NASA spacecraft flies past Comet Hartley 2, sends back spectacular photos (UPDATED)

Editor's note...
  • Posted at 11:40 AM, 11/04/10: NASA spacecraft flies pas Comet Hartley 2
  • Updated at 05:55 PM, 11/04/10: Scientists thrilled with comet flyby; will take months to analyze torrent of data
CBS News

A recycled NASA spacecraft that flew past comet Tempel 1 in 2005, blasting out a crater with a small sub-satellite, streaked past a second comet Thursday, passing within 435 miles of Comet Hartley 2 and beaming back spectacular pictures revealing a strange, peanut-shaped nucleus spewing multiple jets of icy debris.

Three photos of the nucleus of Comet Hartley 2, imaged by NASA's EPOXI/Deep Impact spacecraft during a 435-mile flyby Thursday. (Photos: University of Maryland)
The Deep Impact spacecraft, the centerpiece of a re-purposed mission known by the acronym EPOXI, flew past Hartley 2 at more than seven miles per second, or 27,000 mph, making its closest approach at 10 a.m. EDT.

A few moments later, the spacecraft re-oriented itself and aimed its high-gain antenna back toward Earth to begin relaying stored pictures and telemetry. The first images sent back were shot with a medium-resolution camera, starting 18 hours before close approach. As subsequent images came in from deep space, the comet grew in size and clarity on computer monitors in the control room at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Finally, when an initial set of five close-up images came in, engineers and scientist in the control room burst into applause.

The images showed a strangely peanut-shaped nucleus stretching about 1.2 miles from end to end with jets of debris extending away from one end and other, smaller jets at different locations around the body. The middle section of the elongated body appeared smooth and the jets appeared to originate in much rougher terrain near the ends.

Scientists already knew Hartley 2 had a dual-lobe shape based on ground-based radar images obtained earlier. But the clarity of the pictures from Deep Impact's medium-resolution camera showed a remarkable level of detail.

"It dawned on me as we were waiting for that first picture, we had no idea what we were going to see other than it was going to be a weird-shaped object," Ed Weiler, director of space science at NASA headquarters, told the EPOXI team. "That was the exploration part. Now the fun really starts. Now we've to explain what the hell we're looking at. That's the science!"

Jessica Sunshine, a project co-investigator, said Hartley 2 is the smallest of the five comets that have now been visited by spacecraft but "it's undoubtedly the most interesting and for its size, it's the most active."

"What we've been able to do with this mission is, for the first time, see jets going all the way to the surface and have a camera that's good enough to actually see the variability of the surface at the same time," she said. "What we're working on is trying to link those two, that is, how does the activity that's natural for the comet affect its surface?"

She said the dominant geologic feature of the comet is "two rough ends and a smooth middle. I'm not sure what that makes it, but that's what it is."

"We have rough terrain where the jets are and in many cases they seem to be correlated to specific topographic features," she said. "And the middle, we think, is fine-grained material that has been redistributed across the comet and collected in a topographic low. So you get fine, smooth material in the middle."

Scientists also were intrigued by bright clumps of material that may be remnants of past jet activity and by the numerous active jets, apparently driven by sublimation of dry ice -- frozen carbon dioxide.

"We have jets in the nighttime, we have jets along the edge and we have jets in the sun," Sunshine said. "This is probably as good a place as any to admit we have a lot of work to do to try to understand what's going on here. But this is just spectacular."

Principal Investigator Michael A'Hearn at the University of Maryland said the primary goal of the encounter was to learn more about the evolution of the so-called "dirty snowballs," believed to have formed during the birth of the solar system 4.5 billion years ago, what causes differences in appearance and behavior and how those differences might reflect the initial composition of the solar nebula.

"What we hope to do was use the difference between a small, active comet and a large, relatively inactive comet like Tempel 1 or Borrelli, to address the question of what parts of comets are due to the recent processing, what parts tell us about the formation of the solar system four-and-a-half billion years ago," he said.

"Ultimately, what we want to use this for is to figure out how did we get here? What materials came to Earth four-and-a-half billion years ago that enabled life to exist here, what were the conditions when the planets were forming? The comets are the cores of Jupiter, Saturn, Uranus and Neptune. They have large cores that are made up of comets and the comets that didn't get captured in those planets are what are left over for us to see. So that's the ultimate goal of studying any comets."

Before Thursday's encounter, only four comets had been closely imaged by passing spacecraft: Halley, Wild 2, Borelli and Tempel 1.

"You'll notice they are very different from one another, both the overall shape and the kinds of features on the surface," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory. "Three of them are about the same size, about four miles across, Halley is about twice as big.

"What we want to understand is why these differences occur when we don't see obvious differences in the processes that should shape what we see. What we wanted to do was go to a small nucleus and Comet Hartley 2 had been identified as early as the Deep Impact prime mission as a potential target."

NASA managers initially selected a different target, but that comet apparently broke apart and disappeared. The team then shifted its focus to Hartley 2, discovered by Australian astronomer Malcolm Hartley in March 1986.

"It's a very special time for me, I never imagined 24 years ago that I'd be witnessing something like this," Hartley said during a media teleconference last month. "When I saw the comet, it was millions and millions of kilometers away, and it's only going to be about 700 kilometers away when I next see it. So I'm extremely excited and feel very privileged to be here."

Hartley was present in the control room at JPL as Deep Impact flew past at some 435 miles. The approach distance was set to maximize the science return and to ensure the spacecraft's protection from jets of carbon dioxide gas and debris.

"The closer we get to the comet, the better our image resolution, so we want to get as close as we can," said Larson. "But we're also limited by the turn rate of the spacecraft. As the comet zooms by us, we have to be able to turn fast enough to track it all the way by.

"And so at 700 kilometers, it stays well within our capability to do that. If we get too much closer than 700 kilometers, we also start getting into a denser portion of the coma that poses more threats of damage to the spacecraft due to the particles that are there."