NASA Launches Deep Impact Spacecraft

Context

By the late 1990s, NASA’s Discovery Program had established a track record of selecting compact, lower-cost missions to address targeted questions in solar system science. Earlier comet encounters, including Giotto’s 1986 flyby of Halley and the later Deep Space 1 and Stardust missions, had returned images and spectra only of cometary exteriors, leaving the interior composition and structure largely unknown. Comets were widely viewed as preserved relics from the solar system’s formation, and scientists sought direct samples of subsurface material to test models of how these bodies accreted and how they might have delivered water and organics to the inner planets.

What Happened

On January 12, 2005, at 18:47 UTC, the Deep Impact spacecraft separated from its Delta II 7925 launch vehicle at Cape Canaveral’s Space Launch Complex 17B. The 973-kilogram probe, built by Ball Aerospace in Boulder, Colorado, in partnership with the University of Maryland science team, consisted of a 601-kilogram flyby spacecraft and a 372-kilogram copper-core impactor. The mission, selected under the Discovery Program and managed by NASA’s Jet Propulsion Laboratory, carried high-resolution imaging instruments and an infrared spectrometer intended to observe the results of a planned collision with Comet 9P/Tempel 1.

Aftermath

The spacecraft completed a six-month cruise of more than 400 million kilometers and arrived at Tempel 1 in early July 2005. On July 3 the impactor was released; twenty-four hours later it struck the nucleus at approximately 10.3 km/s, excavating an estimated 150-meter crater and lofting a plume of dust and ice that was imaged by the surviving flyby spacecraft and by ground- and space-based observatories. The flyby section continued to transmit data showing the comet’s unexpectedly powdery, low-density interior and the presence of water ice and organic compounds.

Legacy

Deep Impact became the first spacecraft to deliberately impact a comet nucleus, demonstrating the practicality of kinetic-impact techniques later considered for planetary defense. Its findings refined models of cometary structure and composition and directly informed the extended EPOXI mission, which redirected the spacecraft to Comet Hartley 2 in 2010. The mission’s public visibility also sustained interest in small-body exploration within NASA’s Discovery and New Frontiers programs.