Spacecraft Deep Impact is ready to make its closest approach to comet Hartley 2 and photogragh the results, NASA's Jet Propulsion Loboratory (JPL) said on Wednesday.

NASA's Deep Impact spacecraft shows the first of more than 64,000 images it's expected to take of Comet Hartley 2 (shown top center) in this handout image taken on September 5, 2010 and released on September 8. The spacecraft, now on an extended mission known as EPOXI, has an appointment with the comet on November 4, 2010.  (Xinhua/Reuters File Photo)

That will mark only the fifth time a comet has been photographed up close, and the first time two comets have been imaged by the same instruments and same spatial resolution, the JPL said.

Deep Impact fired a probe into comet Tempel 1 on July, 4, 2005, and photographed the results.

If all goes as planned on Thursday, Deep Impact will swoop to within 434 miles (about 694 km) of Hartley 2, close enough to image the solid, central part of the comet, known as its nucleus.

Hartley 2, which was discovered in 1986 by English astronomer Malcolm Hartley, is thought to be between 3/4 of a mile (1.6 km) and a mile in diameter.

The flyby is eagerly anticipated by scientists, who say Hartley 2 is releasing almost the same amount of gas and dust into the surrounding environment as Tempel 1, though it is only one-seventh the size.

The emissions "can act as thrusters and actually make small changes to the comet's orbit around the sun," Mike A'Hearn of the University of Maryland, the principal investigator on the project, said in a statement.

Since sending an impactor into Tempel I more than five years ago, Deep Impact has been used to search for possible planets orbiting distant stars -- a mission dubbed Extrasolar Planet Observations and Characterization (EPOCh).

That acronym was combined with Deep Impact Extended Investigation (DIXI), yielding the mission's current name: EPOXI.

"We are really looking forward to this because the comet has shown so many surprises, both in the data from EPOXI and the data from our many collaborators, over the last several months," A'Hearn said.

VietNamNet/Xinhuanet