Comet Hartley 2
Comet 103 P/Hartley 2, discovered in 1986, is a Jupiter-family comet with an orbital period of 6.46 years and a semimajor axis of 3.46 AU. Its perihelion distance to the Sun is 1.05 AU, close to Earth’s orbit. In 2010, the comet approached the Earth to a distance of 0.12 AU. Radar observations revealed an elongated shape and measured a rotation period of 18 h. On November 2010, the comet was visited by the Deep Impact spacecraft, renamed Epoxi, after its flyby of comet Tempel 1. Epoxi approached the comet at a distance of 700 km, measured its maximum size (2.25 km), and revealed an unexpected activity. In 2011, the Herschel space observatory measured heavy water HDO in the coma and inferred a D/H ratio close to the terrestrial value. This result suggests that the ocean water might come, at least partly, from Jupiter-family comets.