A high-resolution camera on NASA's EPOXI spacecraft captured stunning images of part of the nucleus of comet Hartley 2. The sun is illuminating the nucleus from the right, and a distinct cloud of individual particles is visible. This image was obtained on Nov. 4, 2010, the day the EPOXI mission spacecraft made its closest approach to the comet.
Infrared scans of comet Hartley 2 by NASA's EPOXI mission spacecraft show carbon dioxide, dust, and ice being distributed in a similar way and emanating from apparently the same locations on the nucleus. Water vapor, however, has a different distribution implying a different source region and process.
At the active end of the nucleus of comet Hartley 2, icy particles spew from the surface. Most of these particles are traveling with the nucleus. They are fluffy "snowballs" about 3 centimeters to 30 centimeters (1 inch to 1 foot) across.
This zoomed-in image from the High-Resolution Instrument on NASA's EPOXI mission spacecraft shows the particles swirling in a "snow storm" around the nucleus of comet Hartley 2. Scientists estimate the size of the largest particles ranges from a golf ball to a basketball. They have determined these are icy particles rather than dust. The particles are believed to be very porous and fluffy.
After a cosmic chase lasting months and covering millions of miles, a comet-hunting spacecraft finally caught its icy quarry. NASA's Deep Impact probe zoomed to within 435 miles (700 kilometers) of Comet Hartley 2 at 10:01 a.m. EDT today, taking pictures all the while. The close encounter marked just the fifth time that a spacecraft has ever visited a comet.
Mission scientists hope the rendezvous reveals what Hartley 2's icy nucleus is made of. By comparing Hartley 2 to the four other comets spacecraft have visited, they're hoping to gain a better understanding of comet structure and behavior, and perhaps of the solar system's formation. "This comet is unlike any we've visited before, and we don't know what we're going to find," Mike A'Hearn of the University of Maryland, principal investigator of Deep Impact's mission, said before the encounter.
Researchers are eagerly anticipating sifting through the wealth of comet observations Deep Impact is expected to beam back to Earth. During the encounter, the spacecraft is expected to snap about 118,000 images, NASA officials said.
On June 27 of this year, Deep Impact whipped past Earth, using our planet's gravity to set it on a course for Hartley 2. The extended mission to rendezvous with Comet Hartley 2 costs about $42 million, NASA officials have said. In September, Deep Impact went into approach mode as it neared its icy target, taking pictures and gathering data to prepare for the flyby.
This artist's concept shows us the first time Deep Impact encountered a comet -- Tempel 1 in July 2005. The Deep Impact satellite is now on the EPOXI extended mission, and just encountered its next comet, Hartley 2.
Deep Impact will continue photographing Comet Hartley 2 for about three weeks as the comet speeds off into the dark reaches of space. After that point, the spacecraft's comet-watching mission will be basically over, and Deep Impact will be decommissioned after a final calibration run, NASA officials said.
The spacecraft can retire with its head held high, having delivered on two separate comet-hunting missions, mission managers said. "This is going to give us the most extensive observation of a comet to date," said Tim Larson of NASA's Jet Propulsion Laboratory. Larson is project manager of Deep Impact's mission to Hartley 2.
A NASA spacecraft has beamed back the first close-up photos from its rendezvous with a peanut-shaped comet -- revealing jets of dust and gas in a cometary snow storm.