Below are several first-report articles on the comet impact. However, to really see what is happening, I strongly recommend the images and movies on the mission website http://deepimpact.jpl.nasa.gov -- especially the approach movie showing the comet from the probe, and the impact movie made with the cameras on the mother craft. David Morrison ========================== JPL/NASA NEWS RELEASE: 2005-110 July 4, 2005 NASA'S DEEP IMPACT GENERATES ITS OWN SPECTACULAR PHOTO FLASH The hyper-speed demise of NASA's Deep Impact probe generated an immense flash of light, which provided an excellent light source for the two cameras on the Deep Impact mothership. Deep Impact scientists theorize the 820-pound impactor vaporized deep below the comet's surface when the two collided at 1:52 am July 4, at a speed of about 10 kilometers per second. "You can not help but get a big flash when objects meet at 23,000 miles per hour," said Deep Impact co-investigator Dr. Pete Schultz of Brown University, Providence, R.I. "The heat produced by impact was at least several thousand degrees Kelvin and at that extreme temperature just about any material begins to glow. Essentially, we generated our own incandescent photo flash for less than a second." The flash created by the impact was just one of the visual surprises that confronted the Deep Impact team. Preliminary assessment of the images and data downlinked from the flyby spacecraft have provided an amazing glimpse into the life of a comet. "They say a picture can speak a thousand words," said Deep Impact Project Manager Rick Grammier of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "But when you take a look at some of the ones we captured in the early morning hours of July 4, 2005 I think you can write a whole encyclopedia." At a news conference held later on July 4, Deep Impact team members displayed a movie depicting the final moments of the impactor's life. The final image from the impactor was transmitted from the short-lived probe three seconds before it met its fiery end. "The final image was taken from a distance of about 30 kilometers from the comet's surface," said Deep Impact Principal Investigator Dr. Michael A'Hearn of the University of Maryland, College Park. "From that close distance we can resolve features on the surface that are less than 4 meters (about 13 feet) across. When I signed on for this mission I wanted to get a close-up look at a comet, but this is ridiculousý in a great way." The Deep Impact scientists are not the only ones taking a close look at their collected data. The mission's flight controller team is analyzing the impactor's final hours of flight. When the real-time telemetry came in after the impactor's first rocket firing, it showed the impactor moving away from the comet's path. "It is fair to say we were monitoring the flight path of the impactor pretty closely," said Deep Impact navigator Shyam Bhaskaran of JPL. "Due to the flight software program, this initial maneuver moved us seven kilometers off course. This was not unexpected but at the same time not something we hoped to see. But then the second and third maneuvers put us right where we wanted to be." The Deep Impact mission was implemented to provide a glimpse beneath the surface of a comet, where material from the solar system's formation remains relatively unchanged. Mission scientists hoped the project would answer basic questions about how the solar system formed, by providing an in-depth picture of the nature and composition of the frozen celestial travelers known as comets. The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. =============================================== AFTERGLOW: NASA LAUDS DEEP IMPACT'S COMET CRASH By Tariq Malik & Anthony Duignan-Cabrera Space.com -- posted: 4 July 2005 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. Researchers were able to present additional images of the 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 SPACE.com. "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. 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 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. ýIt's frustrating for us,ý 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." The Deep Impact science team is elated given the success of the Impactor. "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 SPACE.com 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 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. "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. "Everybody 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. SPACE.com Senior Space Writer Leonard David contributed to this story from Boulder, Colorado. ============================================== San Jose Mercury News Posted on Tue, Jul. 05, 2005 JUBILANT SCIENTISTS COLLECT EXPLOSION OF DATA AFTER NASA PROBE'S 268-MILLION-MILE BULLS-EYE By Glennda Chui PASADENA - It seemed the whole world was watching Sunday night as NASA's Deep Impact probe took its historic plunge into a comet, releasing explosive plumes of gas and dust that astonished even the experts with their brilliance. At two briefings starting at 1 a.m. Monday at NASA's Jet Propulsion Laboratory, scientists and engineers -- exultant, exhausted, barely believing their luck -- said the high-risk mission, the first ever to hit a comet, could not have gone better. "We were right on target," said Rick Grammier, the mission's project manager. "We made it happen, and it happened like clockwork, and I think that's something to be proud of on America's birthday." While the impact itself was a stunning achievement -- after a journey of 173 days and 268 million miles, the probe hit just yards from its intended target -- a lot of hard work lies ahead, scientists said. They still don't know the shape of the comet's nucleus, an elongated, tar black, craggy hunk of ice, dust and rock about nine miles long and three miles wide. Until Sunday it was only a pinpoint of light. In the first close-ups it looks like a pear, or maybe a muffin; but the pictures show it from one end, and its true three-dimensional shape will become apparent only as the rest rotates into view. Scientists still have to figure out how tall and hot the plume was, exactly what was in it and what the crater looks like. Some of the biggest scientific payoffs for the $333 million mission could come in the weeks ahead, said Karen Meech, an astronomer from the University of Hawaii-Manoa who is coordinating worldwide observations. Virtually every major observatory in the world, as well as many smaller ones and at least nine spacecraft, has its eyes on the evolving show. "A lot of our folks are actually predicting new plumes," as heat generated by the impact spreads into the comet's interior, she said. "It may take hours to days to reach absolutely fresh ices," she said, vaporizing them so they leak out and give scientists their first glimpse of primordial material frozen inside the comet since the birth of the solar system. On Monday, Meech was plowing through hundreds of e-mails from researchers around the world, who had agreed to share their data as fast as they could gather it. She was collecting information from China and India, where scientists were just finishing their night's observations, and passing it to researchers on Chile's Cerro Paranal, where the sun was about to set. Ordinary people also followed the action -- surfing the Web, setting up telescopes in parks and parking lots and joining public viewing events such as the one at Chabot Space & Science Center in Oakland, where 500 people bought tickets to watch NASA coverage and check out the view through a 36-inch telescope named Nellie. Grammier said the National Aeronautics and Space Administration's Web site got a billion hits in the 24 hours surrounding the impact at 10:52 p.m. PDT Sunday. He said that's two and half times as many hits as the Mars rover missions drew on their busiest day. "I was trying to think of how to describe this, and I'm just plain speechless," said Andrew Dantzler, director of NASA's solar system division. "I don't think anybody expected it to go so beautifully well." Nowhere was the impact visible to the naked eye -- not even from 13,800-foot Mauna Kea, where Meech took a few minutes off to stare at the sky. Despite the best viewing conditions in the world, she said, "We did not see anything." But groundlings did get a ringside seat through NASA television, which broadcast stunning pictures snapped by the probe as it plunged to its death -- the last one taken just three seconds before impact. Minutes later, the flyby spacecraft sent back the first look at the impact from about 5,000 miles away. Later these images will be "gussied up," as one astronomer put it -- processed to make them sharper, extract scientific information and maybe subtract some of the dust in the plume to reveal the crater beneath. But what the first pictures lacked in polish they made up in immediacy. The public saw critical parts of this historic event at the same moment the scientists and the engineers did. No one involved in the mission wore a bigger grin than Peter Schultz, an astronomer at Brown University who has spent 30 years studying craters at NASA's Ames Research Center in Mountain View. Set up in the Apollo days to simulate craters on the moon, the Ames Vertical Gun Range fires BB-sized projectiles at 10 times the speed of a bullet into mixtures that mimic the surface of a heavenly body -- whether a planet, moon or the solid part of a comet, known as its nucleus. To approximate Comet Tempel 1, Schultz used odd mixtures of ice, dry ice, garden perlite, window cleaner and even Worcestershire sauce, which contains dark, carbon-rich compounds like those found in the crusty dark skin of a mature comet. Based on the Ames experiments, he said, it looks like the first bright, strobe-light flash from the impact -- so brief that the eye couldn't really take it in -- came from the impactor hitting a soft, dusty surface at least several yards thick. In less than a tenth of a second, he said, it had penetrated deep, pushing and compressing the material ahead of it until it could go no further. It was like hitting a brick wall; the crater exploded, creating a second, even brighter flash. An incandescent plume of gas and dust, heated to thousands of degrees and glowing like a bulb, flared like a Roman candle into space, throwing a dark shadow onto the surface of the nucleus. Then a cone of dust and debris rose from the crater and spread like a fan, brilliantly lit by the sun. Scientists with the Hubble Space Telescope estimate that it traveled 1,100 mph, twice the speed of a commercial jet. Over the next 15 minutes, observers on the ground and in space -- from the Hubble to Lick Observatory on Mount Hamilton - watched the faint comet, 83 million miles away, grow four to five times brighter. The engineering team did have some anxious moments as the impactor sped toward its target. Released from the flyby spacecraft on Saturday, it had just three chances to correct its course and steer toward the comet in the 90 minutes before it crashed. Just before the release, it looked like the impactor might miss, aiming just off the left shoulder of the comet, said Shyam Bhaskaran of JPL, the mission navigator. The first course correction put it even farther away. "This wasn't entirely unexpected," Bhaskaran said, "yet it does make you nervous." But the second and third corrections not only set it straight, but aimed at it a region that would give the flyby spacecraft the best view of the crater and plume. Schultz said his work on the comet is far from over. Based on what they saw Sunday night, he said, he and his students will fine-tune their experiments at Ames and try to create a twin of the impact crater in their lab. "We've been living on adrenaline, trying to interpret this," Schultz said Monday morning, after getting to bed at 5 a.m. and sleeping through 90 minutes of a ringing alarm clock and two phone calls. "It just blows you away." =============================================== New York Times, July 5, 2005 SPACECRAFT HITS PASSING COMET, JUST AS PLANNED By WARREN E. LEARY WASHINGTON, July 4 - NASA's 83-million-mile shot at a comet was a bull's-eye. Its Deep Impact spacecraft slammed into its target with such force early Monday that the resulting blast of icy debris stunned scientists with its size and brightness. If you could hear sounds in space, it would have been a big bang. With the second stage of the two-part spacecraft, known as the flyby stage, watching from a safe distance, an 820-pound copper-core "impactor" craft smashed into the nucleus of comet Tempel 1 at 23,000 miles an hour, sending a huge spray of debris into space. "The impact was spectacular," said Dr. Michael A'Hearn of the University of Maryland, the project's principal scientist. "It was much brighter than I expected." Culminating a six-month journey to a point 83 million miles from Earth, the impactor guided itself to a point near the bottom of the elongated comet where they collided at 1:52 a.m. Eastern time with a force equal to four and a half tons of dynamite. Scientists had only one chance for a collision with their fast-moving target. With radio communications taking more than seven minutes each way, the spacecraft was on its own to complete the mission. Just 24 hours before intercepting Tempel 1, springs separated the larger flyby craft from the impactor, leaving the projectile in the path of the comet as the mother craft veered away. The impactor turned on its automatic navigation system two hours before impact and made three course maneuvers to pick a well-lit spot on the sunny side of the comet to hit. It was right on target. "We've touched a comet, and we've touched it hard," Dr. Peter H. Schultz of Brown University, another main investigator, said at one of two news conferences at NASA's Jet Propulsion Laboratory in Pasadena, Calif., which controlled the flight. The purpose of the $333 million mission was to make the most detailed study of a comet to date, striking the mountain-sized hunk of ice and rock, and creating a crater from which would spew some of the primal material that makes up its core. The material, to be analyzed using instruments on the flyby craft, may hold clues to the formation of the solar system 4.5 billion years ago. Depending upon the comet's composition, scientists speculated that the impact could leave a crater as large as a stadium or as small as a house. Dr. A'Hearn said the blast was so bright that initial images did not reveal the crater's size or depth. Those are to be revealed in later images recorded by the flyby spacecraft when they are received, he said. In some pictures, Dr. A'Hearn said, scientists see a feature or shadow where the crater would be, but it will take a week or more of image processing to be sure. Dr. Schultz said he did not want to guess the size of the crater. But he added: "I don't think it's house-sized. I think it's bigger than that." Even as it picked a target point on the Sun side of the comet and navigated toward it, the battery-powered impactor took increasingly detailed pictures with its telescopic camera, shooting its last image just 3.7 seconds before the collision. Late images from the impactor, the best ever taken of a comet, showed a Moon-like surface with flat plains, circular craters and a long, irregular ridge. Some of the last pictures appeared to show the impactor coming in between two mile wide craters on the deeply textured surface. Scientists are interested in comets because they are believed to be remnants of the materials that formed the solar system. Astronomers believe that comet interiors have undergone little change since then and contain the pristine ice, gases, dust and other materials from which the rest of the solar system formed. A secondary reason to probe comets is that along with rocky asteroids, they pose the threat of cataclysmic damage if they ever strike Earth. Potential planetary defense, Dr. A'Hearn said, requires knowing more about these objects and their composition in hopes of deflecting or destroying dangerous ones. Sequential pictures of the impact with Tempel 1 seem to indicate a two-stage explosion caused by the energy of the penetrating spacecraft, Dr. Schultz said. First, a small flash ejecting an umbrella-shaped cloud of debris was shown, then a brief delay was followed by a large flash shooting out a tall vertical column of dust and other material. The impact was also observed by scores of telescopes at ground observatories, as well as NASA's Hubble, Spitzer and Chandra observatories in Earth orbit and other spacecraft. Pictures from the Hubble Space Telescope showed Tempel 1 appearing four times as bright 15 minutes after the collision, and the European Space Agency's XXM-Newton observatory detected evidence of water. Tempel 1, discovered in 1867, is a dark-colored comet that moves about the Sun in an elliptic orbit between Mars and Jupiter every five and a half years. Latest observations indicate it is an elongated object about nine miles long and 3.7 miles across, about half the size of Manhattan. Despite the force of the collision, the comet shrugged it off and continued on its way, undisturbed. Rick Grammier, the mission's project manager at the Jet Propulsion Laboratory, said the encounter came off without a hitch. The flyby craft, equipped with high- and medium-resolution telescopic cameras, monitored the impact from 5,300 miles away. It is also equipped with an infrared spectrometer, which analyzes light frequencies from the ejected material to identify it. The craft emerged undamaged after passing within 310 miles of the comet while ducking behind a set of shields to protect it from dust and other particles streaming from the comet. "We have a healthy flyby spacecraft," Mr. Grammier said. After its close approach, the flyby craft took more pictures of the receding comet. One image, taken from 16,800 miles behind, showed the black end of the comet silhouetted by the glow of dust being ejected thousands of miles into space by the impact. After transmitting all its collected data, the craft will be powered down and "mothballed" in space, with the possibility of activation for another mission. "It is particularly gratifying," Mr. Grammier said, to have such success on Independence Day. "I actually hope it's made America proud," he said. |
