The Aeronomy of Ice in the Mesosphere, or AIM, mission is the first detailed exploration of Earth's unique and elusive clouds that are literally on the "edge of space."
Earth's highest clouds form an icy membrane at the edge of the atmosphere. AIM's mission is to study the physical and chemical processes that give rise to these mysterious polar mesospheric clouds, or PMCs. Also known as noctilucent clouds, and night-shining clouds, PMCs form high above Earth's surface, and can only be seen near twilight. They have been spotted for over a century during summer months, usually at high latitudes near the North and South Poles. However, in recent years, these clouds are being seen more frequently at lower latitudes.
Launched on April 25, 2007, AIM orbits around Earth in a near-circular, sun-synchronous orbit, which is a low-altitude orbit that passes over any given point on Earth at approximately the same local time. At an altitude of some 370 miles, AIM can look down on the polar mesospheric clouds from above. The primary goal of the mission is to determine why these night-shining clouds form. They are of special interest to scientists because the increased occurrence may be related to climate change. By measuring the thermal, chemical, and other properties of the environment in which the mysterious clouds form, AIM provides researchers with a foundation for the study of long-term variations in the mesosphere and its relationship to global climate change. In addition to measuring environmental conditions, the AIM mission collects data on cloud abundance, how the clouds are distributed, and the size of ice particles within them.
In over a decade since its launch, AIM’s observations have led to more than 200 papers on Earth’s upper atmosphere. Some key scientific discoveries, include: Showing that noctilucent cloud numbers have been steadily increasing over the past decade, despite the sun’s regular changes in activity; increases in water vapor, a greenhouse gas, and decreasing upper-atmosphere temperatures — a side effect of warming near the surface -- may be contributing to the increased presence of PMCs; ice crystals in noctilucent clouds form on a tiny microparticles created when meteors burn up in Earth’s atmosphere; helping scientists track how heat moves in the upper atmosphere, showing that heating in the mesosphere is more likely linked to circulation in the atmosphere rather than direct heating from the sun.