of Earth's oceans and land masses stand out against the blackness of space as clouds move above the planet's surface.
And sometimes you see something you may not expect.
Scientists working with NASA's EPIC camera on the Deep Space Climate Observatory spacecraft (DSCOVR), located about 1 million miles from Earth, have caught sight of hundreds of mysterious flashes of light reflecting off our planet over the course of a year.
What could they be? Reflections of sunlight glinting off oceans? A really, really annoying guy with a flashlight? Aliens?
In reality, the flashes are likely coming from ice crystals high up in Earth's atmosphere, but it took scientists a fair bit of observation to figure that out.
To solve the mystery, researchers started digging through old DSCOVR photos to try to figure out what the flashes could be, and they came across something interesting in the process: This isn't the first time a spacecraft has spotted these flashes of light.
Famed astronomer and science communicator Carl Sagan actually saw bright flashes like those seen by DSCOVR in photos taken of Earth by the Galileo spacecraft, which explored Jupiter in the 1990s.
Initially, Sagan thought those flashes were reflective bits of the ocean, but the team of DSCOVR researchers saw the flashes over land as well, meaning that it couldn't just be a water-based phenomenon.
The scientists landed on the ice crystal explanation after realizing that the flashes were coming from a high altitude and couldn't be caused by lightning due to the limited spots on the globe where they appeared.
Image: NASA's Goddard Space Flight Center
DSCOVR launched to space in 2015, and since that time, the spacecraft has taken hundreds of photos of the full sunlit side of the Earth, allowing researchers to see more than 800 of these flashes of light.
“The source of the flashes is definitely not on the ground," Alexander Marshak, DSCOVR scientist and co-author of a new study about the flashes in the journal Geophysical Research Letters, said in a statement. "It’s definitely ice, and most likely solar reflection off of horizontally oriented particles."
One day, these glints could be used to detect ice crystals and other atmospheric phenomenon on alien worlds hundreds of light-years from Earth. For now, though, scientists are going to keep using DSCOVR and other tools to study the glints at close-range.