Halley's Comet (1P/Halley)
Halley's Comet goes around the Sun once every 76 years – roughly a human lifetime. Upon its return to the inner solar system in 1986, it was met by a small flotilla of spacecraft, including ESA's Giotto, Japans Sakigake and Suisei, and Russias twin Vega probes.
Giotto sent back images of Halley's potato-shaped nucleus (see photo right), measuring 16 × 8 km (10 × 5 miles). The nucleus is dark, reflecting only 4% of the sunlight falling on it, and rotates once every 3.7 days. On the sunward side, temperatures were observed to reach 77°C (350 K) which, in the zero pressure of space, is enough to turn ice into vapor. Measurements by Giotto's mass spectrometer indicated a composition for Halley of 45% water ice, 28% stony minerals, and 27% organic material.
Related category COMETS
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