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GREEN AURORAS ON MARS: One day, when humans go to Mars, they might find that the Red Planet has green skies. NASA's MAVEN spacecraft has discovered widespread auroras on Mars--and not where researchers expected them to be. Get the full story from Science@NASA.
RED AURORAS ON EARTH: Most auroras are green. On May 10th, Alan Dyer witnessed an unusual display of red. "From my observing site near Gleichen, Alberta, the northern sky had a diffuse glow of normal green aurora," reports Dyer. "But overhead, the aurora took the form of a red arc across the sky." He captured the phenomenon in this 40 minute star-trailed exposure:
Red auroras are not fully understood. They occur some 300 to 500 km above Earth's surface, much higher than ordinary green auroras. Some researchers believe the red lights are linked to low energy electrons from the sun, which move too slowly to penetrate deeply into the atmosphere. When such electrons recombine with oxygen ions in the upper atmosphere, red photons are emitted. At present, space weather forecasters cannot predict when this will occur.