Deep Impact - EPOXI

The EPOXI mission recycled the Deep Impact spacecraft, which had formerly visited comet Tempel 1, to visit a second comet, Hartley 2. The Nov. 4, 2010, flyby marked only the fifth time a comet had been visited by a spacecraft.

Images snapped by the spacecraft uncovered a number of new details about the hyperactive Hartley 2, including observable variations in the strength, behavior and composition of jets on the comet's surface.

November 2010: The EPOXI mission flyby reveals that comet Hartley 2's rocky ends spew out tons of golf-ball to basketball-size fluffy ice particles, while the smooth middle area is more like what was observed on comet Tempel 1 with water evaporating below the surface and percolating out through the dust.

June 2011: A science paper in the journal Science highlights some of the EPOXI mission's key findings. Including:

• Strong activity in water release and carbon dioxide-powered jets does not occur equally in the different regions of Hartley 2.
• Hartley 2 has an 'excited state of rotation' because it spins around one axis, but also tumbles around a different axis.
• On its larger, rougher ends, the comet's surface is dotted with glittering blocks that can reach approximately 165 feet (50 meters) high and 260 feet (80 meters) wide. The block-like, shiny objects, some as big as one block long and 16 stories tall, appear to be two to three times more reflective than the surface average.