This was fortunately not the case for the probes that approached the comet. The Giotto and Vega 2 probes provided the first images of a comet nucleus. The Vega’s images were of poor quality, but they showed that this nucleus was far from spherical. The first image of Giotto was saturated, because the very bright dust emitted by the comet nucleus was centered by the camera.
Fortunately, after the initial fear, one managed to get a good image. Surprise: the nucleus was very dark, almost black, and that was why it had been so hard to see. It was probably covered by a dust layer, under which the ice was buried. It sublimated in some areas under the effect of heating by the Sun, forming jets whose extensions were the famous plumes described by Arago.
The scientific observation devices installed in the different probes generally worked well. A particularly interesting result was obtained by the infrared spectrometer IKS built by France, which detected for the first time several parent molecules directly emitted by the nucleus, before they were destroyed or ionized by the solar ultraviolet radiation. One could see the signature of water vapor (already observed with great difficulty from a stratospheric plane), carbon monoxide, carbon dioxide and formaldehyde H2CO. The encounter with Halley’s comet decidedly marked a new era in our understanding of comets.