Giotto: 30 years on

Three decades ago ESA's first deep space probe flew past one of the most well known objects in the Solar System, Halley's Comet

Giotto_approaching_Comet_Halley

As it approached Halley’s Comet, Giotto managed to snap images of the icy nucleus and tail. Credit: ESA/Giotto/HMC – Copyright MPAe/MPS 1986

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30 years ago ESA’s first deep space probe, Giotto, flew past Halley’s Comet.

On 13-14 March 1986, the probe passed a mere 596km from the nucleus, the first time such a flyby had been done

Giotto was launched on 2 July 1985 to take advantage of the close approach of Halley’s Comet during its 75 year orbit.

Eight months later it began to approach the comet, travelling at a speed of 245,000km per hour relative to the icy body.

As it approached, the probe began to take images of the 15km nucleus and used spectrometers to determine its composition.

But as it got closer, Giotto was bombarded by ice and dust particles.

A large one of these, weighing around a gram, struck the probe 7.6 seconds before closest approach and sent it spinning.

The probe’s thrusters managed to stabilise it 32 minutes later, but by then the probe was returning to deep space.

Despite the set back, Giotto returned a great deal of science data and images.

The researchers at ESA were able to determine that the comet was 80 per cent water, 10 per cent carbon monoxide, with the rest being composed of a mix of hydrocarbons.

It also found that the comet was dark and covered with a thick layer of dust.

After completing its flyby of the icy body, Giotto continued on to comet 26P/Grigg-Skjellerup, approaching an even closer 200km in 1992.

Unfortunately the previous encounter with Halley had damaged many of Giotto’s instruments, including its camera and so it could not take images.

Giotto was one of five spacecraft sent by the world’s space agencies that rushed to take advantage of the rare event – a close pass by a large and active comet.

The Soviet Union sent the twin probes Vega-1 and Vega-2 which, after a pit stop to drop a probe on Venus, carried on to the comet in 1986, while Japan sent their first interplanetary missions Sakigake and Suisei.

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Together the probes, often referred to as Halley’s Armada, analysed the comet’s nucleus and tail and would remain the most comprehensive look at a comet until ESA’s next comet mission, Rosetta.