The Cloud Imaging and Particle Size experiment on NASA’s Aeronomy of Ice in the Mesosphere satellite observes PMCs about ten times brighter than usual over Scandanvia the day after launch of STS-135. Water vapor exhaust from the shuttle and other rockets may have led to significant PMC production of the past three decades, complicating the use of PMC occurrence as an indicator of upper atmospheric climate change. (Photo by U.S. Naval Research Laboratory)