Cirrus Clouds (IMAGE) NASA/Goddard Space Flight Center Caption Typically found at heights greater than 20,000 feet, cirrus clouds are composed of ice crystals, which IceCube will measure as the Science Mission Directorate's first Earth-1 CubeSat mission. Credit NOAA Photo Library Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.