Comet Hartley 2
Discovered by Malcolm Hartley
Date of Discovery 15 March 1986

Comet Hartley 2, designated as 103P/Hartley by the Minor Planet Center, is a small periodic comet with an orbital period of 6.46 years. It was discovered by Malcolm Hartley in 1986 at the Schmidt Telescope Unit, Siding Spring Observatory, Australia. Its diameter is estimated to be 1.2 to 1.6 kilometres (0.75 to 0.99 mi).

Hartley 2 was the target of a flyby of the Deep Impact spacecraft, as part of the EPOXI mission, on 4 November 2010, which was able to approach within 700 kilometers (430 mi) of Hartley 2 as part of its extended mission. As of November 2010 Hartley 2 is the smallest comet which has been visited. It is the fifth comet visited by spacecraft, and the second comet visited by the Deep Impact spacecraft, which first visited comet Tempel 1 on 4 July 2005.