To skywatchers, comets often appear as soft, glowing smudges drifting across the night sky – cosmic cotton balls with faint tails. But behind that fuzzy appearance are surprisingly active worlds. Scientists studying the comet 41P/Tuttle–Giacobini–Kresak with NASA’s Hubble Space Telescope have found evidence that jets of gas erupting from its surface may have slowed the comet’s spin to a stop and then restarted it in the opposite direction.