the plumes of ash propelled into the sky during that eruption. But the clouds have persisted long after the effects of Krakatoa were felt. These days, some scientists think they are caused by space dust, while others believe that modern-day PMC's are indicators of changing climate of Earth. One thing is for certain: PMC's are shaped by the meteorology of the mesosphere, which does appear to be changing. Spacecraft The AIM satellite is a , spacecraft, powered by two solar panels, carrying three instruments: Instruments Launch On 25 April 2007, AIM was launched into a circular Sun-synchronous orbit by a Pegasus-XL launch vehicle, which was air-launched from the Lockheed L-1011 Stargazer aircraft operated by Orbital Sciences Corporation (OSC). See also Aeronomy Explorer program References External links AIM home SOFIE Instrument and science description, view or download data AIM Mission Profile by NASA Taking AIM at Night-Shining Clouds: 10 Years, 10 Science Highlights Earth observation satellites of the United States NASA satellites NASA satellites orbiting Earth Spacecraft launched in 2007 Explorers Program Spacecraft launched by Pegasus rockets Geospace monitoring satellites