NASA’s Deep Impact mission was the space-related highlight of the year 2005 because, for the first time, a probe smashed into a comet to reveal the secrets of its interior. The Deep Impact probe released the small “impactor” (370 kg), which predominantly consists of copper, 24 hours before arriving at the target, Tempel 1.
The Deep Impact mission was a six-year mission funded by NASA in November 1999. The spacecraft was launched in December 2004 with a Delta II Rocket from the Kennedy Space Center. On July 4, 2005, the spacecraft arrived at the comet.
Comets are composed of ice, gas, and dust and are considered time capsules that hold clues about the formation and evolution of the solar system 4.5 billion years ago. Comet Tempel 1 was discovered in 1867 by Ernst Tempel and orbits the Sun every 5.5 years. This makes Tempel 1 a good target to study evolutionary changes in the mantle, or upper crust. Scientists are eager to learn whether comets exhaust their supply of gas and dust into space or seal it into their interiors.
They would also like to learn about the structure of a comet's interior and how it differs from its dark surface. In particular, the core of a comet remains a mystery.
Some scientists call comets “dirty snowballs,” but newer research suggests that the core of a comet consists more of rocks than ice.
The spacecraft used an X-band radio antenna to communicate with Earth while it also listened to the impactor on a different frequency. For most of the mission, the flyby spacecraft communicated through NASA's Deep Space Network.
A lot of ground- and space-based telescopes, including Hubble, XMM-Newton, and Chandra, observed this event.
Other comet missions include the European spacecraft Giotto, the Rosetta mission, and the American space probe Stardust.
Mission Results:
Crater discovery: The mission successfully excavated a crater on the comet's surface, which was later determined to be 490 feet (150 meters) in diameter.
Comet composition: The impact revealed that the comet's surface layer is very porous, and the data showed that the comet was about 75% empty space.
Comet origin: Scientists concluded that Comet Tempel 1 likely originated in the Oort Cloud.
Dust and ice: Photographs taken by the spacecraft showed the comet to be more dusty and less icy than expected.
Comet structure: The mission provided insights into the internal composition and structure of comets.
Additional discoveries: The mission made several other significant discoveries, including determining that hyperactive comets are driven by carbon dioxide.