Swinging inside the orbit of Mercury, on April 20th periodic comet Encke encountered a blast from the Sun in the form of a Coronal Mass Ejection (CME).
When CMEs, enormous clouds of energetic particles ejected from the Sun, slam into Earth's magnetosphere, they often trigger auroral displays.
But in this case, the collison carried the tail of the comet away.
The tail was likely ripped off by interacting magnetic fields rather than the mechanical pressure of the collision.