ISS031-E-116058 Click the photo number to access all resolutions available and the database record.
On June 13, 2012, when this image was taken from the ISS as it passed over the Tibetan Plateau, polar mesospheric clouds were also visible to aircraft flying over Canada. In addition to the still image above, the ISS crew took a time-lapse image sequence of polar mesospheric clouds several days earlier (June 5) while passing over western Asia. It is first such sequence of images of the phenomena taken from orbit.
Polar mesospheric clouds form between 76 to 85 kilometers (47 to 53 miles) above Earth’s surface when there is sufficient water vapor at these high altitudes to freeze into ice crystals. The clouds are illuminated by the Sun when it is just below the visible horizon, lending them their night-shining properties. In addition to the polar mesospheric clouds trending across the center of the image, lower layers of the atmosphere are also illuminated. The lowest layer of the atmosphere visible in this image—the stratosphere—is indicated by dim orange and red tones near the horizon.
While the exact cause for the formation of polar mesospheric clouds is still debated—dust from meteors, global warming, and rocket exhaust have all been suggested as contributors—recent research suggests that changes in atmospheric gas composition or temperature has caused the clouds to become brighter over time.
