Destination: Earth orbit. Launch: Fall 2006. Mission: To use the Aeronomy of Ice in the Mesosphere (AIM) mission to help scientists investigate the causes of the recent rise in noctilucent (glow-in-the-dark) clouds, wispy swirls that form about 50 mi (80 km) above the surface of the earth. The presence of the clouds over the polar regions has increased markedly in recent decades, and is thought by many scientists to be related to higher concentrations of greenhouse gases in Earth's atmosphere.
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