Strange light flashes that reflect off planet Earth have been captured by a NASA project. Now, scientists believe they may have discovered the origins: high-altitude ice crystals.
The mysterious phenomenon was imaged by the Deep Space Climate Observatory or DSCOVR of the National Oceanic and Atmospheric Administration, an Earth and space weather satellite launched back in 2015. Over a one-year period, keen observers caught hundreds of flashes of light, leading NASA scientists to a thorough probe.
Flashing Lights That Have Puzzled Carl Sagan
The EPIC instrument is a powerful camera aboard DSCOVR that takes near-hourly images of the space between the sun and our planet. Project scientist Alexander Marshak noticed the light flashes first over oceans as he went through that day’s EPIC captures.
Apparently, the reflections from the “pale blue dot” were the same ones that garnered Carl Sagan’s attention back in 1993 while he was going over Galileo spacecraft images. Galileo was investigating Jupiter yet briefly turned its tools toward the home planet, where the weird scene appeared.
The light flashes were so huge they can be seen from space, and originally scientists thought they were caused by sunlight that reflected off the ocean surface.
"Large expanses of blue ocean and apparent coastlines are present,” Sagan and his colleagues wrote in a 1993 study in Nature, “and close examination of the images shows a region of [mirror-like] reflection in ocean but not on land."
Marshak offered an explanation: sunlight touches a smooth lake or ocean portion, reflects back directly into space, and hits the camera right on. The ocean then works like a flashbulb in front of the camera.
But how would one explain spotting them on land?
In Galileo images, on the other hand, there were sparkling light flashes over land, and Marshak began getting flooded by emails from curious minds as to what could the flashes be.
“When I first saw it, I thought maybe there was some water there, or a lake the sun reflects off of. But the glint is pretty big, so it wasn’t that,” Marshak said in a statement.
The Key Is In Ice Crystals
The scientists put their thinking cap on and focused on water elsewhere in the planet: ice particles situated high up in the atmosphere.
They conducted new experiments and, in a new paper, confirmed the source of the remote flashes. They tested their idea by taking an inventory of sun glints hitting land in the satellite images, where the bursts took place 866 times from June 2015 to August last year.
If reflected sunlight is the cause, the flashes would be restricted to certain spots where the angle between Earth and the sun is equivalent to the angle between the space vehicle and the planet. This way, the spacecraft would pick up the reflected light.
As they suspected, the flashes happened only at locations and times on Earth where the angles matched.
Next, they plotted the angle of light to see if the glints reflected off ice particles that horizontally floated up there in the atmosphere.
The team finally showed that the light likely wasn’t emanating from the planet, as whenever they occurred, there were cirrus clouds hovering around. These clouds are made up of, what else, ice crystals.
The scientists are studying how commonly the horizontal ice crystals manifested, and if they are typical enough to notably impact the amount of sunlight passing through Earth’s atmosphere. They could potentially be integrated into computer models of how much heat the Earth receives and sees leaving.
The findings have been discussed in the journal Geophysical Research Letters and EPIC images can be found here.