The Aeronomy of Ice in the Mesosphere (AIM or Explorer 90) was a NASA satellite launched in 2007 to conduct a planned 26-month study of noctilucent clouds (NLCs).

This connection is important because a significant variability in the yearly number of noctilucent ("glow in the dark") clouds (NLCs), one manifestation of PMCs, has been suggested as an indicator of global change.

The AIM scientific objectives will be achieved by measuring near simultaneous PMC abundances, PMC spatial distributions, cloud particle size distributions, gravity wave activity, cosmic dust influx to the atmosphere needed to study the role of these particles as nucleation sites and precise, vertical profile measurements of temperature, H2O, OH, CH4, O3, CO2, NO, and aerosols.

Ball Aerospace & Technologies Corporation constructed the spacecraft bus and GATS, Inc., Newport News, Virginia, led the data management effort.

[6] The AIM satellite is a 197 kg (434 lb), 1.4 × 1.1 m (4 ft 7 in × 3 ft 7 in) spacecraft, powered by two solar panels, carrying three instruments:[7] On 25 April 2007, AIM was launched into a circular 550 km (340 mi) 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).