This image of the nucleus of Halley's comet comes from the Giotto spacecraft.
Click on image for full size
Measurements from Halley's comet
Among the things we learned from a suite of spacecraft which visited Halley's comet in 1986 are:
- what a comet nucleus looks like up close (no one had ever seen the nucleus before.)
- that the nucleus had craters and other surface features
- that evaporation occured only from specific jets, or cracks in the surface
- that gases of the coma include H+, C+, OH+, CO+, CN+, N2+, H2O+, CO+, and H3O+, among others. (These measurements help scientists determine more accurately what the nucleus is made of, as well as verifing what ground-based measurements of molecular spectra had suggested was present.)
- how big the coma is, compared to the actual nucleus (100,000 miles vs. 15 miles)
- that instead of being bright like a surface made of ice, the nucleus was "dark", which suggests there may be a significant amount of organic material such as formaldehyde (an organic molecule) on the surface.
- how the magnetic field of the Sun responded to the presence of the comet coma
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