Comet Show Leaves NASA Speechless

The collision of a probe from NASA’s Deep Impact spacecraft with comet Tempel 1 blew a plume of debris thousands of miles into space and provided a spectacular first glimpse of the insides of a comet -- ancient bodies that may hold the key to the origins of the solar system -- scientists said Monday.

The collision -- a carefully orchestrated dance at more than 20,000 mph intended to expose the comet’s interior -- was much larger than anyone had expected, said researchers at the Jet Propulsion Laboratory in La Canada Flintridge.

Telescopes on Earth showed that the light from the comet increased fivefold in the aftermath of the collision at 10:52 p.m. PDT Sunday before slowly fading over several hours.

“I was trying to think how to describe this, but I am just plain speechless,” said Andrew Dantzler, the director of NASA’s solar system program.

The eruption of debris from the impact was so large that principal investigator Michael A’Hearn of the University of Maryland said it could take scientists a week or more to tease out a reliable image of the impact crater from behind the smokescreen of dust and gas that obscured the comet’s surface.

By Monday morning, project scientists had had little time to analyze the information and images that were flooding into their databanks, but what they saw was drawing back the veil from the composition and structure of comets.

The high-resolution images taken before the impact show a comet surface substantially different from that of previously observed comets, such as Borrelly and Wild-2. Although the surface appears white because of reflected sunlight, it is actually jet-black. Small bright patches on the surface are most likely steep slopes that reflect more sunlight than the surrounding landscape.

The surface of Tempel 1 is littered with what appear to be impact craters -- the first time such craters have been observed on a comet surface, A’Hearn said.

There is also a large, flat area that curves around the surface of the nucleus. The only flat area previously observed was a plateau on Borrelly.

“We don’t understand the physics of what produces those flat surfaces,” A’Hearn said. Tempel 1’s “orbital history is very similar to Borrelly’s, but the surface looks totally different.”

The impact surprised researchers in both its magnitude and its structure. The sequence of images from the Deep Impact mother ship shows a small flash, a slight delay and then a larger flash, said Peter Schultz of Brown University, a project co-investigator.

That suggests that the 820-pound impactor, which struck the surface of the comet at a speed of 6.3 miles per second, burrowed into a powdery layer in the nucleus before encountering a solid surface of ice or rock below it, Schultz said.

“We are getting an enormous wealth of data even though we can’t yet see the actual impact point,” he said.

Late Monday, researchers from the University of Pennsylvania and University College London said ultraviolet observations from NASA’s Swift satellite showed that the impactor struck a solid structure beneath the powdery surface layer.

Although researchers are analyzing the spectra, “We don’t know exactly what we kicked up yet,” said astronomer Keith Mason of University College London.

Images of the impact taken by the mother ship clearly show the shadow of the debris column spreading across the surface of the nucleus.

Initial imaging with Deep Impact’s infrared spectrometer also showed big changes in the composition of the comet’s corona as the debris from the impact was ejected, Mason said.

There are several unidentified materials in the spectra, strong evidence that the interior of the comet is different from the surface, he said.

Telescopes on the ground reported changes in the abundance of gases observed in the comet’s corona, especially a large increase in water vapor.

Researchers believe that comets represent a kind of time capsule of the materials that were present when the solar system was created 4.6 million years ago.

With the $333-million Deep Impact mission, launched from Florida on Jan. 12, researchers hoped to intercept a comet for the first time and determine what lay under its surface. Analysis of those materials should reveal what kinds of compounds were used in the formation of Earth and other planets.

But the mission was an unusually complex one that researchers compared to hitting one high-speed bullet with another bullet, while observing the impact with a third bullet.

Deep Impact traveled more than 280 million miles in six months before inserting the impactor into the comet’s orbit, where it was overtaken at a speed of 23,000 mph.

Despite the violence of the impact, officials say the collision will have no measurable effect on the orbit of the comet, which is about 83 million miles from Earth near the orbit of Mars. The impact “was like a fly running into a 747,” A’Hearn said.

As images continued to flow to the ground from Deep Impact, A’Hearn said astronomers would be assessing them over “the next weeks, months and years. There’s a wealth of data that will take me to retirement.”

He added that Deep Impact had sent 10% of the data collected during the encounter.

The mother ship survived its passage within 300 miles of the comet unscathed, and all systems were functioning normally Monday, JPL engineers said. Once all of the data has been transmitted to Earth, the craft will effectively be mothballed, with all but the most crucial systems being shut down.

The craft still carries more than 300 pounds of fuel, so it could be reprogrammed to intercept another comet. But that would require a new round of funding, Dantzler said.

Project Manager Rick Grammier said the team had not intended to make a statement by having the impactor reach the comet just before Independence Day. But, he added, “That’s something to be proud of on America’s birthday.”