Newswise — It was midnight New Year's Eve, Christmas morning, Thanksgiving and Labor Day all rolled into one. At least it felt that way for University of Maryland astronomer Michael A'Hearn and his Deep Impact colleagues on January 12 when the spacecraft for NASA's Deep Impact mission successfully launched into a blue Florida sky on a six-month journey to encounter a speeding comet.
"We are all elated at the successful launch," said A'Hearn, principal investigator for the Deep Impact mission. "For the last couple of days it has been a challenge not to worry, since in the last stages, the launch is out of our hands. Now that we are in flight and talking to the spacecraft, we will resume all our testing to ensure that we are successful when we get to Comet Tempel 1."
"That was awesome," said a jubilant Lucy McFadden, University of Maryland research scientist and co-investigator for the mission. "We're heading for the heart of Tempel 1," she said as the Deep Impact spacecraft disappeared into the sky.
"It is exciting, humbling and a little frightening to go out into the unknown," she reflected after some minutes. "But we've got a great team here, so it will be all right."
Led by Maryland's A'Hearn, the Deep Impact team is now working toward and looking forward to the mission's biggest "holiday," July 4th , when Deep Impact will be the first mission to smash a hole in a comet and reveal the secrets of its interior.
Comets are balls of ice, gas and dust that orbit the sun. Scientists believe that the permanently frozen cores of comets contain primitive debris from the solar system's formation some 4.5 billion years ago. Comets that hit the Earth in its early history may even have provided the water and organic compounds that were the precursors of life on our planet.
"The information we gain from Deep Impact should significantly improve our understanding of how our solar system formed," says A'Hearn. "It also will increase our knowledge of the density and composition of comets, information that could be vital should a comet ever threaten Earth." A July 4th Collision
Deep Impact consists of two spacecraft -- a flyby spacecraft about the size of a compact car and a large (3 ft. by 3 ft.) trash-can-sized "impactor." At the beginning of July, after a voyage of some 268 million miles, the joined spacecraft will reach their target, Comet Tempel 1. The spacecraft will approach the comet and collect images of it. Then, 24 hours before the July 4th impact, the flyby spacecraft will launch the copper impactor into the path of the onrushing comet.
Like a flying bug overtaken and smashed into the grill of a speeding tractor-trailer truck, the 820-pound impactor will be run down by the comet at a collision speed of some 23,000 miles per hour. There are no explosives aboard the impactor, but the kinetic energy of the impact will be equivalent to almost five tons of TNT.
A'Hearn and his fellow scientists expect the resulting crater to range in size from that of a house to a football stadium, and from two to fourteen stories deep. They expect to see ice and dust ejected from the crater, revealing pristine material beneath. The impact will not significantly affect the orbit of Tempel 1, which poses no threat to earth.
Deep Impact's flyby spacecraft will collect pictures and data of the event and send them back to Earth. There will also be many other "eyes" on the sky that night. NASA's Chandra, Hubble and Spitzer space telescopes will be observing from near-Earth space. Professional and amateur astronomers on Earth also will observe the comet before, during and after the formation of the crater.
The data from all these sources will be analyzed and combined with that from other comet missions to provide a better understanding of both the solar system's formation and the risk of comets some day colliding with Earth, as occurred in the distant past.
Recent Comet Missions
The Deep Impact mission is the eighth in NASA's Discovery Program and the third targeted at a comet. The Stardust mission, launched in February 1999, flew through the coma, or cloud, surrounding the nucleus of Comet Wild 2 in January 2004. It collected samples of cometary and interstellar dust, which will be returned to Earth for study in January 2006. The Comet Nucleus Tour, or CONTOUR, mission was launched in July 2002. Unfortunately, six weeks later, on Aug. 15, contact with the spacecraft was lost.
A European Space Agency mission, Rosetta, was launched in March 2004, on a trip to orbit comet 67P/Churyumov-Gerasimenko. In 2014, it is scheduled to deliver a scientific instrument package via a lander to the comet's surface.
To date, even basic properties such as mass and density have never been measured in a any cometary nucleus. Deep Impact will provide the first data probing below the surface of a cometary nucleus and should allow determination of the density of the surface layers. However, determining the mass and overall density of a comet will have to wait until Rosetta mission arrives at its destination.
The Deep Impact Team
A partnership among the University of Maryland, the Jet Propulsion Laboratory (JPL), and Ball Aerospace & Technologies Corp., is conducting the Deep Impact mission. The university, through Principal Investigator Michael A'Hearn, is responsible for the entire mission and directly manages the scientific effort, education and outreach, and the development of the instruments on the spacecraft. University of Maryland research scientist Lucy McFadden is a co-investigator and director of education and public outreach for the mission.
Other university members of the Deep Impact team include Dennis Wellnitz, faculty research scientist who was technical manager of the instrument contract; Stephanie McLaughlin, faculty research assistant in the department of astronomy and coordinator for Deep Impact's Small Telescope Science Program; Carey M. (Casey) Lisse, formerly a senior research scientist in the astronomy department and now with the John Hopkins Applied Physics Laboratory; Elizabeth Warner, director of the University of Maryland's campus observatory and Deep Impact website co-curator, liaison to the amateur astronomy community for the mission; and Olivier Groussin, Maryland research associate who is an expert on thermal models of the nucleus of Comet Tempel 1.
The full science team includes 11 other co-investigators and approximately three dozen other scientists and students. The Jet Propulsion Laboratory, through Project Manager Rick Grammier, provides overall project management and will carry out the in-flight operations. Ball Aerospace & Technologies Corp built both the spacecraft and the instruments.
The Discovery Program
Deep Impact is a mission in NASA's Discovery Program of moderately priced solar system exploration missions. Discovery missions are proposed by individual scientists and their chosen teams.
Using the results of peer reviews by both scientists and engineers, NASA has typically selected one or two new missions every two years. Deep Impact was selected from a proposal submitted in 1998. The cost for Deep Impact is $267 million, plus the cost of the launch.
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