Washington: The Deep Impact spacecraft Thursday passed within 700 km of comet Hartley 2 at a speed of 43,000 km per hour, in what astronomers said was the best extended view yet at that class of objects in the solar system.
The mission, dubbed Epoxi, is capturing high-resolution images of the comet`s nucleus using two telescopes with digital cameras and an infrared spectrometer.
The first close-ups of the comet were relayed from Deep Impact to NASA within an hour, but scientists said it would take months to comb through all the data.
Initial photos showed an oblong object resembling a bowling pin with two rocky ends and a smooth, narrower middle.
"The stunning new images returned of the comet as it zoomed past the spacecraft at a relative speed of more than (43,450 km per hour) are awe inspiring," NASA Administrator Charlie Bolden said.
"The images taken and other science collected should help reveal new insights into the origins of our solar system as scientists pore over them in the months and years to come."
Composed of ice, dust and gases, comets offer windows on the formation of the solar system, because they are believed to be leftover building blocks of the early solar system that may have brought water and other organic compounds to Earth.
Scientists have previously captured close images of four other comets, but never one with such a small nucleus, and astronomers hope that Hartley 2 will provide new details about the composition of comets and the formation of the solar system.
"We`re going to see something that no one else in the history of humankind has seen," Ed Weiler, head of NASA`s science missions, said Thursday.
"What you saw today wasn`t virtual, it wasn`t a simulation - it was real."
University of Maryland scientist Michael A`Hearn noted that the first glimpse of Hartley 2 had already given astronomers a clearer understanding of the jets of gas that emanate out of comets.
They appear to come only from the bumpy ends of the nucleus, not from the smooth middle, and to come from frozen carbon dioxide, known as dry ice, inside the nucleus.
"Early observations of the comet show that, for the first time, we may be able to connect activity to individual features on the nucleus," he said. "We certainly have our hands full. The images are full of great cometary data, and that`s what we hoped for."
Deep Impact was reassigned to the Hartley 2 flyby after completing its first mission in 2005, delivering a probe to crash into the comet Tempel 1, in the first such look at the inner material of a comet.
The mother ship, however, remained in good condition, and NASA decided to repurpose the spacecraft for a look at another comet.
Hartley 2 is much smaller - with a nucleus that is about one kilometre wide - and more visible from Earth than Tempel 1, providing a chance to compare the celestial objects. Scientists also hope to learn about jets of material emitted by comets as they orbit the sun.
The craft will send back 64,000 pictures with its camera, which is sensitive enough to "distinguish between a car and a pickup truck" from 640 km away, mission lead engineer Amy Walsh said last week.
Deep Impact had already begun sending back images as it neared Hartley 2 and will continue to transmit even after passing close by the comet, collecting a total of 11 weeks of data.
The comet was discovered by Australian astronomer Malcolm Hartley in 1986 during a survey of the southern sky, and he was present at NASA Jet Propulsion Laboratory in California to watch the flyby.