NASA Spacecraft’s Impact Wide and Deep

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

Based on images taken by Deep Impact’s Flyby mothership, which tracked the Impactor’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,” Deep Impact co-investigator Peter Schultz said during a July 4 press conference 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 371-kilogram Impactor probe collided with Tempel 1 05:52 GMT July 4.

“I just can’t believe it. It’s absolutely incredible,” said Alice Phinney, lead mechanical design engineer for the Impactor at Ball Aerospace in Boulder, Colo., which designed and built the Flyby spacecraft and the Impactor. She was one of over 600 company colleagues and friends that gathered at Boulder’s Fiske Planetarium.

Phinney said she worked on the Impactor that smashed into the comet for some two years. One of her key jobs was maximizing the use of copper in the Impactor design. The task was not as straightforward as it would seem. “There were a lot of assumptions. Scientists were all over the map,” Phinney said regarding the overall composition of Comet Tempel 1.

“We saw some pretty spectacular things happen at impact,” said Jessica Sunshine, a co-investigator on the Deep Impact team’s spectrometer instrument. “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, College Park, told reporters that the next task is pinning down the size of the crater created after the Impactor crashed into the comet.

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

Mission scientists are eager to collect all the data from the Flyby spacecraft, 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.

“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 said.

Deep Impact researchers and engineers had set up a betting pool about 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 you’re slamming objects together like this.”

The comet’s average range of temperature 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 [should] 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.”

The best is yet to come, Sunshine said July 4. 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.

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

McFadden said lab experiments were carried out by researchers, as were computer simulations – all to help formulate the team’s scientific hypotheses about what was likely to 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 what…it 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.

SPACE.com Senior Space Writer Leonard David contributed to this story from Boulder, Colo.