The mysterious white flares that can be seen in the images of the DSCOVR probe were generated by ice particles in the Earth's atmosphere, reflecting the light of the Sun directly into the lens of the cameras of this spacecraft, scientists write in an article published in the journal Geophysical Research Letters.
“Initially, we thought that the flares were associated with the reflection of the Sun from the ocean, but then we found many similar white spots over land. They could not be the reflection of light from the water surface of lakes and rivers - the spots were too large. It seems that these flares do not occur on the surface of the Earth, but in its atmosphere, when light reflects off pieces of ice that are turned horizontally,”explains Alexander Marshak of NASA's Goddard Space Flight Center in Greenbelt, USA.
Launched into space in February 2015, DSCOVR is one of the latest and most advanced climate satellites from NASA and the United States Oceanic and Atmospheric Administration (NOAA). Unlike other probes of this type, it does not orbit the Earth, but is in deep space, at the point where the gravitational forces of the Earth and the Sun balance each other.
This allows him to keep track of what is happening on the planet as a whole, as well as to observe the space "weather" and the activity of the Sun. Every two hours, he receives photographs of the planet and transmits them, along with climate and other scientific data, to Earth, where they are processed by NASA specialists and NOAA climatologists.
The first photographs that the EPIC camera takes aboard the DSCOVR revealed an unusual phenomenon - many of them showed mysterious white spots and flares that were not like clouds and other potential sources of white. Over the past two years, hundreds and thousands of such flashes have been found in EPIC images, which excludes the possibility that some camera defects or cosmic rays cause them.
Marshak, one of the mission leaders, and his colleagues at NASA decided to find out where these blind spots come from. Scientists examined several hundred “tainted” photographs and analyzed where, how and when the outbreaks occurred.
As this analysis showed, flares occurred both over land and over the ocean, but at the same time they were all concentrated in that part of the planet, which at that moment was most “directly” looking at the Sun. For example, in winter, white spots most often appeared in the tropics of the southern hemisphere, in summer - in the corresponding part of the northern hemisphere, and on equinox days - at the equator.
This wandering of flares has led scientists to recall an old story that they investigated nearly 20 years ago by studying images of the Earth taken by the Galileo probe en route to Jupiter. On them, as Marshak recalls, there were also white spots, which his team considered a product of the reflection of sunlight from ice particles floating in the Earth's atmosphere.
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Then no one believed the scientists, because there were no additional photographs with similar spots, but now Marshak and his colleagues have the opportunity to test their hypothesis using DSCOVR images and a computer model of the Earth's atmosphere.
As shown by these calculations, the white spots in the photographs from the NASA climate probe and images from the Galileo are generated by ice particles in the Earth's tropospheric clouds, hovering at an altitude of five kilometers. Many microscopic pieces of ice in cirrus clouds, scientists explain, will be turned horizontally to the surface of the Earth, which will turn them into a kind of mirror that reflects the rays of the sun into space.
Such reflections, according to scientists, can be used to search for distant planets and assess their suitability for life. The light of stars, reflected from ice particles in the atmosphere of exoplanets, will be brighter than the glow of the planet itself, and in its spectrum, as scientists explain, there will be all the necessary information about the chemical composition of the atmosphere and the potential presence of life in it.