ESA Science & Technology05-Jul-2005 16:42:30

Background Science

Past Missions to Study Comets

Launch 12 August 1978: International Cometary Explorer


International Cometary Explorer (ICE) achieved the first ever comet encounter. This NASA spacecraft was originally known as ISEE-3 (International Sun-Earth Explorer). Having completed its original mission, it was reactivated and diverted to pass through the tail of Comet Giacobini-Zinner on 11 September 1985. It also observed Comet Halley from a distance of 28 million km in March 1986.

Launch 15 and 20 December 1984: Vega-1 and Vega-2


Vega-1 and Vega-2, two Russian probes, each left a lander on the surface of Venus as they flew past it on the way to investigate and photograph Comet Halley. Both spacecraft imaged the comet's nucleus, while other experiments studied its nearby dust, plasma, gas, energetic particles and magnetic field. Vega-1 made its closest approach to the comet on 6 March 1986 at a distance of 8890 km. Vega-2 flew to within 8030 km of the comet's nucleus on 9 March 1986.

Launch 8 January 1985 and 19 August 1985: Sakigake and Suisei



Sakigake and Suisei were Japan's first deep space missions. Suisei approached to within 151 000 km of Comet Halley on 8 March 1986 to observe its interactions with the solar wind. Sakigake approached to within 7 million km of the comet on 11 March 1986 in order to study radio and plasma waves.

Launch 2 July 1985: Giotto


Comet Halley's nucleus

Giotto obtained the closest pictures ever taken of a comet at that time. This European Space Agency spacecraft flew past the nucleus of Comet Halley at a distance of less than 600 km on 13 March 1986. Images showed a black, potato-shaped object with active regions which were firing jets of gas and dust into space. Giotto then became the first spacecraft to visit two comets when it passed within 200 km of Comet Grigg-Skjellerup on 10 July 1992. It was placed in hibernation on 23 July 1992, and the spacecraft has since been inactive. Giotto returned to the vicinity of the Earth on 1 July 1999. The distance of its closest approach was very uncertain, the estimate being about 220 000 km, just over half the Earth-Moon distance. No communication with the spacecraft took place at this time. Giotto will continue to orbit the Sun for the foreseeable future, completing six revolutions roughly every seven years.

Launch 25 October 1998: Deep Space 1

Deep Space 1, NASA/JPL/CalTech

Deep Space 1 (DS1) was the first spacecraft in NASA's New Millennium programme. Its primary mission was to test 12 new advanced technologies, particularly ion propulsion. Most of these technologies were validated during the first few months of flight. It then approached to within 26 km of asteroid 9969 Braille on 28 July 1999. The few pictures returned showed that Braille measures about 2.2 km across by 1 km.

Despite the loss of its star tracker navigation system, the mission was extended and Deep Space 1 completed a successful flyby of Comet Borrelly on 22 September 2001, passing within 2200 km of the comet. Analysis of the 30 or so black and white pictures of the bowling-pin-shaped nucleus showed that it was about 8 km long. Other instruments examined the gas and dust in the surrounding coma and studied the interaction of the comet with the solar wind. DS1 found that the nucleus was not in the centre of the coma, as expected. The coma's 'lopsided' shape was due to a huge jet of material that was shooting into space from one side of the nucleus.

Deep Space 1's mission came to an end on 18 December 2001 when its ion engine was turned off.

Launch 3 July 2002: Comet Nucleus Tour (CONTOUR)

Comet Nucleus Tour.
(Credit: NASA/JHUAPL/Cornell.)

Comet Nucleus Tour (CONTOUR) was a NASA Discovery mission to improve our understanding of comet nuclei. Encounters were planned with Comets Encke (12 November 2003) and Schwassmann-Wachmann 3 (19 June 2006). CONTOUR could also have added an encounter with a 'new' comet from the outer Solar System if one had been discovered in time for the spacecraft to fly past it.

Following the firing of the rockets, contact with the spacecraft was lost. The search for CONTOUR was abandoned in December 2002.

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