Humming on red planet: NASA's Mars helicopter heard humming on red planet

First came to the amazing pictures, then the video. Now NASA is sharing sounds of its little helicopter humming through the thin Martian air. NASA's Jet Propulsion Laboratory in California released this first-ever audio Friday, just before Ingenuity was set to soar on its fifth test flight. The low hum from the helicopter blades spinning at more than 2,500 revolutions per minute is barely audible. It almost sounds like a low-pitched, far-away mosquito or other flying insects. Scientists isolated the sound of the whirring blades and magnified it, making it easier to hear. The sound was recorded during the helicopter's fourth test flight on April 30.