ESA Science & Technology05-Jul-2005 16:51:12

Asteroid Encounters


For a long time, the only information obtained on asteroids was through Earth-based observations and photographs. In recent years, some of the larger asteroids have been imaged by the Hubble Space Telescope and radar observations have been made of several asteroids as they pass close to the Earth.

A major breakthrough came in 1983 with the Netherlands - UK - U.S. InfraRed Astronomy Satellite (IRAS), which observed more than 1800 asteroids. Among its discoveries was an unusual asteroid, 3200 Phaethon, which seems to be an extinct comet.

However, most of our knowledge about asteroids comes from close-up observations by spacecraft. These are the missions that have already taken place or are currently planned.

Galileo: On its way to Jupiter, Galileo flew past main belt asteroid 951 Gaspra on 29 October 1991 and obtained the first high resolution images of an asteroid. On 28 August 1993, the spacecraft had a close encounter with main belt asteroid 243 Ida. (NASA)

NEAR Shoemaker (Near Earth Asteroid Rendezvous): A Discovery mission. NEAR made a fast flyby of main belt asteroid 253 Mathilde on 27 June 1997. It then became the first spacecraft to visit a near-Earth asteroid, 433 Eros on 23 December 1998. Orbital insertion failed, but NEAR was able to obtain over 1000 distant images of Eros. During a second attempt, NEAR successfully entered orbit around Eros on 14 February 2000 and began to map its surface at high resolution. On 12 February 2001 it became the first spacecraft to land on an asteroid. (NASA)

Deep Space 1: A New Millennium mission to try out innovative technology, particularly an ion drive and an autonomous navigation system. Completed a flyby of asteroid 9969 Braille, on 28 July 1999, but images were limited to a few distant views when the spacecraft cameras failed to point towards the dark target. (NASA)

Cassini: On its way to Saturn, Cassini crossed the Asteroid Belt and took pictures of asteroid 2685 Masursky on 23 January 2000. The images revealed that the side of Masursky imaged by Cassini is roughly 15 to 20 km across. (NASA/ESA)

Hayabusa (Muses-C): Launched on 9 May 2003. The first Asteroid Sample Return mission. The spacecraft will make a landing on near-Earth asteroid 25143 Itokawa, deploy a tiny microrover and return a soil sample to Earth. (ISAS-JAXA)

Rosetta: Launched on 2 March 2004, it is hoped that Rosetta will encounter one or two main belt asteroids on its way to comet Churyumov-Gerasimenko. (ESA)

Dawn: A NASA mission to rendezvous with and orbit the large main belt asteroids 4 Vesta and 1 Ceres. Scheduled for launch in mid-2006, Dawn will reach Vesta in July 2010. After about one year orbiting the asteroid it will depart for Ceres, arriving in August 2014.

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