PICTURES: Comet Hartley 2 Seen Close-Up by NASA EPOXI Mission

Photo: NASA Mission Successfully Flies by Comet Hartley 2PlayNASA/JPL-Caltech/UMD
WATCH Historic View of a Comet

Thirteen million miles out in space, a NASA probe called Deep Impact has flown within 435 miles of Comet Hartley 2, and the early pictures are a sight to behold.

This is only the fifth time a spacecraft has ever come close enough to a comet to take pictures. What you see is not the standard image of a long, filmy tail; Hartley 2 is more than 100 million miles from the sun, and too cold to be streaming water vapor the way comets do when they come closer.

In the 1950s astronomer Fred Whipple theorized that comets were like "dirty snowballs," boulders of ice and dust that wander the outer reaches of the solar system, some of them diverted to pass close to the sun -- and within sight of earth. But their precise makeup has been hard to determine, and that is why Deep Impact was launched.

In 2005 Deep Impact passed another comet, Tempel 1, and sent a dishwasher-sized probe crashing into it. Chemical readings of the resulting blast helped flesh out Whipple's theory.

Click here to see more images of comet Hartley 2.

Truth be known, NASA believes in recycling. Deep Impact was still in fine working order, so the agency gave the mission a new name -- EPOXI -- and sent it on a long, looping path to rendezvous with Hartley 2 today.

"We are all holding our breath to see what discoveries await us in the observations near closest approach," said Michael A'Hearn of the University of Maryland, the mission's principal investigator.

Many scientists believe the first chemical building blocks of life on earth may actually have come from space -- as comets crashed into the planet not long after it formed. The early solar system, 4.6 billion years ago, was probably much more crowded than it is today, so collisions were common. Depending on whom you ask, a third of the water on earth may have come from comets that hit us back when the planet was young.

Take a look. The comet's core is about 1.4 miles long, slowly tumbling in space. The light streaks coming from it are probably jets of water vapor, where the sun's warmth has melted ice on the comet's surface.