Afterglow: NASA Lauds Deep Impact's Comet Crash
This image shows the initial ejecta that resulted when NASA's Deep Impact probe collided with comet Tempel 1 at 10:52 p.m. Pacific time, July 3 (1:52 a.m. Eastern time, July 4). It was taken by the spacecraft's medium-resolution camera 16 seconds after impact.
Credit: NASA/JPL-Caltech/UMD.

PASADENA -- Deep Impact scientists and engineers are lauding their mission's successful collision with Comet Tempel 1 and are already drawing some conclusions about the icy wanderer.

Based on images taken by Deep Impact's Flyby mothership, which tracked the mission's collision with Tempel 1, astronomers believe the comet's surface was covered in a soft material.

"This was probably a soft surface, a dusty surface," explained said Deep Impact co-investigator Peter Schultz during a press conference today at NASA's Jet Propulsion Laboratory (JPL). "I've made a living playing in a sandbox, and now I can say I've played with a comet."

The press conference - the second mission update today - was preceded by the song Rock Around the Clock by Bill Hailey and the Comets. The surviving members of the Comets will perform tomorrow for the Deep Impact team as part of a mission's success celebration.

Deep Impact's Flyby spacecraft captures Imapactor's flash during the Tempel 1 collision in this movie assembled from images taken by its high-resolution camera. Credit: NASA/JPL-Caltech/UMD. Click to view.

Researchers were able to present additional images of the 820-pound (371-kilogram) Impactor probe's collision with Tempel 1, which occurred at 1:52 a.m. EDT (0552 GMT) on July 4.

"We saw some pretty spectacular things happen at impact," Jessica Sunshine, a co-investigator on the Deep Impact team's spectrometer instrument, told "It got really hot, then we saw it cool down and we saw significant amounts of materials come out, we're still trying to understand exactly what."

Michael A'Hearn, Deep Impact's principal investigator at the University of Maryland, told reporters that the next task is pinning down Impactor's crater.

"It's clear that the ejecta was still coming out, at least after the [impact] event," A'Hearn said. "If there're a lot of volatiles there, the outgassing would continue."

Mission scientists are eager to collect all the data from Flyby, but do not currently have plans for an extended mission.

"Once we get all the data down and finish the look back, we'll consider a mothballing procedure," said Rick Grammier, Deep Impact project manager at JPL.

A hot collision

The increase in heat happened very quickly during Impactor's collision, which researchers expected based on test models, Sunshine said.

This movie, compiled from Impactor's images, shows the probe's apporach to Comet Tempel 1. Credit: NASA/JPL-Caltech/UMD. Click to enlarge.

"What we didn't know, and we still don't know was how long did the increase last? What materials were ejected? How quickly does it cool down? We're still trying to plow through that," she added.

Deep Impact researchers and engineers had set up a pool over the possible effects of Impactor's collision. While it is still unknown how large the resulting crater is, some researchers have ventured to make their own estimates.

"I don't think it's house-sized, I think it's bigger than that," Schultz said. "I'm sure the [impact temperature] is going to be in the thousands of degrees Kelvin, you get that when your slamming objects together like this."

The average range of temperature of the comet is between 240 and 300 Kelvins, which is consistent with a body as far from the Sun as Tempel 1, researchers said.

"The thermal map we showed today was fairly far out," Sunshine said. "We have a map of before and after with much greater detail. We have the nucleus at seven meters, its closest approach, so we will really be able to tie that information with some of the visible morphology and try to understand how the comet retains heat, which is an important issue for how it outgases."

Meanwhile, still only about 10 percent of the data collected from impact has been transmitted.

"It's frustrating for us," Sunshine said with a smile. "The spectrometer is a data hog. It takes the longest to come down. I will take about four days before it all comes down."

Even so, the best is yet to come, Sunshine said. The time series showing the Impactor heading towards the comet is only the tip of the iceberg. "The movie is going to get better."

Just like the simulations

The Deep Impact science team is elated given the success of the Impactor.

This image looking back at Tempel 1 was taken by the high-resolution camera aboard Deep Impact's flyby spacecraft. Credit: NASA/JPL-Caltech/UMD. Click to enlarge.

"We are all beside ourselves," said Lucy McFadden, Deep Impact science team co-investigator at the University of Maryland, in an interview. "We did everything we were supposed to do when we plan an experiment."

McFadden told that lab experiments were carried out by researchers, as were computer simulations - all to make the team's scientific hypotheses about what might be seen when the Impactor collided with Tempel 1.

"We planned our experiment and conducted it. All along we tried not to be too sure of ourselves. So with humility, we thought that something entirely different would actually happen," McFadden said. "But guess happened almost as one of our models predicted.

The model that literally hit the mark, McFadden said, was the one where the comet is very porous and gravitationally bound. The Impactor produced a dramatic ejecta curtain that was bound to the comet, she added.

"We are ecstatic, and very tired. I think I'll have a smile on my face for many months," McFadden said.

People shouldn't be worried about the impact, Sunshine said.

"This is nothing new to the comet," she said. "Every body in the solar system has had impacts on it, including ours. Comets are no different. What we're trying to understand is how does it react to this controlled experiment."

The team was fortunate that Tempel 1 experienced naturally occurring outbursts in the weeks prior to the collision.

"We were lucky enough to capture some natural outbursts and now we can try to compare those with what we saw at impact in terms of material that came out and how deep we think this crater went," Sunshine said. Senior Space Writer Leonard David contributed to this story from Boulder, Colorado.

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