An unexpected source recently identified a global Martian dust storm. The source was an actuator, or motor, that powers a lid to a funnel that takes in samples of powdered Martian rock dropped in by Curiosity’s drill. The samples then undergo chemical analysis by the portable Sample Analysis at Mars (SAM) chemistry lab in Curiosity’s belly.
Engineers noticed the dust storm slowly reaching Curiosity through the continuous temperature readings he collected from actuator sensors. In order for SAM to work properly, its actuators need to be at -40 °C. When Martian temperatures dip below that, SAM heaters must warm up the motors to lift the funnel lid for sample drops.