In 1993, the Galileo spacecraft was launched to study Jupiter. While in space, Galileo turned around and took several images and measurements of Earth at Carl Sagan’s request. These data were used as a control group to establish a baseline for what satellite readings of life-sustaining planets might look like. Interestingly, Sagan and his colleagues detected several anomalies in the images: bright flashes of light in Earth’s atmosphere that had no apparent origin.
The researchers initially thought these might be due to light reflecting off of the Earth’s oceans, but images of similar flashes of light were later observed in areas of the atmosphere over land. The source of the flashes remained a mystery for decades, but now NASA scientists believe they have this mystery solved.
According to a NASA press release, images captured by NASA’s Earth Polychromatic Imaging Camera (EPIC) flying aboard NOAA’s Deep Space Climate Observatory satellite (DSCOVR), prove that the mysterious flashes of light seen by Sagan and company have a rather simple scientific explanation: sunlight and ice.
Scientists at NASA’s Goddard Space Flight Center used powerful spectrographic imaging software to comb through images of 866 such flashes while plotting their locations against the angle of the sun relative to the flashes. According to their data published in the recent issue of Geophysical Letters, the researchers found that the angles and spectra of light suggest that the flashes are the result of sunlight reflecting off of ice particles suspended in Earth’s lower atmosphere:
We conjectured glints off horizontally oriented ice platelets floating in cirrus clouds as the physical origin, but lacked proof. Serendipitously, not only has [DSCOVR] detected the bright flashes over land but it has also accorded us an opportunity to prove that glint off horizontally floating ice platelets in clouds is indeed the physical origin of distant flashes.
Yeah, I know. I was hoping for something stranger myself. However, NASA scientists now have one more sign to look for when scanning data of distant planets that could aid in detecting exoplanet atmospheres. Any similar glints of light could suggest atmospheres which contain ice and therefore might have suitable environments for life. See? There’s always a silver lining.