APPROACHING COMET: Green comet 103P/Hartley 2 is approaching Earth for a close encounter on Oct. 20th. At that time, the comet will be only 11 million miles (0.12 AU) from our planet and should be dimly visible to the naked eye from dark sky sites. It already looks great through backyard telescopes.
NASA's Deep Impact/EPOXI spacecraft is en route to this comet for close-up studies and a daring flyby on Nov. 4th.
Periodic comet 103P/Hartley 2 is classed as a young, dwarf comet, with a nucleus roughly 1.14 kilometers across. It belongs to the Jupiter family of comets (comets with periods less than 20 years). The comet was discovered in 1986. Although it then had an orbital period of 6.3 years, an analysis of its orbit reveals the period had been longer in the recent past. During the early decades of the 20th century, the orbital period had been 9.3 years. A close approach to Jupiter in August 1947 (0.22 AU) reduced the period to 7.9 years, while another close approach during April 1971 (0.09 AU) reduced the period to 6.1 years. The comet has been seen at every return since its discovery. The 2010 return is exceptional, as the comet will pass 0.12 AU from Earth on October 20. The Deep Impact space craft will pass about 1000 kilometers from the comet on November 4.
Comet 103P/Hartley 2 will pass 0.12AU from Earth, a mere 11 million miles in October of this year. The near approach allowing even a modest comet to become quite bright. Predictions are that the comet will be brighter than 5th magnitude, easily visible to the unaided eye from a dark site.