Comet Hartley 2 is in a hyperactive class of its own compared to other comets visited by spacecraft, says a new study. New, in-depth analysis of the images and data taken during the flyby of the comet last fall by NASA’s Deep Impact spacecraft confirms that carbon dioxide is the volatile fuel for Hartley 2’s ice-spewing jets and provides new twists in the unfolding story of this small, but dynamic comet.