Deep Impact, a space mission to study the structure of a comet's deep interior, was one of two missions selected by NASA on 7 July for its Discovery program. The other mission, called Messenger, is designed to do an orbital exploration of the planet Mercury. Deep Impact, whose name was chosen well before the motion picture of the same name was announced, will be led by PI Michael A'Hearn (Maryland). The Deputy PI will be Michael J.S. Belton (NOAO).
The spacecraft will be launched in January 2004 and follow a trajectory that will allow it to deliver a 500 kg impactor to comet P/Tempel 1 at hypersonic speed on 4 July 2005. The impact will excavate a crater in the cometary surface more than 100-m in diameter and more than 20-m deep. This is expected to punch through the first few meters of highly evolved surface materials to the more primitive material expected (on the basis of simple models) at depth. Instruments on the delivery vehicle will make time-resolved spectroscopic and imaging measurements on the progress of the formation of the crater, which will take several minutes, on the nature of the ejecta, and on the nature of the cometary materials that are exposed. Resolution of questions associated with the primitive composition and internal structure of these objects, which may have interiors essentially unchanged since the origin of the solar system, is expected.
The original concept studies performed for Deep Impact were done at NOAO in cooperation with Ball Aerospace and the Jet Propulsion Laboratory in which a "dumb" impactor was targeted to the suspected dead comet Phatheon. The current winning concept, which is now selected for flight, built on this foundation and, under the leadership of A'Hearn at the University of Maryland, now has an active periodic comet as the target and includes many novel and ingenious technical innovations. The most significant of these is a "smart" impactor.
The impact event will be visible from the Earth and a scientific program of worldwide groundbased observations will be coordinated by mission science team member Karen Meech (Hawaii).
Lucy McFadden (Maryland), the Director for Public Education and Outreach for the mission, said that because the impact will be spectacular and visible through small telescopes, the mission should be of great interest to the public and provide a tremendous opportunity for students and others to learn more about comets, the formation of the solar system, and the role of comets in the history of the Earth.
The total cost of Deep Impact to NASA is $240 million. NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California will manage the technical implementation. The project manager at JPL is James E. Graf. Ball Aerospace and Technology Corporation in Boulder, Colorado is responsible for all flight hardware.
Further information about the mission is available at: http://www.ball.com/aerospace/deepimpact.html .
Sidney C. Wolff