Smashing a moon slowed down the main asteroid
Asteroid Didymos slowed its rotation after the DART probe slammed into its moon Dimorphos. The reason: the impact flattened Didymos, making it wider at the waist, like a figure skater spreading their arms. This 'spread' added 0.18 seconds to each rotation — less than an instant, but astronomers noticed it thanks to 20 years of observations.