Glowing, silvery blue clouds that have been spreading around the world and brightening mysteriously in recent years will soon be studied in unprecedented detail by a NASA spacecraft.
The Aeronomy of Ice in the Mesosphere (AIM) mission will be the first satellite dedicated to studying this enigmatic phenomenon. Due to launch in late 2006, it should reveal whether the clouds are caused by global warming, as many scientists believe.
Noctilucent” clouds, which glow at night, form in the upper atmosphere, at an altitude of about 80 kilometres, and their glow can be seen just after sunset or just before sunrise. “Even though the Sun’s gone down and you’re in darkness, the clouds are so high up, the Sun is still illuminating them,” explains AIM principal investigator James Russell at Hampton University in Virginia, US.
… As yet, it is not clear what the source of the particles that “seed” the clouds is. The clouds form during the local summer months, when the pole is bathed in perpetual sunlight. So one possibility is that warm air rising above the pole could carry dust upwards from lower atmospheric altitudes, onto which water can condense.
But the dust could also have a cosmic source, dropping into the atmosphere from space. “It may be there’s a constant supply of particles but a changing temperature and water environment makes the conditions right to grow ice particles,” says Russell. – newsci