Mysterious Glowing Clouds

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. Russell described the mission on Thursday at a meeting of the American Geophysical Union in Baltimore, Maryland, US.

Bigger and brighter

The clouds were first observed above polar regions in 1885 – suggesting they may have been caused by the eruption of Krakatoa two years before. But they have spread to latitudes as low as 40° in recent years. "They're also getting brighter, and each year there are more of them than in the previous year," Russell told New Scientist.