Deep Impact, Mission

The first mission to look inside a comet

  • Launched 12 January 2005
  • The spacecraft’s impactor smashed into comet Tempel 1 on 4 July 2005
  • Deep Impact will fly-by comet Hartley 2 in December 2010
Deep Impact originally consisted of two spacecraft, one inside the other. It made a rendezvous with comet Tempel 1. Once in position, the smaller impactor craft separated from the larger spacecraft and was put on a collision course with the comet.

The resulting crash was not powerful enough to change the comet’s course. Instead it produced a large crater and scattered material from the comet into space. This allowed the fly-by craft and its on board instruments to successfully investigate beneath the surface of a comet for the first time.

Scientists are using these observations to better understand comets, the formation of our Solar System and also the possible implications of a comet on a collision course with Earth.

In July 2007, NASA gave both Deep Impact and Stardust new assignments and extended their missions. Deep Impact is now part of the EPOXI mission (Extrasolar Planet Observation and Deep Impact Extended Investigation).

Deep Impact is currently observing nearby bright stars and their giant orbiting planets. Direct observations will also allow scientists to find smaller, more Earth-like planets if gravity from these unseen alien worlds, or extrasolar planets, pulls on these transiting giant planets and affects their orbits.

Mission facts

  • Tempel 1, discovered by Ernst Tempel in 1867, orbits the Sun. It passes through the inner Solar System every five and a half years.

  • The washing machine-sized impactor travelled ten times faster than a speeding bullet shortly before it slammed into Tempel 1.

  • During Deep Impact’s fly-by of Earth, on 31 December 2007, the spacecraft observed the Moon, calibrated its instruments and used our planet’s gravity to assist it towards comet Hartley 2.


The fly-by craft used opitical imaging and infrared mapping technologies to analyse both the comet’s interior and the resulting debris from the crash. The instruments discovered water, microscopic dust, hydrocarbons and carbon dioxide ice.

HRI (High Resolution Instrument), MRI (Medium Resolution Instrument) and ITS (Impactor Targeting Sensor) guided the spacecraft towards the comet and took data readings before and after impact.

The impactor was made from 49 per cent copper to minimise the corruption of spectral emission lines used to analyse the comet nucleus or centre.

A camera on the impactor relayed images of the comet nucleus until seconds before the collision.

UK involvement

UK scientists from the University of Leicester, the Mullard Space Science Laboratory (MSSL) and the University of Cardiff were part of an international team that helped observe and study material ejected from the comet on impact.

The team used the Isaac Newton telescope on La Palma, Spain, to monitor the debris. The UK Schmidt telescope in Australia examined the colours of light emitted during the impact and NASA’s Swift satellite also watched the collision. Both Leicester and MSSL led instruments on Swift.

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