A main ingredient to a comets core is dry ice.
As it gets closer to the sun the ice sublimates into the vacuum of space.
Putting dry ice into a shallow pool of water will produce a similar reaction.
The dry ice turns into vapor and creates jets of gas which propel the particles across the surface of the water.
Episode inspired by "Icy Bodies" exhibit at the Exploratorium in San Francisco.
Special thanks to Robert Shaver for sharing this exhibit in the comments section.
Music by: Paul Dateh
In Association with PBS Digital Studios