Deep Impact was a NASA space probe launched from Cape Canaveral Air Force Station on January 12, 2005. It was designed to study the interior composition of the comet Tempel 1 (9P/Tempel), by releasing an impactor into the comet. At 05:52 UTC on July 4, 2005, the Impactor successfully collided with the comet's nucleus.
The impact excavated debris from the interior of the nucleus, forming an impact crater. Photographs taken by the spacecraft showed the comet to be more dusty and less icy than had been expected. The impact generated an unexpectedly large and bright dust cloud, obscuring the view of the impact crater.
Previous space missions to comets, such as Giotto, Deep Space 1, and Stardust, were fly-by missions. These missions were able to photograph and examine only the surfaces of cometary nuclei, and even then from considerable distances.
The Deep Impact mission was the first to eject material from a comet's surface, and the mission garnered considerable publicity from the media, international scientists, and amateur astronomers alike.
Upon the completion of its primary mission, proposals were made to further utilize the spacecraft. Consequently, Deep Impact flew by Earth on December 31, 2007 on its way to an extended mission, designated EPOXI, with a dual purpose to study extrasolar planets and comet Hartley 2 (103P/Hartley). Communication was unexpectedly lost in August 2013 while the craft was heading for another asteroid flyby.
More information: NASA
The Deep Impact mission was planned to help answer fundamental questions about comets, which included what makes up the composition of the comet's nucleus, what depth the crater would reach from the impact, and where the comet originated in its formation.
By observing the composition of the comet, astronomers hoped to determine how comets form based on the differences between the interior and exterior makeup of the comet. Observations of the impact and its aftermath would allow astronomers to attempt to determine the answers to these questions.
The mission's Principal Investigator was Michael A'Hearn, an astronomer at the University of Maryland. He led the science team, which included members from Cornell University, University of Maryland, University of Arizona, Brown University, Belton Space Exploration Initiatives, JPL, University of Hawaii, SAIC, Ball Aerospace, and Max-Planck-Institut für extraterrestrische Physik.
Following its launch from Cape Canaveral Air Force Station pad SLC-17B at 18:47 UTC on January 12, 2005, the Deep Impact spacecraft traveled 429 million km in 174 days to reach comet Tempel 1 at a cruising speed of 28.6 km/s.
More information: Jet Propulsion Laboratory-NASA
Once the spacecraft reached the vicinity of the comet on July 3, 2005, it separated into the Impactor and Flyby sections. The Impactor used its thrusters to move into the path of the comet, impacting 24 hours later at a relative speed of 10.3 km/s.
The Impactor delivered 1.96×1010 joules of kinetic energy -the equivalent of 4.7 tons of TNT. Scientists believed that the energy of the high-velocity collision would be sufficient to excavate a crater up to 100 m wide, larger than the bowl of the Roman Colosseum. The size of the crater was still not known one year after the impact. The 2007 Stardust spacecraft's NExT mission determined the crater's diameter to be 150 meters.
Just minutes after the impact, the Flyby probe passed by the nucleus at a close distance of 500 km, taking pictures of the crater position, the ejecta plume, and the entire cometary nucleus. The entire event was also photographed by Earth-based telescopes and orbital observatories, including Hubble, Chandra, Spitzer, and XMM-Newton.
The impact was also observed by cameras and spectroscopes on board Europe's Rosetta spacecraft, which was about 80 million km from the comet at the time of impact. Rosetta determined the composition of the gas and dust cloud that was kicked up by the impact.
More information: Solar System Exploration-NASA
Mark Rober
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