Illustration of Plasmasphere around Earth (IMAGE) NASA/Goddard Space Flight Center Caption The two populations of hiss, low and high frequency, inhabit two separate regions in near-Earth space. Credit NASA's Goddard Space Flight Center/Mary Pat Hrybyk-Keith 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.