[1] It was discovered by Malcolm Hartley in 1986 at the Schmidt Telescope Unit, Siding Spring Observatory, Australia.

[14] Observation by the Spitzer Space Telescope in August 2008 showed the comet nucleus to have a radius of 0.57 ± 0.08 kilometers (0.354 ± 0.050 mi) and a low albedo of 0.028.

[9] Barring a catastrophic breakup or major splitting event, the comet should be able to survive up to another 100 apparitions (~700 years) at its current rate of mass loss.

[9] Radar observations by the Arecibo Observatory during the comet's 2010 apparition revealed that the nucleus is highly elongated and rotates over an 18-hour period.

Michael A'Hearn, the science team leader for the EPOXI mission, stated "Early observations of the comet show that, for the first time, we may be able to connect activity to individual features on the nucleus".

[11] A University of Maryland-led study published in 17 June issue of the journal Science described an analysis of the mission.

Key findings from the mission include: (1) the smooth, relatively inactive waist of the peanut shaped comet has probably been re-deposited; (2) Hartley 2 spins around one axis, but also tumbles around a different axis; and (3) on its larger, rougher ends, the comet's surface contains glittering, blocky objects that are about 165 feet (50 meters) high and 260 feet (79 meters) wide (as big as a 16-story building).

[19][20] The Deep Impact spacecraft, which had previously photographed Comet Tempel 1, was reused by NASA to study Hartley 2.

However, Boethin had not been observed since 1986, and its orbit could not be calculated with sufficient precision to permit a flyby, so NASA re-targeted the spacecraft toward Hartley 2 instead.

"[22] NASA's scientists reported that the rays coming off the rough ends consist of hundreds of tons of fluffy ice and dust chunks – the largest particles are of golf ball to basketball-size – and they are ejected by jets of carbon dioxide.