Launch Date: January 12, 2005
The Deep Impact mission was selected as a Discovery mission in 1999. The spacecraft was launched aboard a Delta II rocket on January 12, 2005 and left Earth’s orbit toward Comet Tempel 1. The spacecraft consists of two main sections, the 370 kg copper-core "smart impactor" which impacted the comet, and the "flyby" section, which imaged the comet from a safe distance during the encounter. After imaging the comet, in early July 2005 the larger “flyby” spacecraft pointed high-precision tracking telescopes at Tempel 1 and released the “impactor” spacecraft into the comet’s path for a planned collision to the icy body’s sunlit side.
The impactor was a battery-powered spacecraft that operated independently of the flyby spacecraft for just one day. It was called a “smart” impactor because, after its release, it took over its own navigation and maneuvered into the path of the comet. A camera on the impactor captured and relayed images of the comet’s nucleus until just seconds before collision. The impact was not forceful enough to make an appreciable change in the comet’s orbital path around the Sun.
After release of the impactor, the flyby spacecraft maneuvered to a new path that, at closest approach, passed just 500 km (300 miles) from the comet while taking pictures of the crater position, the ejecta plume, and the entire cometary nucleus. While the flyby spacecraft and impactor did their jobs, professional and amateur astronomers at both large and small telescopes on Earth and in orbit observed the impact and its aftermath. The impact was also observed by Europe's Rosetta spacecraft, which was about 80 million km from the comet at the time of impact.
Scientists were surprised to find that the material excavated by the impact contained more dust and less ice than expected. Spectroscopy of the impact revealed evidence of clays, carbonates, sodium, and crystalline silicates, in addition to a surprisingly high number of organic molecules. The comet nucleus was found to be extremely porous with up to 80% empty space.
The science team estimates the impact blasted a crater about 100 meters wide and up to 30 meters deep, unfortunately, the impact ejecta obscured the view so that the spacecraft was unable to image the final crater. Fortunately, the Stardust spacecraft has been approved to tackle a new mission – the Stardust-NExT (New Exploration of Tempel-1) mission will fly by Tempel-1 in 2011 and observe the new crater.
Like the Stardust spacecraft, the Deep Impact spacecraft has also been repurposed. The Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) is a follow-on mission to Deep Impact, combining two scientific studies; “Deep Impact Extended Investigation (DIXI)” and “Extrasolar Planet Observation and Characterization (EPOCh)”.